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From hus...@apache.org
Subject svn commit: r370938 [37/50] - in /struts: action/trunk/ action/trunk/conf/java/ action/trunk/src/java/org/apache/struts/ action/trunk/src/java/org/apache/struts/action/ action/trunk/src/java/org/apache/struts/chain/ action/trunk/src/java/org/apache/str...
Date Sat, 21 Jan 2006 00:21:00 GMT
Modified: struts/action/trunk/xdocs/userGuide/preface.xml
URL: http://svn.apache.org/viewcvs/struts/action/trunk/xdocs/userGuide/preface.xml?rev=370938&r1=370937&r2=370938&view=diff
==============================================================================
--- struts/action/trunk/xdocs/userGuide/preface.xml (original)
+++ struts/action/trunk/xdocs/userGuide/preface.xml Fri Jan 20 16:19:02 2006
@@ -18,948 +18,1546 @@
 -->
 <document>
 
-  <properties>
-    <title>Preface: Key Technologies</title>
-  </properties>
-
-  <body>
-
-  <section name="0. Preface: Key Technologies">
-
-  <a name="suspects"/>
-  <subsection name="0.1 The Usual Suspects">
-
-    <p>
-      This User Guide is written for active web developers and assumes a working
-      knowledge about how Java web applications are built. Before getting started, you should
-      understand the basics of several key technologies:
-    </p>
-
-    <ul>
-      <li><a href="#http">HTTP, HTML, and User Agents</a></li>
-      <li><a href="#cycle">The HTTP Request/Response Cycle</a></li>
-      <li><a href="#java">The Java Language and Application Frameworks</a></li>
-      <li><a href="#javabeans">JavaBeans</a></li>
-      <li><a href="#resources">Properties Files and  ResourceBundles</a></li>
-      <li><a href="#servlets">Java Servlets</a></li>
-      <li><a href="#jsp">JavaServer Pages and JSP Tag Libraries</a></li>
-      <li><a href="#xml">Extensible Markup Language</a></li>
-      <li><a href="#jaas">JAAS</a></li>
-      <li><a href="#layers">Other Layers</a></li>
-    </ul>
-
-    <p>
-    This chapter briefly defines each of these technologies but does not describe them in detail.
-    For your convenience, links to further information are provided if you would like to learn more about a technology.
-    </p>
-
-    <p id="JavaWebServicesTutorial">If you are familiar with Java, but not these technologies,
-    the best overall starting point is
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/index.html"><strong>The Java Web Services Tutorial</strong></a>.
-    This document is also available for download in
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JavaWSTutorial.pdf">PDF</a> format.
-    </p>
-
-    <p>If you've created web applications for other platforms, you may be able to follow along
-    and visit the other references as needed. The core technologies used by the framework are
-    also used by most other Java web development products, so the background information will be
-    useful in any Java project.
-    </p>
-
-    <p id="jt">If you are not familiar with the Java language generally,
-    then the best starting point is
-    <a href="http://java.sun.com/docs/books/tutorial/index.html"><strong>The Java Tutorial</strong></a>.
-    This overlaps with the Java Web Services Tutorial in some places, but the two work well together.
-    </p>
-
-      <p>
-          For more about building Java application in general, see the
-          <a href="http://developer.java.sun.com/developer/onlineTraining/new2java/divelog/part1/toc.jsp">New to
-          Java Center</a>.
-      </p>
-
-    </subsection>
-
-    <a name="http"/>
-    <subsection name="0.2 HTTP, HTML and User Agents">
-
-    <p>The World Wide Web was built over the Hypertext Transfer Protocol
-    (<a href="http://www.ietf.org/rfc/rfc2616.txt?number=2616">HTTP</a>) and the Hypertext Markup Language
-    (<a href="http://www.w3.org/MarkUp/">HTML</a>). A User Agent, like a web browser, uses HTTP to request
-     a HTML document. The browser then formats and displays the document to its user. HTTP is used to
-    transport more than HTML, but HTML is the lingua franca of the Web and web applications. </p>
-
-    <p>While building web applications, some Java developers will write their own HTML. Others leave that responsibility to the
-    page designers.</p>
-
-    <p>For more about HTTP, HTML, and User Agents, see:</p>
-
-    <ul>
-    <li><a href="http://www.w3.org/MarkUp/Guide/"><strong>Getting started with HTML</strong></a> by Dave Raggett</li>
-    <li><a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/HTTP.html#63796">
-    <strong>HTTP Overview</strong></a> in the Java Web Services Tutorial.</li>
-    <li><a href="http://www.rfc-editor.org/rfc/rfc2616.txt"><strong>HTTP/1.1
-        </strong></a> Specification</li>
-    <li><a href="http://www.rfc-editor.org/rfc/rfc2617.txt"><strong>HTTP
-        Basic and Digest Authentication</strong></a> Specification</li>
-    <li><a href="http://www.rfc-editor.org/rfc/rfc2109.txt"><strong>State
-        Management Mechanism</strong></a> Specification (Cookies)</li>
-    </ul>
-    </subsection>
-
-    <a name="cycle"/>
-    <subsection name="0.3 The HTTP Request/Response cycle">
-
-    <p>A very important part of HTTP for the web developer is the request/response cycle. To use HTTP
-    you have to make a request. A HTTP server, like a web server, is then obliged to respond. When you
-    build your web application, you design it to react to a HTTP request by returning a HTTP response.
-    Frameworks abstract much of these nuts and bolts, but it is important to understand
-    what is happening behind the scenes. </p>
-
-    <p>If you are not familiar with the HTTP request/response cycle, we <strong>strongly</strong> recommend the
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/HTTP.html#63796">
-    HTTP Overview</a> in the Java Web Services Tutorial.
-    </p>
-
-    </subsection>
-
-    <a name="java"/>
-    <subsection name="0.4 The Java Language and Application Frameworks">
-
-    <p>The framework is written in the popular and versatile
-    <a href="http://java.sun.com/docs/books/jls/first_edition/html/index.html">Java programming language</a>.
-    Java is an object-orientated language, and the framework makes good use of many
-    object-orientated techniques.  In addition, Java natively supports the
-    concept of <em>threads</em>, which allows more than one task to be
-    performed at the same time.  A good understanding of Java, and especially
-    object-orientated programming (OOP) and threading, will help
-    you get the most out of the framework and this User Guide. </p>
-
-    <p>For more about Java and threads, see </p>
-
-    <ul>
-    <li><a href="http://java.sun.com/docs/books/tutorial/java/index.html"><strong>Learning the Java Language</strong></a> in the Java Tutorial</li>
-    <li><a href="http://java.sun.com/docs/books/tutorial/essential/threads/index.html">
-        <strong>Threads: Doing Two or More Tasks At Once</strong></a> in the Java Language
-        Tutorial</li>
-    </ul>
-
-    <p>Even if you have worked with Java and OOP before, it can also help to be aware of the
-    programming challenges specific to creating and using application frameworks. For more about application
-    frameworks, see the classic white papers</p>
-
-    <ul>
-    <li><a href="http://www.laputan.org/drc/drc.html"><strong>Designing Reusable Classes</strong></a> by Ralph E. Johnson &amp; Brian Foote</li>
-    <li><a href="http://www.cs.wustl.edu/~schmidt/CACM-frameworks.html"><strong>Object-Oriented Application Frameworks</strong></a>
-    by Mohamed Fayad and Douglas C. Schmidt</li>
-    </ul>
-
-    <p>These papers can be especially helpful if you are fact-finding or reviewing server-side
-    <a href="http://directory.google.com/Top/Computers/Programming/Languages/Java/Server-Side/Libraries_and_Frameworks/">frameworks</a>.
-    </p>
-
-    </subsection>
-
-      <a name="chain"/>
-      <subsection name="0.4.1 Chain of Responsibility">
-
-          <p>
-              A popular technique for organizing the execution of complex
-              processing flows is the "Chain of Responsibility" pattern,
-              as described (among many other places) in the classic
-              <a href="http://www.amazon.com/exec/obidos/tg/detail/-/0201633612/apachesoftwar-20/">
-              "Gang of Four" design patterns book.</a>.
-              The GoF summarizes the Chain of Responsibility pattern as
-              "Avoid coupling  the sender of a request to its receiver
-              by giving more than one object a chance to handle the request.
-              Chain the receiving objects
-              and pass the request along the chain until an object handles it."
-          </p>
-
-          <p>
-              The CoR pattern helps us keep software components loosely coupled.
-              A component can call a Chain of Responsbility,
-              without knowing what objects are on the chain or how they are
-              implemented.
-              Most importantly, we can adjust the Chain without changing
-              how callers invoke the Chain.
