com.mgmtp.perfload.core.client.lang.LocalFirstClassLoader.java Source code

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Here is the source code for com.mgmtp.perfload.core.client.lang.LocalFirstClassLoader.java

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/*
 * Copyright (c) 2002-2014 mgm technology partners GmbH
 *
 * 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 com.mgmtp.perfload.core.client.lang;

import java.net.URL;
import java.net.URLClassLoader;

import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;

/**
 * {@link URLClassLoader} implementation that tries to load classes locally before delegating to the
 * parent class loader. This is necessary for plugin-like architectures where a class and its
 * dependencies need to be loaded in isolation.
 * 
 * @author rnaegele
 */
public final class LocalFirstClassLoader extends URLClassLoader {

    /**
     * @param urls
     *            The URLs making up the local classpath for this class loader.
     */
    public LocalFirstClassLoader(final URL... urls) {
        super(urls);
    }

    /**
     * Loads the class with the specified binary name trying to load it from the local classpath
     * first before delegating to the normal class loading mechanism.
     */
    @Override
    protected synchronized Class<?> loadClass(final String name, final boolean resolve)
            throws ClassNotFoundException {
        // Check if the class has already been loaded
        Class<?> loadedClass = findLoadedClass(name);

        if (loadedClass == null) {
            try {
                // First try to find it locally
                loadedClass = findClass(name);
            } catch (ClassNotFoundException e) {
                // Swallow exception --> the class does not exist locally
            }

            // If the class is not found locally we delegate to the normal class loading mechanism
            if (loadedClass == null) {
                loadedClass = super.loadClass(name, resolve);
            }
        }

        if (resolve) {
            resolveClass(loadedClass);
        }
        return loadedClass;
    }

    /**
     * Finds the resource with the given name trying to load it from the local classpath first
     * before delegating to the normal resource loading mechanism.
     */
    @Override
    public URL getResource(final String name) {
        // First try to find it locally
        URL url = findResource(name);

        // If the resource is not found locally we delegate to the normal resource loading mechanism
        if (url == null) {
            url = super.getResource(name);
        }

        return url;
    }

    @Override
    public String toString() {
        ToStringBuilder tsb = new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE);
        URL[] urls = getURLs();
        tsb.append("urls", urls);
        return tsb.toString();
    }
}