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From blorit...@apache.org
Subject cvs commit: avalon-excalibur/fortress/src/java/org/apache/avalon/fortress/impl/factory package.html
Date Thu, 24 Apr 2003 20:15:17 GMT
bloritsch    2003/04/24 13:15:17

  Added:       fortress/src/java/org/apache/avalon/fortress/impl/factory
  add documentation
  Revision  Changes    Path
  1.1                  avalon-excalibur/fortress/src/java/org/apache/avalon/fortress/impl/factory/package.html
  Index: package.html
    ObjectFactory wrappers to provide proxied components to the container.
  <h1>Proxy Factories</h1>
    There are currently two types of factories available with Fortress: BCEL
    enabled, and traditional JDK 1.3 proxies.
    <a href="http://jakarta.apache.org/bcel/">Jakarta BCEL</a> is a library to
    directly generate Java class bytecode.  You do not have to include this
    library for Fortress to function, however if it is present Fortress will
    use it.
  <h2>The Need</h3>
    Proxies are used both for the protection of the component's lifecycle methods,
    and for backwards compatibility with Composable components.  The proxy
    automatically adds the <code>Component</code> interface to any component (even
    if it did not have it in the source code) so that it can be used with your
    old legacy components.  As everyone upgrades, the backwards compatibility
    concern becomes less of an issue--however protecting a component is still
    very important.
  <h2>JDK 1.3 Proxy Code</h2>
    The Java Proxy code uses reflection to do its dirty work, so despite all the
    advances in JDK 1.4 introspection code you will still incur a substantial
    performance bottleneck using this approach.  A user did a micro-benchmark
    and reported that the performance hit is around 4:1 vs. just using the component
    directly.  If your components are not repeatedly called several times in rapid
    succession as is the case with micro-benchmarks then you probably will barely
    notice the change.  Nevertheless, in some environments (most notably when you
    are working with Servlets) that performance hit will begin to add up.
  <h2>BCEL Enabled Proxy Code</h2>
    The BCEL enabled proxy code creates a wrapper class that directly calls the
    methods on your component as if you wrote it yourself.  As an example, the
    following two code snippets will show you how the component is proxied:
  <h3>Component's Interface</h3>
  public interface HelloWorldComponent
      String sayHello();
  <h3>Wrapper Class</h3>
  public final class HelloWorldComponent$BCELWrapper
      private final HelloWorldComponent m_component;
      public HelloWorldComponent$BCELWrapper(HelloWorldComponent base)
          m_component = base;
      public String sayHello()
          return m_component.sayHello();
  <h3>The Benefit</h3>
    The resulting code is much easier for the JVM to use, and does not pose a
    serious threat to the performance of the component.  All you have to do is
    include the BCEL.jar file, and the choice will be made for you.

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