-              As of version 1.3,
-              the default Request Processor,
-              which acts as the framework's "kernal",
-              is a Chain of Responsiblity.
-          </p>
-
-          <p>
-              To implement its Chain, the Request Processor uses the
-              <a href="http://jakarta.apache.org/commons/chain/">
-              Chain of Responsibility </a>component in the Jakarta Commons
-              which provides a standard implementation of the CoR pattern,
-              along with various implementations of the Context and
-              Command objects used by the Chain to service a request.
-          </p>
-
-          <p>
-          For more about Chain of Responsiblity, see
-          </p>
-
-          <ul>
-              <li>
-                  <a href="http://jakarta.apache.org/commons/chain/">
-                     Jakarta Commons Chain of Responsibility </a>
-              </li>
-              <li>
-                  <a href="http://www.onjava.com/lpt/a/5671">
-                      A look at Commons Chain</a>
-              </li>
-              <li>
-                  <a href="http://www.infonoia.com/en/content.jsp?d=inf.05.06&amp;pr=1">
-                      Better Code with Struts 1.3
-                  </a>
-              </li>
-          </ul>
-
-      </subsection>
-
-    <a name="javabeans"/>
-    <subsection name="0.5 JavaBeans">
-
-    <p>Like many Java applications, most of the framework objects are designed as
-    <a href="http://java.sun.com/products/javabeans/">JavaBeans</a>. Following the JavaBean design patterns makes
-    the framework's classes easier to use -- both by Java developers and by Java development tools. </p>
-
-    <p>Although JavaBeans were first created for visual elements, these object design patterns have been found to
-    be useful as the basis for any reusable component, like those used by the framework.</p>
-
-    <p>For more about JavaBeans, see:</p>
-
-    <ul>
-    <li><a href="http://java.sun.com/products/javabeans/docs/"><strong>The
-        JavaBeans Component Architecture Documentation</strong></a> page at
-        <code>java.sun.com</code>, including a link to download the
-        <a href="http://java.sun.com/products/javabeans/docs/spec.html">
-        JavaBeans 1.01 Specification</a></li>
-    <li><a href="http://java.sun.com/docs/books/tutorial/javabeans/index.html">
-        <strong>The JavaBeans Trail</strong></a> in the Java Tutorial</li>
-    <li><a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JSPBeans.html">
-        <strong>JavaBeans Components in JSP Pages</strong></a> in the Java Web Services Tutorial
-        </li>
-    </ul>
-
-    </subsection>
-
-    <a name="reflection"/>
-    <subsection name="0.5.1 Reflection and Introspection">
-
-    <p>
-    Reflection is the process of determining which member fields and methods are available on an object.
-    Introspection is a specialized form of reflection used  by the JavaBean API.
-    Using Introspection, we can determine which methods of a JavaBean are intended to be accessed by other objects.
-    (The getters and the  setters, for example.)
-    </p>
-
-    <p>
-    The framework uses Introspection to convert HTTP parameters into JavaBean properties and to populate HTML fields from JavaBean properties.
-    This technique makes it easy to "roundtrip" properties between HTML forms and JavaBeans.
-    </p>
-
-    <p>
-    For more about Reflection and Introspection, see
-    </p>
-
-    <ul>
-    <li>
-    <a href="http://java.sun.com/docs/books/tutorial/reflect/">The Reflection Trail</a>
-    </li>
-    <li>
-    <a href="http://java.sun.com/products/javabeans/docs/spec.html">Chapter 8 of the JavaBeans API Specification</a>
-    </li>
-    </ul>
-
-    </subsection>
-
-    <a name="maps"/>
-    <subsection name="0.5.2 Maps">
-
-    <p>
-    JavaBeans store data as properties and may act on that data through other methods.
-    JavaBeans are flexible and powerful objects but are not the only object that programmers use to store data.
-    Another popular object is the Map [<code>java.util.Map</code>].
-    A Map is a simple collection of name and value pairs.
-    Maps are often used "behind the scenes" as a flexible way to store dynamic data.
-    </p>
-
-    </subsection>
-
-    <a name="dynabeans"/>
-    <subsection name="0.5.3 DynaBeans">
-
-    <p>
-    DynaBeans combine the extensibility of JavaBeans with the flexibility of a Map.
-    Defining even the simplest JavaBean requires defining a new class and coding a field and two methods for each property.
-    The properties of a DynaBean can be configured via an XML descriptor.
-    The virtual properties of a DynaBean can't be called by standard Java methods,
-    but work well with components that rely on reflection and introspection.
-    </p>
-
-    <p>
-    In your application, you can use DynaBeans to describe your HTML forms.
-    This strategy can avoid creating a formal JavaBean subclass to store a few simple properties.
-    </p>
-
-    <p>
-    For more about DynaBeans, see
-    </p>
-
-    <ul>
-    <li>
-    The Commons BeanUtils
-    <a href="http://jakarta.apache.org/commons/beanutils/api/org/apache/commons/beanutils/package-summary.html#package_description">
-    Package Description</a> and <a href="http://jakarta.apache.org/commons/beanutils/api/index.html">Javadocs</a>.
-    </li>
-     <li>
-         <a href="https://formdef.dev.java.net/">Struts FormDef</a>
-     </li>
-    </ul>
-
-    </subsection>
-
-    <a name="resources"/>
-    <subsection name="0.6 Properties Files and ResourceBundles">
-
-    <p>Java applications, including web applications, are often configured using
-    <a href="http://java.sun.com/j2se/1.4.1/docs/api/java/util/Properties.html">Properties</a>
-    files. Properties files are the basis for the
-    <a href="http://java.sun.com/j2se/1.4.1/docs/api/java/util/ResourceBundle.html">ResourceBundles</a> that the framework uses to provide message resources
-    to an application. </p>
-
-    <p>For more about Properties files, see: </p>
-
-    <ul>
-    <li><a href="http://java.sun.com/docs/books/tutorial/essential/attributes/properties.html">
-    <strong>Using Properties to Manage Program Attributes</strong></a> in The Java Tutorial</li>
-    </ul>
-
-    <p>Java ResourceBundles use one or more Properties files to provide internationalized messages
-    to users based their
-    <a href="http://java.sun.com/j2se/1.4.1/docs/api/java/util/Locale.html">Locale</a>.
-    Support for localizing an application was built into the framework from the ground-up.</p>
-
-    <p>For more about localization and ResourceBundles, see </p>
-
-    <ul>
-    <li><a href="http://java.sun.com/docs/books/tutorial/i18n/resbundle/concept.html"><strong>About the ResourceBundle Class</strong></a>
-    in the Java Tutorial</li>
-    </ul>
-
-    </subsection>
-
-    <a name="servlets"/>
-    <subsection name="0.7 Java Servlets">
-    <p>
-    Since Java is an object-orientated language, the
-    <a href="http://www.novocode.com/doc/servlet-essentials/">Java Servlet</a>
-    platform strives to cast HTTP into an object-orientated form.
-    This strategy makes it easier for Java developers to concentrate on what they need their application to do --
-    rather than the mechanics of HTTP.
-    </p>
-
-    <p>
-    HTTP provides a standard mechanism for extending servers called the Common Gateway Interface, or CGI.
-    The server can pass a request to a CGI-aware program, and the program will pass back a response.
-    Likewise, a Java-aware server can pass a request to a servlet container.
-    The container can fulfill the request or it can pass the request back to the HTTP server.
-    The container decides whether it can handle the request by checking its list of servlets.
-    If there is a servlet registered for the request, the container passes the request to the servlet.
-    </p>
-
-    <p>
-    When a request comes in, the container checks to see if there is a servlet registered for that request.
-    If there is a match,
-    the request is given to the servlet.
-    If not, the request is returned to the HTTP server.
-    </p>
-
-    <p>
-    It's the container's job to manages the servlet lifecycle.
-    The container creates the servlets, invokes the servlets, and ultimately disposes the servlets.
-    </p>
-
-    <p>
-    A servlet is generally a subclass of <code>javax.servlet.http.HttpServlet</code>.
-    A servlet must implement four methods, which are invoked by the container as needed:
-    </p>
-
-      <ul>
-      <li><strong>public void init(ServletConfig config)</strong> - Called by the
-          servlet container when the servlet instance is first created, and
-          before any request is processed.</li>
-      <li><strong>public void doGet(HttpServletRequest request,
-          HttpServletResponse response)</strong> - Called to process a
-          specific request received using the HTTP <code>GET</code> protocol,
-          which generates a corresponding dynamic response.</li>
-      <li><strong>public void doPost(HttpServletRequest request,
-          HttpServletResponse response)</strong> - Called to process a
-          specific request received using the HTTP <code>POST</code> protocol,
-          which generates a corresponding dynamic response.</li>
-      <li><strong>public void destroy()</strong> - Called by the servlet
-          container when it takes this servlet instance out of service,
-          such as when a web application is being undeployed or when the
-          entire container is being shut down.</li>
-      </ul>
-
-    <p>
-    The framework provides a ready-to-use servlet for your application [<code>org.apache.struts.action.ActionServlet</code>].
