Glassfish example source code file (ASMClassFileLoader.java)

This example Glassfish source code file (ASMClassFileLoader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Glassfish tags/keywords

arraylist, asmclassfileloader, asmclassfileloader, classfile, classloader, hashmap, io, ioexception, ioexception, log, logging, net, network, noi18n, noi18n, string, string, stringtokenizer, util, weakreference

The Glassfish ASMClassFileLoader.java source code

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */

package com.sun.enterprise.tools.verifier.apiscan.classfile;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.WeakReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * *This is a factory for {@link ASMClassFile}. This is not a public class, as
 * I expect users to use {@link ClassFileLoaderFactory} interface. This class
 * internally uses the the standard Java ClassLoader to load the resource and
 * construct ASMClassFile object out of it.
 *
 * @author Sanjeeb.Sahoo@Sun.COM
 */
class ASMClassFileLoader implements ClassFileLoader {

    private ClassLoader cl;
    private static String resourceBundleName = "com.sun.enterprise.tools.verifier.apiscan.LocalStrings";
    private static Logger logger = Logger.getLogger("apiscan.classfile", resourceBundleName); // NOI18N
    private final static String myClassName = "ASMClassFileLoader"; // NOI18N
    // cache of already loaded classes
    private Map<String, WeakReference loadedClassesCache =
            new HashMap<String, WeakReference();
    /**
     * Creates a new instance of ASMClassFileLoader.
     *
     * @param cp that will be used to create a new java.net.URLClassLoader. In
     *           subsequent load operations, this classloader will be used.
     */
    public ASMClassFileLoader(String cp) {
        ArrayList<URL> urls = new ArrayList();
        for (StringTokenizer st = new StringTokenizer(cp, File.pathSeparator);
             st.hasMoreTokens();) {
            String entry = st.nextToken();
            try {
                urls.add(new File(entry).toURI().toURL());
            } catch (MalformedURLException e) {
                logger.logp(Level.WARNING, myClassName, "init<>", getClass().getName() + ".exception1", new Object[]{entry});
                logger.log(Level.WARNING, "", e);
            }
        }
        //We do not want system class loader or even extension class loadera s our parent.
        //We want only boot class loader as our parent. Boot class loader is represented as null.
        cl = new URLClassLoader((URL[]) urls.toArray(new URL[0]), null);
    }

    /**
     * Creates a new instance of ASMClassFileLoader.
     *
     * @param cl is the classloader that will be used in subsequent load
     *           operations.
     */
    public ASMClassFileLoader(ClassLoader cl) {
        this.cl = cl;
    }

    //See corresponding method of ClassFileLoader
    public ClassFile load(String externalClassName) throws IOException {
        logger.entering("ASMClassFileLoader", "load", externalClassName); // NOI18N
        WeakReference<ClassFile> cachedCF = loadedClassesCache.get(externalClassName);
        if(cachedCF!=null){
            ClassFile cf = cachedCF.get();
            if(cf!=null){
                return cf;
            } else {
                logger.logp(Level.FINE, "ASMClassFileLoader", "load", // NOI18N
                        "{0} has been garbage collected from cache!", externalClassName); // NOI18N
            }
        }
        return load0(externalClassName);
    }

    private ClassFile load0(String externalClassName) throws IOException {
        //URLClassLoader library expects me to pass in internal form.
        String internalClassName = externalClassName.replace('.', '/');
        InputStream is = cl.getResourceAsStream(internalClassName + ".class");
        //URLClassLoader returns null if resource is not found.
        if (is == null) throw new IOException(
                "Not able to load " + internalClassName + ".class");
        try {
            ClassFile cf = new ASMClassFile(is);
            matchClassSignature(cf, externalClassName);
            loadedClassesCache.put(externalClassName,
                    new WeakReference<ClassFile>(cf));
            return cf;
        } finally {
            is.close();
        }

    }

    //This method is neede to be protected against users who are passing us
    //internal class names instead of external class names or
    //when the file actually represents some other class, but it isnot
    //available in in proper package hierarchy.
    private void matchClassSignature(ClassFile cf, String externalClassName)
            throws IOException {
        String nameOfLoadedClass = cf.getName();
        if (!nameOfLoadedClass.equals(externalClassName)) {
            throw new IOException(externalClassName + ".class represents " +
                    cf.getName() +
                    ". Perhaps your package name is incorrect or you passed the " +
                    "name using internal form instead of using external form.");
        }
    }
}