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Classloading and caching changes
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reply from <a href="http://community.jboss.org/people/alesj">Ales Justin</a> in <i>JBoss Microcontainer Development</i> - <a href="http://community.jboss.org/message/543114#543114">View the full discussion</a>
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<div class="jive-rendered-content"><p>So, once we determined what we need to do, this is how it's impled atm.</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>A new CachedLoader interface was introduced</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code jive-java"><font color="navy"><b>public</b></font> <font color="navy"><b>interface</b></font> CacheLoader <font color="navy"><b>extends</b></font> Loader
<font color="navy">{</font>
   <font color="darkgreen">/**
    * Check the class cache.
    *
    * @param classLoader the reference classloader (possibly null)
    * @param name the name of the class
    * @param path the path of the class resource
    * @param allExports whether to look at all exports
    * @return the class if cached
    */</font>
   Class<?> checkClassCache(BaseClassLoader classLoader, String name, String path, <font color="navy"><b>boolean</b></font> allExports);
<font color="navy">}</font>
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>where the BaseClassLoaderDomain does before and after checks</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code jive-java">   <font color="navy"><b>public</b></font> Class<?> checkClassCache(BaseClassLoader classLoader, String name, String path, <font color="navy"><b>boolean</b></font> allExports)
   <font color="navy">{</font>
      Class<?> result = checkCacheBefore(classLoader, name, path, allExports);
      <font color="navy"><b>if</b></font> (result != <font color="navy"><b>null</b></font>)
         <font color="navy"><b>return</b></font> result;
 
      result = checkCacheAfter(classLoader, name, path, allExports);
      <font color="navy"><b>if</b></font> (result != <font color="navy"><b>null</b></font>)
         <font color="navy"><b>return</b></font> result;
 
      result = checkClassCacheLocally(classLoader, name, path, allExports);
      <font color="navy"><b>if</b></font> (result != <font color="navy"><b>null</b></font>)
         <font color="navy"><b>return</b></font> result;
 
      <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
   <font color="navy">}</font>
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>where the actual impl lives in ClassLoaderDomain</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code jive-java"><font color="navy"><b>protected</b></font> Class<?> checkCacheBefore(BaseClassLoader classLoader, String name, String path, <font color="navy"><b>boolean</b></font> allExports)
   <font color="navy">{</font>
      <font color="navy"><b>if</b></font> (parent == <font color="navy"><b>null</b></font> || parent <font color="navy"><b>instanceof</b></font> CacheLoader == <font color="navy"><b>false</b></font>)
         <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
 
      ClassFilter filter = getParentPolicy().getBeforeFilter();
      <font color="navy"><b>if</b></font> (filter.matchesClassName(name))
      <font color="navy">{</font>
         CacheLoader loader = (CacheLoader) parent;
         <font color="navy"><b>return</b></font> loader.checkClassCache(classLoader, name, path, allExports);
      <font color="navy">}</font>
      <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
   <font color="navy">}</font>
 
   <font color="darkgreen">/**
    * Only check parent after if we already blacklisted this resource.
    */</font>
   @Override
   <font color="navy"><b>protected</b></font> Class<?> checkCacheAfter(BaseClassLoader classLoader, String name, String path, <font color="navy"><b>boolean</b></font> allExports)
   <font color="navy">{</font>
      <font color="navy"><b>if</b></font> (parent == <font color="navy"><b>null</b></font> || parent <font color="navy"><b>instanceof</b></font> CacheLoader == <font color="navy"><b>false</b></font> || isBlackListedClass(path) == <font color="navy"><b>false</b></font>)
         <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
 
      ClassFilter filter = getParentPolicy().getAfterFilter();
      <font color="navy"><b>if</b></font> (filter.matchesClassName(name))
      <font color="navy">{</font>
         CacheLoader loader = (CacheLoader) parent;
         <font color="navy"><b>return</b></font> loader.checkClassCache(classLoader, name, path, allExports);
      <font color="navy">}</font>
      <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
   <font color="navy">}</font>
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>The 3 current CacheLoader impls are</p><p>* BaseClassLoaderDomain (we already saw its impl)</p><p>* BaseDelegateLoader (it just delegates to its domain)</p><p>* ClassLoaderToLoaderAdapter (see below)</p><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><pre class="jive-pre"><code class="jive-code jive-java">  <font color="navy"><b>public</b></font> Class<?> checkClassCache(BaseClassLoader bcl, String name, String path, <font color="navy"><b>boolean</b></font> allExports)
   <font color="navy">{</font>
      <font color="navy"><b>if</b></font> (findLoadedClass == <font color="navy"><b>null</b></font>)
         <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
 
      <font color="navy"><b>final</b></font> ClassLoader classLoader = getClassLoader();
      <font color="navy"><b>try</b></font>
      <font color="navy">{</font>
         <font color="navy"><b>return</b></font> (Class<?>) findLoadedClass.invoke(classLoader, name);
      <font color="navy">}</font>
      <font color="navy"><b>catch</b></font> (Exception e)
      <font color="navy">{</font>
         log.warn(<font color="red">"Unexpected error retrieving found class "</font> + name + <font color="red">" from classloader "</font> + classLoader, e);
         <font color="navy"><b>return</b></font> <font color="navy"><b>null</b></font>;
      <font color="navy">}</font>
   <font color="navy">}</font>
</code></pre><p style="min-height: 8pt; height: 8pt; padding: 0px;"> </p><p>I have also hacked a simple debug-able mock in Deployers project -- where we can check different deployment types</p><p><span>* </span><a class="jive-link-external-small" href="http://anonsvn.jboss.org/repos/jbossas/projects/jboss-deployers/trunk/deployers-vfs/src/test/java/org/jboss/test/deployers/vfs/classloading/test/ClassLoaderCachingTestCase.java" target="_blank">http://anonsvn.jboss.org/repos/jbossas/projects/jboss-deployers/trunk/deployers-vfs/src/test/java/org/jboss/test/deployers/vfs/classloading/test/ClassLoaderCachingTestCase.java</a></p></div>
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<p style="margin: 0;">Start a new discussion in JBoss Microcontainer Development at <a href="http://community.jboss.org/choose-container!input.jspa?contentType=1&containerType=14&container=2115">Community</a></p>
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