-    As a Struts developer, you can then just write objects that the Struts ActionServlet calls when needed.
-    But it is still helpful to understand the basics of what servlets are,
-    and the role they play in a Java web application.
-    </p>
-
-    <p>
-    For more about Java Servlets, see:
-    </p>
-
-    <ul>
-    <li><a href="http://java.sun.com/products/servlet/"><strong>The
-        Java Servlet Technology</strong></a> page at
-        <code>java.sun.com</code></li>
-    <li><a href="http://java.sun.com/products/servlet/download.html"><strong>The
-        Servlet 2.2 and 2.3 Specifications</strong></a> download page at
-        <code>java.sun.com</code></li>
-    <li><a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets.html">
-        <strong>Java Servlet Technology</strong></a> in the Java Web Services Tutorial.</li>
-    <li><a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/WebApp.html">
-        <strong>Web Applications</strong></a> in the Java Web Services Tutorial.</li>
-    </ul>
-
-    </subsection>
-
-    <a name="threads"/>
-    <subsection name="0.7.1 Servlets and threads">
-
-    <p>
-    To boost performance, the container can multi-thread servlets.
-    Only one instance of a particular servlet is created,
-    and each request for that servlet passes through the same object.
-    This strategy helps the container make the best use of available resources.
-    The tradeoff is that the servlet's <code>doGet()</code> and <code>doPost()</code> methods must be programmed in a <em>thread-safe</em> manner.
-    </p>
-
-    <p>
-    For more about servlets and thread-safety, see:
-    </p>
-
-    <ul>
-    <li>
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets5.html#64386">Controlling Concurrent Access to Shared Resources</a> in Java Web Services Tutorial.
-    </li>
-    </ul>
-
-    </subsection>
-
-      <a name="context"/>
-      <subsection name="0.7.2 Servlet Context">
-
-      <p>The <em>ServletContext</em> interface [<code>javax.servlet.ServletContext</code>] defines a servlet's view of
-      the web application within which the servlet is running.  It is
-      accessible in a servlet via the <code>getServletConfig()</code> method,
-      and in a JSP page as the <code>application</code> implicit variable.
-      Servlet contexts provide several APIs that are very useful in building
-      Struts based web applications:</p>
-      <ul>
-      <li><em>Access To Web Application Resources</em> - A servlet can
-          access static resource files within the web application using the
-          <code>getResource()</code> and <code>getResourceAsStream()</code>
-          methods.</li>
-      <li><em>Servlet Context Attributes</em> - The context makes available
-          a storage place for Java objects, identified by string-valued keys.
-          These attributes are global to the entire web application, and may
-          be accessed by a servlet using the <code>getAttribute()</code>,
-          <code>getAttributeNames()</code>, <code>removeAttribute()</code>, and
-          <code>setAttribute()</code> methods.  From a JSP page, servlet
-          context attributes are also known as "application scope beans".
-          </li>
-      </ul>
-
-    <p>
-    For more about the servlet context, see:
-    </p>
-
-    <ul>
-    <li>
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets10.html#64724">Accessing the Web Context</a> in Java Web Services Tutorial.
-    </li>
-    </ul>
-
-      </subsection>
-
-      <a name="request"/>
-      <subsection name="0.7.3 Servlet Request">
-
-      <p>Each request processed by a servlet is represented by a Java
-      interface, normally a <code>HttpServletRequest</code>
-      [<code>javax.servlet.http.HttpServletRequest</code>].
-      The request interface provides an object-oriented mechanism to access
-      all of the information that was included in the underlying HTTP request,
-      including:</p>
-      <ul>
-      <li><em>Cookies</em> - The set of cookies included with this request
-          are available via the <code>getCookies()</code> method.</li>
-      <li><em>Headers</em> - HTTP headers that were included with
-          the request are accessible by name. You can enumerate the names
-          of all included headers.</li>
-      <li><em>Parameters</em> - Request parameters, including those from
-          the query string portion of the URL and from the embedded content
-          of the request (POST only) are available by name.</li>
-      <li><em>Request Characteristics</em> - Many other characteristics
-          of the incoming HTTP request, such as the method used (normally
-          GET or POST) the protocol scheme used ("http" or "https"), and
-          similar values.</li>
-      <li><em>Request URI Information</em> - The original request URI
-          being processed is available via <code>getRequestURI()</code>.
-          In addition, the constituent parts into which the servlet container
-          parses the request URI (contextPath, servletPath, and pathInfo) are
-          available separately.</li>
-      <li><em>User Information</em> - If you are using
-          <a href="#security">Container Managed Security</a>, you can ask for
-          the username of the authenticated user, retrieve a
-          <code>Principal</code> object representing the current user, and
-          whether the current user is authorized for a specified role.</li>
-      </ul>
-
-      <p>In addition, servlet requests support <em>request attributes</em>
-      (from JSP, these are "request scope beans"), analogous to the servlet
-      context attributes described above. Request attributes are often used
-      to communicate state information from a business logic class that
-      generates it to a view component (such as a JSP page) that will use
-      the information to produce the corresponding response.</p>
-
-      <p>The servlet container guarantees that a particular request will
-      be processed by a servlet on a single thread. Therefore, you do not
-      generally have to worry about the thread safety of your access to
-      request properties and attributes.</p>
-
-    <p>
-    For more about the servlet request, see:
-    </p>
-
-    <ul>
-    <li>
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets7.html#64433">Getting Information from Requests</a> in Java Web Services Tutorial.
-    </li>
-    </ul>
-
-      </subsection>
-
-      <a name="response"/>
-      <subsection name="0.7.4 Servlet Response">
-
-      <p>The primary purpose of a servlet is to process an incoming
-      <a href="#request">Servlet Request</a> [<code>javax.servlet.http.HttpServletRequest</code>]
-      and convert it into a
-      corresponding response. This is performed by calling appropriate
-      methods on the servlet response [<code>javax.servlet.http.HttpServletResponse</code>]
-      interface. Available methods let you:</p>
-      <ul>
-      <li><em>Set Headers</em> - You can set HTTP headers that will be
-          included in the response.  The most important header is the
-          <code>Content-Type</code> header, which tells your client what
-          kind of information is included in the body of this response.
-          This is typically set to <code>text/html</code> for an HTML page,
-          or <code>text/xml</code> for an XML document.</li>
-      <li><em>Set Cookies</em> - You can add cookies to the current
-          response.</li>
-      <li><em>Send Error Responses</em> - You can send an HTTP error status
-          (instead of a usual page of content) using
-          <code>sendError()</code>.</li>
-      <li><em>Redirect To Another Resource</em> - You can use the
-          <code>sendRedirect()</code> method to redirect the client to
-          some other URL that you specify.</li>
-      </ul>
-
-      <p>An important principle in using the servlet response APIs is that
-      any methods you call to manipulate headers or cookies
-      <strong>MUST</strong> be performed before the first buffer-full of
-      content has been flushed to the client. The reason for this restriction
-      is that such information is transmitted at the beginning of the HTTP
-      response, so trying things like adding a header after the headers have
-      already been sent will not be effective.</p>
-
-      <p>
-      When you are using presentation pages in a Model 2 application,
-      you will not generally use the servlet response APIs directly.
-      In the case of JavaServerPages, the JSP page compiler
-      in your servlet container will convert your page into a servlet.
-      The JSP servlet renders the response, interspersing dynamic
-      information where you have interposed JSP custom tags.
-      </p>
-
-      <p>
-      Other presentation systems, like Velocity Tools for Struts,
-      may delegate rendering the response to a specialized servlet,
-      but the same pattern holds true.
-      You create a template,
-      and the dynamic response is generated automatically from the template.
-      </p>
-
-    <p>
-    For more about the servlet response, see:
-    </p>
-
-    <ul>
-    <li>
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets7.html#64531">Constructing Responses</a> in Java Web Services Tutorial.
