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From hus...@apache.org
Subject cvs commit: jakarta-commons-sandbox/chain/src/java/org/apache/commons/chain/web ChainListener2.java
Date Wed, 01 Oct 2003 17:04:02 GMT
husted      2003/10/01 10:04:02

  Added:       chain/src/java/org/apache/commons/chain/web
                        ChainListener2.java
  Log:
  ContextListener that loads resoruces from classpath on demand.
  
  Revision  Changes    Path
  1.1                  jakarta-commons-sandbox/chain/src/java/org/apache/commons/chain/web/ChainListener2.java
  
  Index: ChainListener2.java
  ===================================================================
  /*
   * $Header: /home/cvs/jakarta-commons-sandbox/chain/src/java/org/apache/commons/chain/web/ChainListener2.java,v
1.1 2003/10/01 17:04:02 husted Exp $
   * $Revision: 1.1 $
   * $Date: 2003/10/01 17:04:02 $
   *
   * ====================================================================
   *
   * The Apache Software License, Version 1.1
   *
   * Copyright (c) 1999-2003 The Apache Software Foundation.  All rights
   * reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. The end-user documentation included with the redistribution, if
   *    any, must include the following acknowlegement:
   *       "This product includes software developed by the
   *        Apache Software Foundation (http://www.apache.org/)."
   *    Alternately, this acknowlegement may appear in the software itself,
   *    if and wherever such third-party acknowlegements normally appear.
   *
   * 4. The names "The Jakarta Project", "Commons", and "Apache Software
   *    Foundation" must not be used to endorse or promote products derived
   *    from this software without prior written permission. For written
   *    permission, please contact apache@apache.org.
   *
   * 5. Products derived from this software may not be called "Apache"
   *    nor may "Apache" appear in their names without prior written
   *    permission of the Apache Group.
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  
  
  package org.apache.commons.chain.web;
  
  
  import org.apache.commons.chain.Catalog;
  import org.apache.commons.chain.config.ConfigParser;
  import org.apache.commons.chain.impl.CatalogBase;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import javax.servlet.ServletContext;
  import javax.servlet.ServletContextEvent;
  import javax.servlet.ServletContextListener;
  import java.net.URL;
  
  
  /**
   * EXPERIMENTAL CLASS :: MAY BE REMOVED AT ANY TIME.
   *
   * <p>Optional <code>ServletContextListener</code> that automatically
   * scans chain configuration files in the current web application at
   * startup time, and exposes the result in a {@link Catalog} under a
   * specified servlet context attribute.  The following
   * <code>context-param</code> attributes are utilized:</p>
   * <ul>
   * <li><strong>org.apache.commons.chain.CONFIG_WEB_RESOURCE</strong> -
   *     comma-delimited list of chain configuration webapp resources
   *     to be loaded.  (For example,
   *     <code>/WEB-INF/chain-config.xml</code>.)</li>
   * <li><strong>org.apache.commons.chain.CONFIG_RESOURCE</strong> -
   *     comma-delimited list of chain configuration classpath resources
   *     to be loaded.  (For example,
   *     <code>com/myCompany/command/ChainConfig.xml</code>.)</li>
   * <li><strong>org.apache.commons.chain.CONFIG_CATALOG</strong> -
   *     Name of the servlet context attribute under which the
   *     resulting {@link Catalog} will be exposed.  If not specified,
   *     defaults to <code>Chain.CATALOG_KEY</code>.</li>
   * </ul>
   *
   * <p>When a web application that has configured this listener is
   * started, it will create a new {@link Catalog} (if needed) and populate it by
   * scanning configuration resources from the init parameter described
   * above.  If a {@link Catalog} instance already exists at the specified
   * attribute, any new parsed definitions will be merged into the existing
   * catalog (the last definition for a particular name wins). </p>
   *
   * <p>At least one configuration file must be specified, using either
   * the <code>org.apache.commons.chain.CONFIG_WEB_RESOURCE</code> or
   * <code>org.apache.commons.chain.CONFIG_RESOURCE<code> context attributes,
   * or a runtime error occurs. You may also specify more than one file, using
   * either or both attributes.</p>
   *
   * <p>This class requires Servlet 2.3 or later.  If you are running on
   * a Servlet 2.2 system, consider using {@link ChainServlet} instead.</p>
   *
   * <p>To configure the listener, add an elements like this to the web deployment descriptor
(web.xml),
   * before any servlet elements: </p>
   *
   * <pre><code>
   * &lt;context-param>
   *        &lt;param-name>org.apache.commons.chain.CONFIG_RESOURCE&lt;/param-name>
   *        &lt;param-value>us_ok_deq_wqdata/command/ChainConfig.xml&lt;/param-value>
   * &lt;/context-param>
   *
   * &lt;context-param>
   *        &lt;param-name>org.apache.commons.chain.CONFIG_WEB_RESOURCE&lt;/param-name>
   *        &lt;param-value>/WEB-INF/chain-config.xml&lt;/param-value>
   * &lt;/context-param>
   *
   * &lt;listener>
   *    &lt;listener-class>org.apache.commons.chain.web.ChainListener2&lt;/listener-class>
   * &lt;/listener>
   * </code></pre>
   *
   * @author Craig R. McClanahan
   * @author Ted Husted
   * @version $Revision: 1.1 $ $Date: 2003/10/01 17:04:02 $
   */
  
  public class ChainListener2 implements ServletContextListener {
  
  
      // ------------------------------------------------------ Manifest Constants
  
  
      /**
       * <p>The default servlet context attribute key.</p>
       */
      private static final String CONFIG_ATTR_DEFAULT = Catalog.CATALOG_KEY;
  
