org.cipango.ims.oam.util.ClassResolver.java Source code

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Here is the source code for org.cipango.ims.oam.util.ClassResolver.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.cipango.ims.oam.util;

import java.io.IOException;
import java.lang.ref.WeakReference;
import java.net.URL;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.wicket.Application;
import org.apache.wicket.WicketRuntimeException;
import org.apache.wicket.application.DefaultClassResolver;
import org.apache.wicket.application.IClassResolver;

public class ClassResolver implements IClassResolver {
    /**
     * Usually class loaders implement more efficient caching strategies than we could possibly do,
     * but we experienced synchronization issue resulting in stack traces like:
     * java.lang.LinkageError: duplicate class definition:
     * 
     * <pre>
     *    wicket/examples/repeater/RepeatingPage at java.lang.ClassLoader.defineClass1(Native Method) 
     * </pre>
     * 
     * This problem has gone since we synchronize the access.
     */
    private final ConcurrentHashMap<String, WeakReference<Class<?>>> classes = new ConcurrentHashMap<String, WeakReference<Class<?>>>();

    /**
     * @see org.apache.wicket.application.IClassResolver#resolveClass(java.lang.String)
     */
    public final Class<?> resolveClass(final String classname) throws ClassNotFoundException {
        Class<?> clazz = null;
        WeakReference<Class<?>> ref = classes.get(classname);

        // Might be garbage-collected between getting the WeakRef and retrieving
        // the Class from it.
        if (ref != null) {
            clazz = ref.get();
        }
        if (clazz == null) {
            if (classname.equals("byte")) {
                clazz = byte.class;
            } else if (classname.equals("short")) {
                clazz = short.class;
            } else if (classname.equals("int")) {
                clazz = int.class;
            } else if (classname.equals("long")) {
                clazz = long.class;
            } else if (classname.equals("float")) {
                clazz = float.class;
            } else if (classname.equals("double")) {
                clazz = double.class;
            } else if (classname.equals("boolean")) {
                clazz = boolean.class;
            } else if (classname.equals("char")) {
                clazz = char.class;
            } else if (classname.equals("[B")) {
                clazz = byte[].class;
            } else {
                synchronized (classes) {
                    ClassLoader loader = Thread.currentThread().getContextClassLoader();
                    if (loader == null) {
                        loader = DefaultClassResolver.class.getClassLoader();
                    }
                    clazz = loader.loadClass(classname);
                }
                classes.put(classname, new WeakReference<Class<?>>(clazz));
            }
        }
        return clazz;
    }

    /**
     * 
     * @see org.apache.wicket.application.IClassResolver#getResources(java.lang.String)
     */
    public Iterator<URL> getResources(String name) {
        HashSet<URL> loadedFiles = new HashSet<URL>();
        try {
            // Try the classloader for the wicket jar/bundle
            Enumeration<URL> resources = Application.class.getClassLoader().getResources(name);
            loadResources(resources, loadedFiles);

            // Try the classloader for the user's application jar/bundle
            resources = Application.get().getClass().getClassLoader().getResources(name);
            loadResources(resources, loadedFiles);

            // Try the context class loader
            resources = Thread.currentThread().getContextClassLoader().getResources(name);
            loadResources(resources, loadedFiles);
        } catch (IOException e) {
            throw new WicketRuntimeException(e);
        }

        return loadedFiles.iterator();
    }

    /**
     * 
     * @param resources
     * @param loadedFiles
     */
    private void loadResources(Enumeration<URL> resources, Set<URL> loadedFiles) {
        if (resources != null) {
            while (resources.hasMoreElements()) {
                final URL url = resources.nextElement();
                if (!loadedFiles.contains(url)) {
                    loadedFiles.add(url);
                }
            }
        }
    }
}