-    </li>
-    </ul>
-
-      </subsection>
-
-      <a name="filter"/>
-      <subsection name="0.7.5 Filtering">
-
-      <p>If you are using a servlet container based on version
-      <strong>2.3</strong> or later of the Servlet Specification (such as
-      Tomcat 4.x), you can take advantage of the new Filter APIs
-      [<code>javax.servlet.Filter</code>] that
-      let you compose a set of components that will process a request or
-      response. Filters are aggregated into a chain in which each filter
-      has a chance to process the request and response before and after
-      it is processed by subsequent filters (and the servlet that is ultimately
-      called).</p>
-
-      <p>The Struts 1.0, 1.1, and 1.2 versions require only version 2.2 or later
-      of the Servlet Specification to be implemented by your servlet container,
-      so those versions do not use Filters. Beginning with the 
-      1.3 version, a container that supports version 2.3 or later of the Servlet
-      Specification is required, and it is possible that the framework might use
-      Filters in the future.</p>
-      
-      <p>
-      For more about filters, see:
-      </p>
-
-    <ul>
-    <li>
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets8.html#64572">Filtering Requests and Responses</a>
-    </li>
-    </ul>
-
-      </subsection>
-
-      <a name="session"/>
-      <subsection name="0.7.6 Sessions">
-
-      <p>One of the key characteristics of HTTP is that it is
-      <em>stateless</em>. In other words, there is nothing built in to
-      HTTP that identifies a subsequent request from the same user as being
-      related to a previous request from that user. This makes building an
-      application that wants to engage in a conversation with the user over
-      several requests to be somewhat difficult.</p>
-
-      <p>To alleviate this difficulty, the servlet API provides a programmatic
-      concept called a <em>session</em>, represented as an object that
-      implements the <code>javax.servlet.http.HttpSession</code> interface.
-      The servlet container will use one of two techniques (cookies or
-      URL rewriting) to ensure that the next request from the same user will
-      include the <em>session id</em> for this session, so that state
-      information saved in the session can be associated with multiple
-      requests. This state information is stored in <em>session
-      attributes</em> (in JSP, they are known as "session scope beans").</p>
-
-      <p>To avoid occupying resources forever when a user fails to complete
-      an interaction, sessions have a configurable <em>timeout interval</em>.
-      If the time gap between two requests exceeds this interval, the session
-      will be timed out, and all session attributes removed. You define a
-      default session timeout in your web application deployment descriptor,
-      and you can dynamically change it for a particular session by calling
-      the <code>setMaxInactiveInterval()</code> method.</p>
-
-      <p>Unlike requests, you need to be concerned about thread safety on
-      your session attributes (the methods these beans provide, not the
-      <code>getAttribute()</code> and <code>setAttribute()</code> methods
-      of the session itself). It is surprisingly easy for there to be
-      multiple simultaneous requests from the same user, which will therefore
-      access the same session.</p>
-
-      <p>Another important consideration is that session attributes occupy
-      memory in your server <em>in between</em> requests. This can have
-      an impact on the number of simultaneous users that your application can
-      support. If your application requirements include very large numbers of
-      simultaneous users, you will likely want to minimize your use of
-      session attributes, in an effort to control the overall amount of memory
-      required to support your application.</p>
-
-      <p>
-      For more about sessions, see:
-      </p>
-      <ul>
-        <li>
-        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets11.html#64744">Maintaining Client State</a> in Java Web Services Tutorial
-        </li>
-        <li>
-        <a href="http://java.sun.com/products/servlet/2.1/api/javax.servlet.http.HttpSession.html"><code>javax.servlet.http.HttpSession</code></a>
-        </li>
-      </ul>
-
-      </subsection>
-
-      <a name="dispatch"/>
-      <subsection name="0.7.7 Dispatching Requests">
-
-      <p>
-      The Java Servlet specification extends the HTTP request/response cycle by allowing the request to be dispatched,
-      or forwarded, between resources.
-      The framework uses this feature to pass a request through specialized components,
-      each handling one aspect of the response.
-      In the normal course, a request may pass through a controller object, a model object,
-      and finally to a view object as part of a single request/response cycle.
-      </p>
-
-      </subsection>
-
-      <a name="webapp"/>
-      <subsection name="0.7.8 Web Applications">
-
-      <p>
-      Just as a HTTP server can be used to host several distinct web sites,
-      a servlet container can be used to host more than one web application.
-      The Java servlet platform provides a well-defined mechanism for organizing and deploying web applications.
-      Each application runs in its own namespace so that they can be developed and deployed separately.
-      A web application can be assembled into a Web Application Archive, or WAR file.
-      The single WAR can be uploaded to the server and automatically deployed.
-      </p>
-
-    <p>
-    For more about web applications, see:
-    </p>
-    <ul>
-    <li>
-        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/WebApp.html#76431">Web Applications</a> in Java Web Services Tutorial
-    </li>
-    </ul>
-
-      </subsection>
-
-      <a name="events"/>
-      <subsection name="0.7.9 Web application deployment descriptor (web.xml)">
-
-      <p>
-      Most aspects of an application's lifecycle are configured through an XML document called the Web application deployment descriptor.
-      The schema of the descriptor, or web.xml, is given by the Java servlet specification.
-      </p>
-
-      <p>
-      For more about the web.xml and application lifecycle events, see:
-      </p>
-      <ul>
-      <li>
-      <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/WebApp2.html#64550">Web Application Life Cycle</a> in Java Web Services Tutorial
-      </li>
-      </ul>
-
-      </subsection>
-
-    <a name="security"/>
-    <subsection name="0.7.10 Security" href="">
-
-    <p>
-    One detail that can be configured in the Web application deployment descriptor is container-managed security.
-    Declarative security can be used to protect requests for URIs that match given patterns.
-    Pragmatic security can be used to fine-tune security make authorization decisions based on the time of day,
-    the parameters of a call, or the internal state of a Web component.
-    It can also be used to restrict authentication based on information in a database.
-    </p>
-
-      <p>For more information about container-managed security, see:</p>
-      <ul>
-      <li><a href="http://java.sun.com/webservices/docs/1.2/tutorial/doc/index.html">
-          Web Application Security (Chapter 24)</a> in the Java Web Services Tutorial
-      </li>
-      </ul>
-
-    </subsection>
-
-    <a name="jsp"/>
-    <subsection name="0.8 JavaServer Pages, JSP Tag Libraries, and JavaServer Faces" href="">
-    <p><a href="http://java.sun.com/products/jsp/product.html">JavaServer Pages</a> (JSPs) are
-    "inside-out servlets" that make it easier to create and maintain dynamic web pages. Instead
-    of putting what you want to write to the HTTP response inside of a Java <code>print</code>
-    statement, everything in a JavaServer Page is written to the response, <strong>except</strong> what is
-    placed within special Java statements.</p>
-
-    <p>With <strong>JavaServer Pages</strong> you can start by writing the page in standard HTML and then add the
-    dynamic features using statements in the Java language or by using
-    <a href="http://java.sun.com/products/jsp/taglibraries.html">JSP tags</a>.
-    The Struts Classic distribution includes several JSP tags that make it easy to access the framework's
-    features from a JavaServer Page.</p>
-
-    <p>For more about JavaServer Pages and Custom JSP Tag Libraries see  </p>
-
-    <ul>
-    <li><a href="http://java.sun.com/products/jsp/"><strong>The
-        JavaServer Pages Technology</strong></a> page at
-        <code>java.sun.com</code></li>
-    <li><a href="http://java.sun.com/products/jsp/download.html"><strong>The
-        JSP 1.1 and 1.2 Specifications</strong></a> download page at
-        <code>java.sun.com</code></li>
-    <li><a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JSPIntro.html"><strong>JavaServer Pages Technology</strong></a> in the Java Web Services Tutorial</li>
-    <li><a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JSPTags.html"><strong>Custom Tags in JSP Pages</strong></a> in the Java Web Services Tutorial</li>
-    </ul>
-
-    <p>Many times, JSP tags work hand-in-hand with JavaBeans. The application sends a JavaBean to
-    the JSP, and the JSP tag uses the bean to customize the page for the instant user. For more, see
-    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JSPBeans.html">JavaBeans Components in JSP Pages</a>
-    in the Java Web Services Tutorial.</p>
-
-    <p>The framework also works well with the
-    <a href="http://java.sun.com/products/jsp/jstl"><strong>JavaServer Pages Standard Tag Library</strong></a>
-    (JSTL) and taglibs from other sources, like
-    <a href="http://jsptags.com/">JSP Tags</a>,
-    <a href="http://jakarta.apache.org/taglibs/index.html">Jakarta Taglibs</a>,
-    <a href="http://struts.application-servers.com">Struts Layout</a>, and
-    <a href="http://http://displaytag.sourceforge.net/">Display Tags</a>.
-    </p>
-
-    <p>
-        One of the subprojects available for Struts Classic is <a href="http://struts.apache.org/struts-el/index.html">Struts-EL</a>.
