codetroopers.wicket.HotReloadingClassResolver.java Source code

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Here is the source code for codetroopers.wicket.HotReloadingClassResolver.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 codetroopers.wicket;

import org.apache.wicket.Application;
import org.apache.wicket.WicketRuntimeException;
import org.apache.wicket.application.IClassResolver;
import org.apache.wicket.util.collections.UrlExternalFormComparator;

import java.lang.ref.WeakReference;
import java.net.URL;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

/**
 * @author <a href="mailto:cedric@gatay.fr">cgatay</a>
 * This class is copied from Wicket's sources as resolveClass is final
 *
 ************************************************************************
 *
 * An abstract implementation of a {@link org.apache.wicket.application.IClassResolver} which uses a {@link ClassLoader} for
 * resolving classes.
 *
 * @see org.apache.wicket.settings.IApplicationSettings#getClassResolver()
 *
 * @author Juergen Donnerstag
 * @author Jonathan Locke
 */
public class HotReloadingClassResolver 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 ConcurrentMap<String, WeakReference<Class<?>>> classes = new ConcurrentHashMap<String, WeakReference<Class<?>>>();

    @Override
    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 {
                // synchronize on the only class member to load only one class at a time and
                // prevent LinkageError. See above for more info
                synchronized (classes) {
                    clazz = getClassLoader().loadClass(className);
                    if (clazz == null) {
                        throw new ClassNotFoundException(className);
                    }
                }
                classes.put(className, new WeakReference<Class<?>>(clazz));
            }
        }
        return clazz;
    }

    @Override
    public Iterator<URL> getResources(final String name) {
        Set<URL> resultSet = new TreeSet<URL>(new UrlExternalFormComparator());

        try {
            // Try the classloader for the wicket jar/bundle
            Enumeration<URL> resources = Application.class.getClassLoader().getResources(name);
            loadResources(resources, resultSet);

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

            // Try the context class loader
            resources = getClassLoader().getResources(name);
            loadResources(resources, resultSet);
        } catch (Exception e) {
            throw new WicketRuntimeException(e);
        }

        return resultSet.iterator();
    }

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

    /**
     * {@inheritDoc}
     *
     * @return the current {@link Thread}s context {@link ClassLoader} if it is set, or the
     *         {@link ClassLoader} that was used to load this class.
     */
    @Override
    public ClassLoader getClassLoader() {
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        if (loader == null) {
            loader = getClass().getClassLoader();
        }
        return loader;
    }
}