Changeset 7192

Timestamp:

Aug 29, 2016, 2:47:49 PM (7 years ago)

Author:

Nicklas Nordborg

Message:

References #2027: Improve inter-communication between extensions

The original idea that X-Extension-Class-Path should specify extensions that are needed did not work. The extension system may load code (eg. ActionFactory and Action instances; see Three.java in this change) during the initialization of the extension system. The extensions are not registered until everything has been properly setup. If one extension then need to use another extension it will not be able to find it since it has not yet been registered.

The new approach is to simply only use the Class-Path attribute in the MANIFEST.MF file. If the referenced JAR file already exists it is no longer loaded immediately. Instead a proxy instance is created which will create the real class loader when needed. JAR files that are packages inside the META-INF/lib directory are not affected by this change. The code is still loaded before the extension system has been setup but since we now have the filename we do not have to ask the extension system to translate. The drawback is that extensions must be installed with the original filename.

This change also breaks the findResource() and hasChanged() methods which no longer searches the proxied JAR files.

Location:

trunk

Files:

• build.xml (modified) (1 diff)
• src/core/net/sf/basedb/util/JarClassLoader.java (modified) (10 diffs)
• src/test/net/sf/basedb/test/extension/jar3/Three.java (modified) (2 diffs)

trunk/build.xml

@@ -709 +709 @@
       <metainf file="${test.src}/net/sf/basedb/test/extension/jar3/extensions.xml" />
       <manifest>
-        <attribute name="X-Extension-Class-Path" value="extension-in-jar1 extension-in-jar2" />
+        <attribute name="Class-Path" value="ExtensionOne.jar ExtensionTwo.jar" />
       </manifest>
     </jar>

trunk/src/core/net/sf/basedb/util/JarClassLoader.java

@@ -28 +28 @@
 import java.util.Map;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.Enumeration;
 import java.util.Vector;
@@ -135 +136 @@
   }
   
-  
   /**
     Get a new class loader for the specified jar file.  
@@ -199 +199 @@
   */
   private final Map<File, JarInfo> jarFiles;
+    
+  /**
+    Class loaders for extensions.
+  */
+  private final List<JarClassLoaderProxy> proxyLoaders;
   
   /**
@@ -232 +237 @@
     classPath = new HashMap<String, List<File>>();
     jarFiles = new HashMap<File, JarInfo>();
+    proxyLoaders = new ArrayList<JarClassLoaderProxy>();
     loadJarFile(mainJarFile, true);
   }
@@ -338 +344 @@
     
     // 2. Check the system class loader
-    if (c == null && parent != system) c = loadClassInternal(system, name);
-    if (log.isDebugEnabled()) log.debug("system class (" + name + "): " + c);
+    if (c == null && parent != system) 
+    {
+      c = loadClassInternal(system, name);
+      if (log.isDebugEnabled()) log.debug("system class (" + name + "): " + c);
+    }
     
     // 3. Delegate to parent class loader
-    if (c == null && delegateFirst) c = loadClassInternal(parent, name);
-    if (log.isDebugEnabled()) log.debug("parent class (" + name + "): " + c);
+    if (c == null && delegateFirst) 
+    {
+      c = loadClassInternal(parent, name);
+      if (log.isDebugEnabled()) log.debug("parent class (" + name + "): " + c);
+    }
 
     // 4. Look for the class in this class path
@@ -354 +366 @@
       catch (ClassNotFoundException ex)
       {}
-    }
-    if (log.isDebugEnabled()) log.debug("my class (" + name + "): " + c);
+      if (log.isDebugEnabled()) log.debug("my class (" + name + "): " + c);
+    }
     
     // 5. Delegate to parent class loader if it hasn't been done
-    if (c == null && !delegateFirst)  c = loadClassInternal(parent, name);
-    if (log.isDebugEnabled()) log.debug("parent class (" + name + "): " + c);
+    if (c == null && !delegateFirst) 
+    {
+      c = loadClassInternal(parent, name);
+      if (log.isDebugEnabled()) log.debug("parent class (" + name + "): " + c);
+    }
+    
+    // 6. Side-load from proxied JAR files (eg. other extensions)
+    Iterator<JarClassLoaderProxy> it = proxyLoaders.iterator();
+    while (c == null && it.hasNext())
+    {
+      JarClassLoaderProxy proxyLoader = it.next();
+      c = proxyLoader.findClass(name);
+      if (log.isDebugEnabled()) log.debug("proxy class (" + proxyLoader.jarPath + "; " + name + "): " + c);
+    }
     