-        This taglib is specifically designed to work well with JSTL.
-        In particular, it uses the same "expression language" engine for evaluating tag attribute values as JSTL.
-        This is in contrast to the original Struts tag library, which can only use "rtexprvalue"s (runtime scriptlet
-        expressions) for dynamic attribute values.
-    </p>
-
-    <p>There are also toolkits available that make the framework easy to use with
-    <a href="http://stxx.sourceforge.net/">XSLT</a> and
-    <a href="http://jakarta.apache.org/velocity/tools/index.html">Velocity Templates</a>.
-    </p>
-
-        <p>
-            The newest star on the Java horizon is  <a href="http://java.sun.com/j2ee/javaserverfaces/">JavaServer Faces technology</a>.
-            JSF simplifies building user interfaces for JavaServer applications, both for the web and for the desktop.
-            To keep pace, Apache Struts is offering a new framework to go with this new technology, called
-            <a href="http://struts.apache.org/struts-shale/index.html">Struts Shale</a>.
-            For teams looking for a smoother transition to JSF, we offer Struts-Faces taglib,
-            which lets you use JSF components with your existing Actions.
-        </p>
-        <p>
-            For an open source implementation of JSF, visit our sibling project
-           .
-        </p>
-
-        <p>For more about JSTL and JavaServer Faces see  </p>
-
-       <ul>
-           <li>
-               <a href="http://today.java.net/pub/a/today/2003/10/07/jstl1.html">Practical JSTL, Part 1</a>
-               by Sue Spielman
-           </li>
-           <li>
-               <a href="http://www.jsfcentral.com"><strong>JSF Central</strong></a> - JavaServer Faces resources.
-            </li>
-           <li>
-               <a href="http://www.jamesholmes.com/JavaServerFaces/"><strong>JavaServer Faces Resources</strong></a>
-            - James Holmes dot Com.
-           </li>
-           <li> <a href="http://myfaces.apache.org">Apache MyFaces</a> - An open source implementation of
-               the JSF specification.
-           </li>
-       </ul>
-
-    </subsection>
-
-    <a name="xml"/>
-    <subsection name="0.9 Extensible Markup Language (XML)" href="">
-
-    <p>The features provided by the framework rely on a number of objects that are
-    usually deployed using a configuration file written in
-    <a href="http://www.w3.org/XML/">Extensible Markup Language</a>. XML is also used to
-    configure Java web applications; so, this is yet another familiar approach.
-    </p>
-
-    <p>For more about XML configuration files and Java web applications, see</p>
-
-    <ul>
-    <li>
-        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/WebApp4.html#64678">Configuring Web
-        Applications</a> in the Java Web Services Tutorial</li>
-    </ul>
-
-    <p>
-        For more about how XML is used with Java applications generally, see
-        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JAXPIntro.html">Java API for XML Processing</a>
-        in the Java Web Services Tutorial.
-        While the framework makes good use of this API internally, it is not something most Struts developers would use
-        when writing their own applications.
-    </p>
-
-    </subsection>
-        <a name="descriptors"/>
-        <subsection name="0.9.1 Descriptors" href="descriptors">
-
-        <p>
-        When Java applications use XML configuration files,
-        the elements are most often used as <em>descriptors</em>.
-        The application does not use the XML elements directly.
-        The elements are used to create and configure (or deploy) Java objects.
-        </p>
-
-        <p>
-        The Java Servlet platform uses an XML configuration file to deploy servlets (among other things).
-        Likewise, The framework uses an XML configuration file to deploy objects.
-        </p>
-
-    </subsection>
-
-      <a name="jaas"/>
-      <subsection name="0.10 JAAS" href="">
-
-      <p>
-          While the framework can work with any approach to user authentication and authorization, Struts 1.1 and later offers
-          direct support for the standard Java Authentication and Authorization Service (JAAS).
-          You can now specify security roles on an action-by-action basis.
-      </p>
-
-      <p>For more about JAAS, see the Sun Developer Network
-      <a href="http://java.sun.com/products/jaas">product page</a>
-      and the <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/WebAppSecurity.html">
-      Web Application Security</a> chapter of the
-      <a href="http://java.sun.com/webservices/docs/1.0/tutorial/index.html">Java Web Services Tutorial</a>.</p>
-
-      <p>
-          A popular extension for handling security in a Java web application, including a framework application,
-          is <a href="http://securityfilter.sourceforge.net/">SecurityFilter</a>.
-      </p>
-    </subsection>
-
-    <a name="layers"/>
-    <subsection name="0.11 Other layers">
-
-    <p>
-       The framework provides the control layer for a web application.
-       Developers can use this layer with other standard technologies
-       to provide the business, data access, and presentation layers.
-    </p>
-
-    <p>
-       For more about creating business and data access layers,
-       see the "<a href="building_model.html">Building Model Components</a>"
-       section.
-    </p>
-
-    <p>
-      For more about creating the presentation layer,
-      see the "<a href="building_model.html">Building View Components</a>"
-      section.
-    </p>
-
-    </subsection>
-
-</section>
-
-<section>
-    <p class="right">
-    Next: <a href="introduction.html">Introduction</a>
-    </p>
-</section>
+    <properties>
+        <title>Preface: Key Technologies</title>
+    </properties>
+
+    <body>
+
+        <section name="0. Preface: Key Technologies">
+
+            <a name="suspects"/>
+            <subsection name="0.1 The Usual Suspects">
+
+                <p>
+                    This User Guide is written for active web developers and
+                    assumes a working
+                    knowledge about how Java web applications are built.
+                    Before getting started, you should
+                    understand the basics of several key technologies:
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="#http">HTTP, HTML, and User Agents</a>
+                    </li>
+                    <li>
+                        <a href="#cycle">The HTTP Request/Response Cycle</a>
+                    </li>
+                    <li>
+                        <a href="#java">The Java Language and Application
+                            Frameworks</a>
+                    </li>
+                    <li>
+                        <a href="#javabeans">JavaBeans</a>
+                    </li>
+                    <li>
+                        <a href="#resources">Properties Files and
+                            ResourceBundles</a>
+                    </li>
+                    <li>
+                        <a href="#servlets">Java Servlets</a>
+                    </li>
+                    <li>
+                        <a href="#jsp">JavaServer Pages and JSP Tag
+                            Libraries</a>
+                    </li>
+                    <li>
+                        <a href="#xml">Extensible Markup Language</a>
+                    </li>
+                    <li>
+                        <a href="#jaas">JAAS</a>
+                    </li>
+                    <li>
+                        <a href="#layers">Other Layers</a>
+                    </li>
+                </ul>
+
+                <p>
+                    This chapter briefly defines each of these technologies
+                    but does not describe them in detail.
+                    For your convenience, links to further information are
+                    provided if you would like to learn more about a
+                    technology.
+                </p>
+
+                <p id="JavaWebServicesTutorial">If you are familiar with Java,
+                    but not these technologies,
+                    the best overall starting point is
+                    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/index.html">
+                        <strong>The Java Web Services Tutorial</strong>
+                    </a>
+                    .
+                    This document is also available for download in
+                    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JavaWSTutorial.pdf">
+                        PDF</a>
+                    format.
+                </p>
+
+                <p>If you've created web applications for other platforms, you
+                    may be able to follow along
+                    and visit the other references as needed. The core
+                    technologies used by the framework are
+                    also used by most other Java web development products, so
+                    the background information will be
+                    useful in any Java project.
+                </p>
+
+                <p id="jt">If you are not familiar with the Java language
+                    generally,
+                    then the best starting point is
+                    <a href="http://java.sun.com/docs/books/tutorial/index.html">
+                        <strong>The Java Tutorial</strong>
+                    </a>
+                    .
+                    This overlaps with the Java Web Services Tutorial in some
+                    places, but the two work well together.
+                </p>
+
+                <p>
+                    For more about building Java application in general, see
+                    the
+                    <a href="http://developer.java.sun.com/developer/onlineTraining/new2java/divelog/part1/toc.jsp">
+                        New to
+                        Java Center</a>
+                    .
+                </p>
+
+            </subsection>
+
+            <a name="http"/>
+            <subsection name="0.2 HTTP, HTML and User Agents">
+
+                <p>The World Wide Web was built over the Hypertext Transfer
+                    Protocol
+                    (
+                    <a href="http://www.ietf.org/rfc/rfc2616.txt?number=2616">
+                        HTTP</a>
+                    ) and the Hypertext Markup Language
+                    (
+                    <a href="http://www.w3.org/MarkUp/">HTML</a>
+                    ). A User Agent, like a web browser, uses HTTP to request
+                    a HTML document. The browser then formats and displays the
+                    document to its user. HTTP is used to
+                    transport more than HTML, but HTML is the lingua franca of
+                    the Web and web applications.
