loaderclasspath.java

Javassist是一个开源的分析、编辑和创建Java字节码的类库。是由东京技术学院的数学和计算机科学系的 Shigeru Chiba 所创建的。它已加入了开放源代码JBoss 应用服务器项目,通过使

/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999-2006 Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package javassist;

import java.io.InputStream;
import java.net.URL;
import java.lang.ref.WeakReference;

/**
 * A class search-path representing a class loader.
 *
 * <p>It is used for obtaining a class file from the given
 * class loader by <code>getResourceAsStream()</code>.
 * The <code>LoaderClassPath</code> refers to the class loader through
 * <code>WeakReference</code>.  If the class loader is garbage collected,
 * the other search pathes are examined.
 *
 * <p>The given class loader must have both <code>getResourceAsStream()</code>
 * and <code>getResource()</code>.
 *
 * @author <a href="mailto:[e-mail]">Bill Burke</a>
 * @author Shigeru Chiba
 *
 * @see ClassPool#insertClassPath(ClassPath)
 * @see ClassPool#appendClassPath(ClassPath)
 * @see ClassClassPath
 */
public class LoaderClassPath implements ClassPath {
    private WeakReference clref;

    /**
     * Creates a search path representing a class loader.
     */
    public LoaderClassPath(ClassLoader cl) {
        clref = new WeakReference(cl);
    }

    public String toString() {
        Object cl = null;
        if (clref != null)
            cl = clref.get();

        return cl == null ? "<null>" : cl.toString();
    }

    /**
     * Obtains a class file from the class loader.
     * This method calls <code>getResourceAsStream(String)</code>
     * on the class loader.
     */
    public InputStream openClassfile(String classname) {
        String cname = classname.replace('.', '/') + ".class";
        ClassLoader cl = (ClassLoader)clref.get();
        if (cl == null)
            return null;        // not found
        else
            return cl.getResourceAsStream(cname);
    }

    /**
     * Obtains the URL of the specified class file.
     * This method calls <code>getResource(String)</code>
     * on the class loader.
     *
     * @return null if the class file could not be found. 
     */
    public URL find(String classname) {
        String cname = classname.replace('.', '/') + ".class";
        ClassLoader cl = (ClassLoader)clref.get();
        if (cl == null)
            return null;        // not found
        else
            return cl.getResource(cname);
    }

    /**
     * Closes this class path.
     */
    public void close() {
        clref = null;
    }
}