start implementation of isolated classloaders

scm-webapp/src/main/java/sonia/scm/plugin/UberClassLoader.java

@@ -0,0 +1,202 @@
+/**
+ * Copyright (c) 2010, Sebastian Sdorra 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. Neither the name of SCM-Manager;
+ * nor the names of its contributors may be used to endorse or promote products
+ * derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS 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 REGENTS OR 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.
+ *
+ * http://bitbucket.org/sdorra/scm-manager
+ *
+ */
+
+
+
+package sonia.scm.plugin;
+
+//~--- non-JDK imports --------------------------------------------------------
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+
+//~--- JDK imports ------------------------------------------------------------
+
+import java.io.IOException;
+
+import java.lang.ref.WeakReference;
+
+import java.net.URL;
+
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.concurrent.ConcurrentMap;
+
+/**
+ * {@link ClassLoader} which is able to load classes and resources from all
+ * plugins.
+ *
+ * @author Sebastian Sdorra
+ */
+public final class UberClassLoader extends ClassLoader
+{
+
+  /**
+   * Constructs ...
+   *
+   *
+   * @param parent
+   * @param plugins
+   */
+  public UberClassLoader(ClassLoader parent, Iterable<PluginWrapper> plugins)
+  {
+    super(parent);
+    this.plugins = plugins;
+  }
+
+  //~--- methods --------------------------------------------------------------
+
+  /**
+   * Method description
+   *
+   *
+   * @param name
+   *
+   * @return
+   *
+   * @throws ClassNotFoundException
+   */
+  @Override
+  protected Class<?> findClass(String name) throws ClassNotFoundException
+  {
+    Class<?> clazz = getFromCache(name);
+
+    if (clazz == null)
+    {
+      for (PluginWrapper plugin : plugins)
+      {
+        ClassLoader cl = plugin.getClassLoader();
+
+        // load class could be slow, perhaps we should call
+        // find class via reflection ???
+        clazz = cl.loadClass(name);
+
+        if (clazz != null)
+        {
+          cache.put(name, new WeakReference<Class<?>>(clazz));
+
+          break;
+        }
+      }
+    }
+
+    return clazz;
+  }
+
+  /**
+   * Method description
+   *
+   *
+   * @param name
+   *
+   * @return
+   */
+  @Override
+  protected URL findResource(String name)
+  {
+    URL url = null;
+
+    for (PluginWrapper plugin : plugins)
+    {
+      ClassLoader cl = plugin.getClassLoader();
+
+      url = cl.getResource(name);
+
+      if (url != null)
+      {
+        break;
+      }
+    }
+
+    return url;
+  }
+
+  /**
+   * Method description
+   *
+   *
+   * @param name
+   *
+   * @return
+   *
+   * @throws IOException
+   */
+  @Override
+  protected Enumeration<URL> findResources(String name) throws IOException
+  {
+    List<URL> urls = Lists.newArrayList();
+
+    for (PluginWrapper plugin : plugins)
+    {
+      ClassLoader cl = plugin.getClassLoader();
+
+      urls.addAll(Collections.list(cl.getResources(name)));
+    }
+
+    return Collections.enumeration(urls);
+  }
+
+  //~--- get methods ----------------------------------------------------------
+
+  /**
+   * Method description
+   *
+   *
+   * @param name
+   *
+   * @return
+   */
+  private Class<?> getFromCache(String name)
+  {
+    Class<?> clazz = null;
+    WeakReference<Class<?>> ref = cache.get(name);
+
+    if (ref != null)
+    {
+      clazz = ref.get();
+
+      if (clazz == null)
+      {
+        cache.remove(name);
+      }
+    }
+
+    return clazz;
+  }
+
+  //~--- fields ---------------------------------------------------------------
+
+  /** Field description */
+  private final ConcurrentMap<String, WeakReference<Class<?>>> cache =
+    Maps.newConcurrentMap();
+
+  /** Field description */
+  private final Iterable<PluginWrapper> plugins;
+}