+                </p>
+
+                <p>While building web applications, some Java developers will
+                    write their own HTML. Others leave that responsibility to
+                    the
+                    page designers.</p>
+
+                <p>For more about HTTP, HTML, and User Agents, see:</p>
+
+                <ul>
+                    <li>
+                        <a href="http://www.w3.org/MarkUp/Guide/">
+                            <strong>Getting started with HTML</strong>
+                        </a>
+                        by Dave Raggett
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/HTTP.html#63796">
+                            <strong>HTTP Overview</strong>
+                        </a>
+                        in the Java Web Services Tutorial.
+                    </li>
+                    <li>
+                        <a href="http://www.rfc-editor.org/rfc/rfc2616.txt">
+                            <strong>HTTP/1.1
+                            </strong>
+                        </a>
+                        Specification
+                    </li>
+                    <li>
+                        <a href="http://www.rfc-editor.org/rfc/rfc2617.txt">
+                            <strong>HTTP
+                                Basic and Digest Authentication</strong>
+                        </a>
+                        Specification
+                    </li>
+                    <li>
+                        <a href="http://www.rfc-editor.org/rfc/rfc2109.txt">
+                            <strong>State
+                                Management Mechanism</strong>
+                        </a>
+                        Specification (Cookies)
+                    </li>
+                </ul>
+            </subsection>
+
+            <a name="cycle"/>
+            <subsection name="0.3 The HTTP Request/Response cycle">
+
+                <p>A very important part of HTTP for the web developer is the
+                    request/response cycle. To use HTTP
+                    you have to make a request. A HTTP server, like a web
+                    server, is then obliged to respond. When you
+                    build your web application, you design it to react to a
+                    HTTP request by returning a HTTP response.
+                    Frameworks abstract much of these nuts and bolts, but it
+                    is important to understand
+                    what is happening behind the scenes.</p>
+
+                <p>If you are not familiar with the HTTP request/response
+                    cycle, we
+                    <strong>strongly</strong>
+                    recommend the
+                    <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/HTTP.html#63796">
+                        HTTP Overview</a>
+                    in the Java Web Services Tutorial.
+                </p>
+
+            </subsection>
+
+            <a name="java"/>
+            <subsection
+                    name="0.4 The Java Language and Application Frameworks">
+
+                <p>The framework is written in the popular and versatile
+                    <a href="http://java.sun.com/docs/books/jls/first_edition/html/index.html">
+                        Java programming language</a>
+                    .
+                    Java is an object-orientated language, and the framework
+                    makes good use of many
+                    object-orientated techniques. In addition, Java natively
+                    supports the
+                    concept of
+                    <em>threads</em>
+                    , which allows more than one task to be
+                    performed at the same time. A good understanding of Java,
+                    and especially
+                    object-orientated programming (OOP) and threading, will
+                    help
+                    you get the most out of the framework and this User Guide.
+                </p>
+
+                <p>For more about Java and threads, see</p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/docs/books/tutorial/java/index.html">
+                            <strong>Learning the Java Language</strong>
+                        </a>
+                        in the Java Tutorial
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/docs/books/tutorial/essential/threads/index.html">
+                            <strong>Threads: Doing Two or More Tasks At
+                                Once</strong>
+                        </a>
+                        in the Java Language
+                        Tutorial
+                    </li>
+                </ul>
+
+                <p>Even if you have worked with Java and OOP before, it can
+                    also help to be aware of the
+                    programming challenges specific to creating and using
+                    application frameworks. For more about application
+                    frameworks, see the classic white papers</p>
+
+                <ul>
+                    <li>
+                        <a href="http://www.laputan.org/drc/drc.html">
+                            <strong>Designing Reusable Classes</strong>
+                        </a>
+                        by Ralph E. Johnson &amp; Brian Foote
+                    </li>
+                    <li>
+                        <a href="http://www.cs.wustl.edu/~schmidt/CACM-frameworks.html">
+                            <strong>Object-Oriented Application
+                                Frameworks</strong>
+                        </a>
+                        by Mohamed Fayad and Douglas C. Schmidt
+                    </li>
+                </ul>
+
+                <p>These papers can be especially helpful if you are
+                    fact-finding or reviewing server-side
+                    <a href="http://directory.google.com/Top/Computers/Programming/Languages/Java/Server-Side/Libraries_and_Frameworks/">
+                        frameworks</a>
+                    .
+                </p>
+
+            </subsection>
+
+            <a name="chain"/>
+            <subsection name="0.4.1 Chain of Responsibility">
+
+                <p>
+                    A popular technique for organizing the execution of
+                    complex
+                    processing flows is the "Chain of Responsibility" pattern,
+                    as described (among many other places) in the classic
+                    <a href="http://www.amazon.com/exec/obidos/tg/detail/-/0201633612/apachesoftwar-20/">
+                        "Gang of Four" design patterns book.</a>
+                    .
+                    The GoF summarizes the Chain of Responsibility pattern as
+                    "Avoid coupling the sender of a request to its receiver
+                    by giving more than one object a chance to handle the
+                    request.
+                    Chain the receiving objects
+                    and pass the request along the chain until an object
+                    handles it."
+                </p>
+
+                <p>
+                    The CoR pattern helps us keep software components loosely
+                    coupled.
+                    A component can call a Chain of Responsbility,
+                    without knowing what objects are on the chain or how they
+                    are
+                    implemented.
+                    Most importantly, we can adjust the Chain without changing
+                    how callers invoke the Chain.
+                    As of version 1.3,
+                    the default Request Processor,
+                    which acts as the framework's "kernal",
+                    is a Chain of Responsiblity.
+                </p>
+
+                <p>
+                    To implement its Chain, the Request Processor uses the
+                    <a href="http://jakarta.apache.org/commons/chain/">
+                        Chain of Responsibility</a>
+                    component in the Jakarta Commons
+                    which provides a standard implementation of the CoR
+                    pattern,
+                    along with various implementations of the Context and
+                    Command objects used by the Chain to service a request.
+                </p>
+
+                <p>
+                    For more about Chain of Responsiblity, see
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://jakarta.apache.org/commons/chain/">
+                            Jakarta Commons Chain of Responsibility</a>
+                    </li>
+                    <li>
+                        <a href="http://www.onjava.com/lpt/a/5671">
+                            A look at Commons Chain</a>
+                    </li>
+                    <li>
+                        <a href="http://www.infonoia.com/en/content.jsp?d=inf.05.06&amp;pr=1">
+                            Better Code with Struts 1.3
+                        </a>
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="javabeans"/>
+            <subsection name="0.5 JavaBeans">
+
+                <p>Like many Java applications, most of the framework objects
+                    are designed as
+                    <a href="http://java.sun.com/products/javabeans/">
+                        JavaBeans</a>
+                    . Following the JavaBean design patterns makes
+                    the framework's classes easier to use -- both by Java
+                    developers and by Java development tools.
+                </p>
+
+                <p>Although JavaBeans were first created for visual elements,
+                    these object design patterns have been found to
+                    be useful as the basis for any reusable component, like
+                    those used by the framework.</p>
+
+                <p>For more about JavaBeans, see:</p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/products/javabeans/docs/">
+                            <strong>The
+                                JavaBeans Component Architecture
+                                Documentation</strong>
+                        </a>
+                        page at
+                        <code>java.sun.com</code>
+                        , including a link to download the
+                        <a href="http://java.sun.com/products/javabeans/docs/spec.html">
+                            JavaBeans 1.01 Specification</a>
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/docs/books/tutorial/javabeans/index.html">
+                            <strong>The JavaBeans Trail</strong>
+                        </a>
+                        in the Java Tutorial
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/JSPBeans.html">
+                            <strong>JavaBeans Components in JSP Pages</strong>
+                        </a>
+                        in the Java Web Services Tutorial
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="reflection"/>
+            <subsection name="0.5.1 Reflection and Introspection">
+
+                <p>
+                    Reflection is the process of determining which member
+                    fields and methods are available on an object.
+                    Introspection is a specialized form of reflection used by
+                    the JavaBean API.
+                    Using Introspection, we can determine which methods of a
+                    JavaBean are intended to be accessed by other objects.
+                    (The getters and the setters, for example.)
+                </p>
+
+                <p>
+                    The framework uses Introspection to convert HTTP
+                    parameters into JavaBean properties and to populate HTML
+                    fields from JavaBean properties.
+                    This technique makes it easy to "roundtrip" properties
+                    between HTML forms and JavaBeans.