     if (c == null)
@@ -528 +552 @@
       if (followClassPath && manifest != null)
       {
+        File directory = file.getParentFile();
         Attributes attr = manifest.getMainAttributes();
         if (attr != null)
@@ -540 +565 @@
               if (cps[i] != null && !cps[i].trim().equals(""))
               {
-                File classPathFile = new File(file.getParent(), cps[i]);
+                File classPathFile = new File(directory, cps[i]);
                 if (!classPathFile.exists())
                 {
@@ -573 +598 @@
                     }
                   }
+                  loadJarFile(classPathFile, false);
                 }
-                loadJarFile(classPathFile, false);
+                else
+                {
+                  proxyLoaders.add(new JarClassLoaderProxy(classPathFile.getAbsolutePath()));
+                }
               }
             }
@@ -728 +757 @@
     }
   }
+  
+  /**
+    A proxy class loader is typically needed when one extension
+    depends on another extension. The proxy is needed since
+    we want to use lazy initialization of the other class loaders.
+    They may not be needed immediately. The proxy will also make it
+    possible to avoid infinite recursion in case two extensions 
+    depend on each other.
+    <p>
+    
+    Once a real class loader has been aquired it will be kept 
+    until the main class loader is discared. Note that the 
+    {@link JarClassLoader#hasChanged(boolean)} is not used for 
+    automatic reloading since that may cause class-cast exceptions.
+    <p>
+    
+    The proxy is also used to limit the search for classes to 
+    classes that are directly handled directly by the other class 
+    loader. The system and parent class loaders are not searched again
+    since they are already searched in the main class loader.
+
+    @since 3.10
+  */
+  static class JarClassLoaderProxy
+  {
+    
+    final String jarPath;
+    private JarClassLoader loader;
+    private boolean isInitialized;
+    
+    /**
+      Creates a proxy class loader for the given JAR file.
+    */
+    JarClassLoaderProxy(String jarPath)
+    {
+      this.jarPath = jarPath;
+      this.isInitialized = false;
+    }
+    
+    /**
+      Initialize the proxy.
+    */
+    private synchronized void init()
+    {
+      if (isInitialized) return;
+      if (log.isDebugEnabled()) log.debug("JarClassLoaderProxy.init[" + jarPath + "]");
+      
+      try
+      {
+        loader = (JarClassLoader)JarClassLoader.getInstance(jarPath, true);
+      }
+      catch (IOException ex)
+      {}
+      isInitialized = true;
+    }
+    
+    
+    Class<?> findClass(String name)
+    {
+      if (log.isDebugEnabled()) log.debug("JarClassLoaderProxy.findClass[" + jarPath + "]: " + name);
+      if (!isInitialized) init();
+      
+      Class<?> c = null;
+      if (loader != null)
+      {
+        try
+        {
+          // 1. Check if the class has already been loaded
+          c = loader.findLoadedClass(name);
+          if (log.isDebugEnabled()) log.debug("JarClassLoaderProxy.findClass[" + jarPath + "]: loaded class (" + name + "): " + c);
+          
+          // 2. Otherwise try to load the class without searching parent or system class loaders
+          if (c == null)
+          {
+            c = loader.findClass(name);
+            if (log.isDebugEnabled()) log.debug("JarClassLoaderProxy.findClass[" + jarPath + "]: found class (" + name + "): " + c);
+          }
+        }
+        catch (ClassNotFoundException ex)
+        {}
+      }
+      return c;
+    }
+  }
 }

trunk/src/test/net/sf/basedb/test/extension/jar3/Three.java

@@ -35 +35 @@
 {
   
+  private final One one;
+  private final Two two;
+  
   public Three()
-  {}
+  {
+    this.one = new One();
+    this.two = new Two();
+  }
   
   @Override
   public String getTitle() 
   {
-    return new One().getTitle() + "+" + new Two().getTitle() + "=Three";
+    return one.getTitle() + "+" + two.getTitle() + "=Three";
   }
   
@@ -53 +59 @@
   public int getType()
   {
-    return 3;
+    return one.getType()+two.getType();
   }