Context ClassLoader : Class Loader « Reflection « Java Tutorial

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2. Reflection
3. Class Loader

/**************************************************************************************
 * Copyright (c) Jonas Bonr, Alexandre Vasseur. All rights reserved.                 *
 * http://aspectwerkz.codehaus.org                                                    *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the LGPL license      *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/


import java.io.InputStream;
import java.net.URL;

/**
 * Utility methods dealing with the context class loader. Fail-over is provided to the default class loader.
 *
 * @author <a href="mailto:jboner@codehaus.org">Jonas Bonr </a>
 */
public final class ContextClassLoader {

    /**
     * Loads a class starting from the given class loader (can be null, then use default class loader)
     *
     * @param loader
     * @param name   of class to load
     * @return
     * @throws ClassNotFoundException
     */
    public static Class forName(final ClassLoader loader, final String name) throws ClassNotFoundException {
        Class klass = null;
        if (loader != null) {
            klass = Class.forName(name, false, loader);
        } else {
            klass = Class.forName(name, false, ClassLoader.getSystemClassLoader());
        }
        return klass;
    }


    /**
     * Loads a class from the context class loader or, if that fails, from the default class loader.
     *
     * @param name is the name of the class to load.
     * @return a <code>Class</code> object.
     * @throws ClassNotFoundException if the class was not found.
     */
    public static Class forName(final String name) throws ClassNotFoundException {
        Class cls = null;
        try {
            cls = Class.forName(name, false, Thread.currentThread().getContextClassLoader());
        } catch (Exception e) {
            cls = Class.forName(name);
        }
        return cls;
    }

    /**
     * Loads a resource from the context class loader or, if that fails, from the default class loader.
     *
     * @param name is the name of the resource to load.
     * @return a <code>URL</code> object.
     */
    public static URL loadResource(final String name) {
        try {
            return Thread.currentThread().getContextClassLoader().getResource(name);
        } catch (Exception e) {
            return ClassLoader.class.getClassLoader().getResource(name);
        }
    }

//    /**
//     * Loads a resource from the context class loader or, if that fails, from the default class loader, as stream
//     *
//     * @param name is the name of the resource to load.
//     * @return a <code>InputStream</code> object.
//     */
//    public static InputStream getResourceAsStream(final String name) {
//        InputStream stream = null;
//        ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
//        if (contextClassLoader != null) {
//            stream = contextClassLoader.getResourceAsStream(name);
//        }
//        if (stream == null) {
//            ClassLoader classLoader = ClassLoader.class.getClassLoader();
//            if (classLoader != null) {
//                stream = classLoader.getResourceAsStream(name);
//            }
//        }
//        return stream;
//    }

    /**
     * Returns the context class loader.
     *
     * @return the context class loader
     */
    public static ClassLoader getLoader() {
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        if (loader == null) {
            loader = ClassLoader.class.getClassLoader();
        }
        return loader;
    }
}