+                </p>
+
+                <p>
+                    For more about Reflection and Introspection, see
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/docs/books/tutorial/reflect/">
+                            The Reflection Trail</a>
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/products/javabeans/docs/spec.html">
+                            Chapter 8 of the JavaBeans API Specification</a>
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="maps"/>
+            <subsection name="0.5.2 Maps">
+
+                <p>
+                    JavaBeans store data as properties and may act on that
+                    data through other methods.
+                    JavaBeans are flexible and powerful objects but are not
+                    the only object that programmers use to store data.
+                    Another popular object is the Map [
+                    <code>java.util.Map</code>
+                    ].
+                    A Map is a simple collection of name and value pairs.
+                    Maps are often used "behind the scenes" as a flexible way
+                    to store dynamic data.
+                </p>
+
+            </subsection>
+
+            <a name="dynabeans"/>
+            <subsection name="0.5.3 DynaBeans">
+
+                <p>
+                    DynaBeans combine the extensibility of JavaBeans with the
+                    flexibility of a Map.
+                    Defining even the simplest JavaBean requires defining a
+                    new class and coding a field and two methods for each
+                    property.
+                    The properties of a DynaBean can be configured via an XML
+                    descriptor.
+                    The virtual properties of a DynaBean can't be called by
+                    standard Java methods,
+                    but work well with components that rely on reflection and
+                    introspection.
+                </p>
+
+                <p>
+                    In your application, you can use DynaBeans to describe
+                    your HTML forms.
+                    This strategy can avoid creating a formal JavaBean
+                    subclass to store a few simple properties.
+                </p>
+
+                <p>
+                    For more about DynaBeans, see
+                </p>
+
+                <ul>
+                    <li>
+                        The Commons BeanUtils
+                        <a href="http://jakarta.apache.org/commons/beanutils/api/org/apache/commons/beanutils/package-summary.html#package_description">
+                            Package Description</a>
+                        and
+                        <a href="http://jakarta.apache.org/commons/beanutils/api/index.html">
+                            Javadocs</a>
+                        .
+                    </li>
+                    <li>
+                        <a href="https://formdef.dev.java.net/">Struts
+                            FormDef</a>
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="resources"/>
+            <subsection name="0.6 Properties Files and ResourceBundles">
+
+                <p>Java applications, including web applications, are often
+                    configured using
+                    <a href="http://java.sun.com/j2se/1.4.1/docs/api/java/util/Properties.html">
+                        Properties</a>
+                    files. Properties files are the basis for the
+                    <a href="http://java.sun.com/j2se/1.4.1/docs/api/java/util/ResourceBundle.html">
+                        ResourceBundles</a>
+                    that the framework uses to provide message resources
+                    to an application.
+                </p>
+
+                <p>For more about Properties files, see:</p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/docs/books/tutorial/essential/attributes/properties.html">
+                            <strong>Using Properties to Manage Program
+                                Attributes</strong>
+                        </a>
+                        in The Java Tutorial
+                    </li>
+                </ul>
+
+                <p>Java ResourceBundles use one or more Properties files to
+                    provide internationalized messages
+                    to users based their
+                    <a href="http://java.sun.com/j2se/1.4.1/docs/api/java/util/Locale.html">
+                        Locale</a>
+                    .
+                    Support for localizing an application was built into the
+                    framework from the ground-up.
+                </p>
+
+                <p>For more about localization and ResourceBundles, see</p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/docs/books/tutorial/i18n/resbundle/concept.html">
+                            <strong>About the ResourceBundle Class</strong>
+                        </a>
+                        in the Java Tutorial
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="servlets"/>
+            <subsection name="0.7 Java Servlets">
+                <p>
+                    Since Java is an object-orientated language, the
+                    <a href="http://www.novocode.com/doc/servlet-essentials/">
+                        Java Servlet</a>
+                    platform strives to cast HTTP into an object-orientated
+                    form.
+                    This strategy makes it easier for Java developers to
+                    concentrate on what they need their application to do --
+                    rather than the mechanics of HTTP.
+                </p>
+
+                <p>
+                    HTTP provides a standard mechanism for extending servers
+                    called the Common Gateway Interface, or CGI.
+                    The server can pass a request to a CGI-aware program, and
+                    the program will pass back a response.
+                    Likewise, a Java-aware server can pass a request to a
+                    servlet container.
+                    The container can fulfill the request or it can pass the
+                    request back to the HTTP server.
+                    The container decides whether it can handle the request by
+                    checking its list of servlets.
+                    If there is a servlet registered for the request, the
+                    container passes the request to the servlet.
+                </p>
+
+                <p>
+                    When a request comes in, the container checks to see if
+                    there is a servlet registered for that request.
+                    If there is a match,
+                    the request is given to the servlet.
+                    If not, the request is returned to the HTTP server.
+                </p>
+
+                <p>
+                    It's the container's job to manages the servlet lifecycle.
+                    The container creates the servlets, invokes the servlets,
+                    and ultimately disposes the servlets.
+                </p>
+
+                <p>
+                    A servlet is generally a subclass of
+                    <code>javax.servlet.http.HttpServlet</code>
+                    .
+                    A servlet must implement four methods, which are invoked
+                    by the container as needed:
+                </p>
+
+                <ul>
+                    <li>
+                        <strong>public void init(ServletConfig
+                            config)</strong>
+                        - Called by the
+                        servlet container when the servlet instance is first
+                        created, and
+                        before any request is processed.
+                    </li>
+                    <li>
+                        <strong>public void doGet(HttpServletRequest request,
+                            HttpServletResponse response)</strong>
+                        - Called to process a
+                        specific request received using the HTTP
+                        <code>GET</code>
+                        protocol,
+                        which generates a corresponding dynamic response.
+                    </li>
+                    <li>
+                        <strong>public void doPost(HttpServletRequest request,
+                            HttpServletResponse response)</strong>
+                        - Called to process a
+                        specific request received using the HTTP
+                        <code>POST</code>
+                        protocol,
+                        which generates a corresponding dynamic response.
+                    </li>
+                    <li>
+                        <strong>public void destroy()</strong>
+                        - Called by the servlet
+                        container when it takes this servlet instance out of
+                        service,
+                        such as when a web application is being undeployed or
+                        when the
+                        entire container is being shut down.
+                    </li>
+                </ul>
+
+                <p>
+                    The framework provides a ready-to-use servlet for your
+                    application [
+                    <code>org.apache.struts.action.ActionServlet</code>
+                    ].
+                    As a Struts developer, you can then just write objects
+                    that the Struts ActionServlet calls when needed.
+                    But it is still helpful to understand the basics of what
+                    servlets are,
+                    and the role they play in a Java web application.
+                </p>
+
+                <p>
+                    For more about Java Servlets, see:
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/products/servlet/">
+                            <strong>The
+                                Java Servlet Technology</strong>
+                        </a>
+                        page at
+                        <code>java.sun.com</code>
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/products/servlet/download.html">
+                            <strong>The
+                                Servlet 2.2 and 2.3 Specifications</strong>
+                        </a>
+                        download page at
+                        <code>java.sun.com</code>
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets.html">
+                            <strong>Java Servlet Technology</strong>
+                        </a>
+                        in the Java Web Services Tutorial.
+                    </li>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/WebApp.html">
+                            <strong>Web Applications</strong>
+                        </a>
+                        in the Java Web Services Tutorial.
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="threads"/>
+            <subsection name="0.7.1 Servlets and threads">
+
+                <p>
+                    To boost performance, the container can multi-thread
+                    servlets.
+                    Only one instance of a particular servlet is created,
+                    and each request for that servlet passes through the same
+                    object.
+                    This strategy helps the container make the best use of
+                    available resources.
+                    The tradeoff is that the servlet's
+                    <code>doGet()</code>
+                    and
+                    <code>doPost()</code>
+                    methods must be programmed in a
+                    <em>thread-safe</em>
+                    manner.
+                </p>
+
+                <p>
+                    For more about servlets and thread-safety, see:
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets5.html#64386">
+                            Controlling Concurrent Access to Shared
+                            Resources</a>
+                        in Java Web Services Tutorial.
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="context"/>
+            <subsection name="0.7.2 Servlet Context">
+
+                <p>The
+                    <em>ServletContext</em>
+                    interface [
+                    <code>javax.servlet.ServletContext</code>
+                    ] defines a servlet's view of
+                    the web application within which the servlet is running.
+                    It is
+                    accessible in a servlet via the
+                    <code>getServletConfig()</code>
+                    method,
+                    and in a JSP page as the
+                    <code>application</code>
+                    implicit variable.
