org.ops4j.pax.web.service.spi.util.ResourceDelegatingBundleClassLoader.java Source code

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Here is the source code for org.ops4j.pax.web.service.spi.util.ResourceDelegatingBundleClassLoader.java

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/*
 * Copyright 2013 Harald Wellmann
 *
 * Licensed  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.ops4j.pax.web.service.spi.util;

import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.List;
import java.util.Vector;

import org.apache.commons.collections4.map.LRUMap;
import org.ops4j.pax.swissbox.core.BundleClassLoader;
import org.osgi.framework.Bundle;

/**
 * A bundle class loader which delegates resource loading to a list of delegate
 * bundles.
 *
 * @author Harald Wellmann
 */
public class ResourceDelegatingBundleClassLoader extends BundleClassLoader {

    private List<Bundle> bundles;

    private int cacheSize = 100; //equals the default size of the LRUMap, might be changed in a later version.

    private LRUMap<String, Vector<URL>> lruCache = new LRUMap<>(cacheSize);

    public ResourceDelegatingBundleClassLoader(List<Bundle> bundles) {
        super(bundles.get(0));
        this.bundles = bundles;
    }

    public ResourceDelegatingBundleClassLoader(List<Bundle> bundles, ClassLoader parent) {
        super(bundles.get(0), parent);
        this.bundles = bundles;
    }

    public void addBundle(Bundle bundle) {
        bundles.add(bundle);
        lruCache.clear();
    }

    public List<Bundle> getBundles() {
        return bundles;
    }

    protected URL findResource(String name) {
        Vector<URL> resources = getFromCache(name);

        if (resources == null) {
            resources = new Vector<>();
            for (Bundle delegate : bundles) {
                try {
                    URL resource = delegate.getResource(name);
                    if (resource != null) {
                        resources.add(resource);
                        break;
                    }
                } catch (IllegalStateException exc) {
                    // ignore
                }
            }
            if (!resources.isEmpty()) {
                addToCache(name, resources);
            }
        }

        Enumeration<URL> elements = resources.elements();
        if (elements.hasMoreElements()) {
            return elements.nextElement();
        }
        return null;
    }

    @Override
    protected Enumeration<URL> findResources(String name) throws IOException {
        Vector<URL> resources = getFromCache(name);

        if (resources == null) {
            resources = new Vector<>();
            for (Bundle delegate : bundles) {
                try {
                    Enumeration<URL> urls = delegate.getResources(name);
                    if (urls != null) {
                        while (urls.hasMoreElements()) {
                            resources.add(urls.nextElement());
                        }
                    }
                } catch (IllegalStateException exc) {
                    // ignore
                }
            }
            if (!resources.isEmpty()) {
                addToCache(name, resources);
            }
        }

        return resources.elements();
    }

    protected synchronized void addToCache(String name, Vector<URL> resources) {
        lruCache.put(name, resources);
    }

    protected Vector<URL> getFromCache(String name) {
        return lruCache.get(name);
    }
}