  
      /**
       * <p>The name of the context init parameter containing the name of the
       * servlet context attribute under which our resulting {@link Catalog}
       * will be stored.</p>
       */
      public static final String CONFIG_ATTR =
              "org.apache.commons.chain.CONFIG_ATTR";
  
  
      /**
       * <p>The name of the context init parameter containing a comma-delimited
       * list of web applicaton resources to be scanned.</p>
       */
      public static final String CONFIG_WEB_RESOURCE =
              "org.apache.commons.chain.CONFIG_WEB_RESOURCE";
  
      /**
       * <p>The name of the context init parameter containing a comma-delimited
       * list of resources on the application classpath to be scanned.</p>
       */
      public static final String CONFIG_RESOURCE =
              "org.apache.commons.chain.CONFIG_RESOURCE";
  
      // -------------------------------------------------------- Static Variables
  
  
      /**
       * <p>The <code>Log</code> instance for this class.</p>
       */
      private static final Log log = LogFactory.getLog(ChainListener2.class);
  
  
      // ------------------------------------------ ServletContextListener Methods
  
  
      /**
       * <p>Remove the configured {@link Catalog} from the servlet context
       * attributes for this web application.</p>
       *
       * @param event <code>ServletContextEvent</code> to be processed
       */
      public void contextDestroyed(ServletContextEvent event) {
  
          ServletContext context = event.getServletContext();
          String attr = context.getInitParameter(CONFIG_ATTR);
          if (attr == null) {
              attr = CONFIG_ATTR_DEFAULT;
          }
          context.removeAttribute(attr);
  
      }
  
  
      /**
       * Add Chains and/or Commands from one or more web resource
       * configuration files to the runtime Catalog.
       *
       * @param resource A comma-delimited list of web resources
       * @param context ServletContext instance to locate web resources
       * @param parser ConfigParser instance to parse the configuration file
       * @param catalog Catalog instance to which Commands and Chains are added
       */
      private void parseWebResource(String resource, ServletContext context, ConfigParser
parser, Catalog catalog) {
          String path = null;
          try {
              while (true) {
                  int comma = resource.indexOf(",");
                  if (comma < 0) {
                      path = resource.trim();
                      resource = "";
                  } else {
                      path = resource.substring(0, comma);
                      resource = resource.substring(comma + 1);
                  }
                  if (path.length() < 1) {
                      break;
                  }
                  URL url = context.getResource(path);
                  if (url == null) {
                      throw new IllegalStateException
                              ("Missing chain config resource '" + path + "'");
                  }
                  if (log.isDebugEnabled()) {
                      log.debug("Loading chain config resource '" + path + "'");
                  }
                  parser.parse(catalog, url);
              }
          } catch (Exception e) {
              throw new RuntimeException
                      ("Exception parsing chain config resource '" + path + "': " +
                      e.getMessage());
          }
      }
  
  
      /**
       * Add Chains and/or Commands from one or more classpath resource
       * configuration files to the runtime Catalog.
       *
       * @param resource A comma-delimited list of web resources
       * @param parser ConfigParser instance to parse the configuration file
       * @param catalog Catalog instance to which Commands and Chains are added
       */
      private void parseResource(String resource, ConfigParser parser, Catalog catalog) {
          String path = null;
          URL configResource = null;
          try {
              while (true) {
                  int comma = resource.indexOf(",");
                  if (comma < 0) {
                      path = resource.trim();
                      resource = "";
                  } else {
                      path = resource.substring(0, comma);
                      resource = resource.substring(comma + 1);
                  }
                  if (path.length() < 1) {
                      break;
                  }
  
                  log.info("Loading classloader resources from '" +
                          resource + "'");
  
                  ClassLoader loader =
                          Thread.currentThread().getContextClassLoader();
                  if (loader == null) {
                      loader = this.getClass().getClassLoader();
                  }
                  configResource = loader.getResource(path);
  
                  parser.parse(catalog, configResource);
  
              }
          } catch (Exception e) {
              throw new RuntimeException
                      ("Exception parsing chain config resource '" + path + "': " +
                      e.getMessage());
          }
      }
  
  
      /**
       * <p>Scan the required chain configuration resources, assemble the
       * configured chains into a {@link Catalog}, and expose it as a
       * servlet context attribute under the specified key.</p>
       *
       * @param event <code>ServletContextEvent</code> to be processed
       */
      public void contextInitialized(ServletContextEvent event) {
  
          ServletContext context = event.getServletContext();
          String attr = context.getInitParameter(CONFIG_ATTR);
          if (attr == null) {
              attr = CONFIG_ATTR_DEFAULT;
          }
  
          // Retrieve or create the Catalog instance we will be updating
          Catalog catalog = (Catalog) context.getAttribute(attr);
          if (catalog == null) {
              catalog = new CatalogBase();
          }
  
          // Construct the configuration resource parser we will use
          // FIXME - Do we need to make this more configurable?
          ConfigParser parser = new ConfigParser();
  
          // Parse the web resources specified in our init parameter (if any)
          String webResource = context.getInitParameter(CONFIG_WEB_RESOURCE);
          if (webResource != null) parseWebResource(webResource, context, parser, catalog);
  
          // Parse the class resources specified in our init parameter (if any)
          String resource = context.getInitParameter(CONFIG_RESOURCE);
          if (resource != null) parseResource(resource, parser, catalog);
  
          if ((webResource == null) && (resource == null)) {
              throw new RuntimeException
                      ("ChainListener2: At least one resource must be specified '");
          }
  
          // Expose the completed catalog
          context.setAttribute(attr, catalog);
  
      }
  
  }
  
  
  

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