+                    Servlet contexts provide several APIs that are very useful
+                    in building
+                    Struts based web applications:
+                </p>
+                <ul>
+                    <li>
+                        <em>Access To Web Application Resources</em>
+                        - A servlet can
+                        access static resource files within the web
+                        application using the
+                        <code>getResource()</code>
+                        and
+                        <code>getResourceAsStream()</code>
+                        methods.
+                    </li>
+                    <li>
+                        <em>Servlet Context Attributes</em>
+                        - The context makes available
+                        a storage place for Java objects, identified by
+                        string-valued keys.
+                        These attributes are global to the entire web
+                        application, and may
+                        be accessed by a servlet using the
+                        <code>getAttribute()</code>
+                        ,
+                        <code>getAttributeNames()</code>
+                        ,
+                        <code>removeAttribute()</code>
+                        , and
+                        <code>setAttribute()</code>
+                        methods. From a JSP page, servlet
+                        context attributes are also known as "application
+                        scope beans".
+                    </li>
+                </ul>
+
+                <p>
+                    For more about the servlet context, see:
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets10.html#64724">
+                            Accessing the Web Context</a>
+                        in Java Web Services Tutorial.
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="request"/>
+            <subsection name="0.7.3 Servlet Request">
+
+                <p>Each request processed by a servlet is represented by a
+                    Java
+                    interface, normally a
+                    <code>HttpServletRequest</code>
+                    [
+                    <code>javax.servlet.http.HttpServletRequest</code>
+                    ].
+                    The request interface provides an object-oriented
+                    mechanism to access
+                    all of the information that was included in the underlying
+                    HTTP request,
+                    including:
+                </p>
+                <ul>
+                    <li>
+                        <em>Cookies</em>
+                        - The set of cookies included with this request
+                        are available via the
+                        <code>getCookies()</code>
+                        method.
+                    </li>
+                    <li>
+                        <em>Headers</em>
+                        - HTTP headers that were included with
+                        the request are accessible by name. You can enumerate
+                        the names
+                        of all included headers.
+                    </li>
+                    <li>
+                        <em>Parameters</em>
+                        - Request parameters, including those from
+                        the query string portion of the URL and from the
+                        embedded content
+                        of the request (POST only) are available by name.
+                    </li>
+                    <li>
+                        <em>Request Characteristics</em>
+                        - Many other characteristics
+                        of the incoming HTTP request, such as the method used
+                        (normally
+                        GET or POST) the protocol scheme used ("http" or
+                        "https"), and
+                        similar values.
+                    </li>
+                    <li>
+                        <em>Request URI Information</em>
+                        - The original request URI
+                        being processed is available via
+                        <code>getRequestURI()</code>
+                        .
+                        In addition, the constituent parts into which the
+                        servlet container
+                        parses the request URI (contextPath, servletPath, and
+                        pathInfo) are
+                        available separately.
+                    </li>
+                    <li>
+                        <em>User Information</em>
+                        - If you are using
+                        <a href="#security">Container Managed Security</a>
+                        , you can ask for
+                        the username of the authenticated user, retrieve a
+                        <code>Principal</code>
+                        object representing the current user, and
+                        whether the current user is authorized for a specified
+                        role.
+                    </li>
+                </ul>
+
+                <p>In addition, servlet requests support
+                    <em>request attributes</em>
+                    (from JSP, these are "request scope beans"), analogous to
+                    the servlet
+                    context attributes described above. Request attributes are
+                    often used
+                    to communicate state information from a business logic
+                    class that
+                    generates it to a view component (such as a JSP page) that
+                    will use
+                    the information to produce the corresponding response.
+                </p>
+
+                <p>The servlet container guarantees that a particular request
+                    will
+                    be processed by a servlet on a single thread. Therefore,
+                    you do not
+                    generally have to worry about the thread safety of your
+                    access to
+                    request properties and attributes.</p>
+
+                <p>
+                    For more about the servlet request, see:
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets7.html#64433">
+                            Getting Information from Requests</a>
+                        in Java Web Services Tutorial.
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="response"/>
+            <subsection name="0.7.4 Servlet Response">
+
+                <p>The primary purpose of a servlet is to process an incoming
+                    <a href="#request">Servlet Request</a>
+                    [
+                    <code>javax.servlet.http.HttpServletRequest</code>
+                    ]
+                    and convert it into a
+                    corresponding response. This is performed by calling
+                    appropriate
+                    methods on the servlet response [
+                    <code>javax.servlet.http.HttpServletResponse</code>
+                    ]
+                    interface. Available methods let you:
+                </p>
+                <ul>
+                    <li>
+                        <em>Set Headers</em>
+                        - You can set HTTP headers that will be
+                        included in the response. The most important header is
+                        the
+                        <code>Content-Type</code>
+                        header, which tells your client what
+                        kind of information is included in the body of this
+                        response.
+                        This is typically set to
+                        <code>text/html</code>
+                        for an HTML page,
+                        or
+                        <code>text/xml</code>
+                        for an XML document.
+                    </li>
+                    <li>
+                        <em>Set Cookies</em>
+                        - You can add cookies to the current
+                        response.
+                    </li>
+                    <li>
+                        <em>Send Error Responses</em>
+                        - You can send an HTTP error status
+                        (instead of a usual page of content) using
+                        <code>sendError()</code>
+                        .
+                    </li>
+                    <li>
+                        <em>Redirect To Another Resource</em>
+                        - You can use the
+                        <code>sendRedirect()</code>
+                        method to redirect the client to
+                        some other URL that you specify.
+                    </li>
+                </ul>
+
+                <p>An important principle in using the servlet response APIs
+                    is that
+                    any methods you call to manipulate headers or cookies
+                    <strong>MUST</strong>
+                    be performed before the first buffer-full of
+                    content has been flushed to the client. The reason for
+                    this restriction
+                    is that such information is transmitted at the beginning
+                    of the HTTP
+                    response, so trying things like adding a header after the
+                    headers have
+                    already been sent will not be effective.
+                </p>
+
+                <p>
+                    When you are using presentation pages in a Model 2
+                    application,
+                    you will not generally use the servlet response APIs
+                    directly.
+                    In the case of JavaServerPages, the JSP page compiler
+                    in your servlet container will convert your page into a
+                    servlet.
+                    The JSP servlet renders the response, interspersing
+                    dynamic
+                    information where you have interposed JSP custom tags.
+                </p>
+
+                <p>
+                    Other presentation systems, like Velocity Tools for
+                    Struts,
+                    may delegate rendering the response to a specialized
+                    servlet,
+                    but the same pattern holds true.
+                    You create a template,
+                    and the dynamic response is generated automatically from
+                    the template.
+                </p>
+
+                <p>
+                    For more about the servlet response, see:
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets7.html#64531">
+                            Constructing Responses</a>
+                        in Java Web Services Tutorial.
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="filter"/>
+            <subsection name="0.7.5 Filtering">
+
+                <p>If you are using a servlet container based on version
+                    <strong>2.3</strong>
+                    or later of the Servlet Specification (such as
+                    Tomcat 4.x), you can take advantage of the new Filter APIs
+                    [
+                    <code>javax.servlet.Filter</code>
+                    ] that
+                    let you compose a set of components that will process a
+                    request or
+                    response. Filters are aggregated into a chain in which
+                    each filter
+                    has a chance to process the request and response before
+                    and after
+                    it is processed by subsequent filters (and the servlet
+                    that is ultimately
+                    called).
+                </p>
+
+                <p>The Struts 1.0, 1.1, and 1.2 versions require only version
+                    2.2 or later
+                    of the Servlet Specification to be implemented by your
+                    servlet container,
+                    so those versions do not use Filters. Beginning with the
+                    1.3 version, a container that supports version 2.3 or
+                    later of the Servlet
+                    Specification is required, and it is possible that the
+                    framework might use
+                    Filters in the future.</p>
+
+                <p>
+                    For more about filters, see:
+                </p>
+
+                <ul>
+                    <li>
+                        <a href="http://java.sun.com/webservices/docs/1.0/tutorial/doc/Servlets8.html#64572">
+                            Filtering Requests and Responses</a>
+                    </li>
+                </ul>
+
+            </subsection>
+
+            <a name="session"/>
+            <subsection name="0.7.6 Sessions">
+
+                <p>One of the key characteristics of HTTP is that it is
+                    <em>stateless</em>
+                    . In other words, there is nothing built in to
+                    HTTP that identifies a subsequent request from the same
+                    user as being
+                    related to a previous request from that user. This makes
+                    building an
+                    application that wants to engage in a conversation with
+                    the user over
+                    several requests to be somewhat difficult.
+                </p>
+

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