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Groovy example source code file (SunClassLoader.java)

This example Groovy source code file (SunClassLoader.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 - Groovy tags/keywords

class, class, classloader, classnotfoundexception, classreader, classreader, classwriter, io, map, security, string, sunclassloader, sunclassloader, throwable, throwable, util, v

The Groovy SunClassLoader.java source code

/*
 * Copyright 2003-2009 the original author or authors.
 *
 * 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.codehaus.groovy.reflection;

import org.objectweb.asm.Opcodes;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.ClassReader;

import java.util.Map;
import java.util.HashMap;
import java.io.IOException;
import java.io.InputStream;
import java.security.AccessController;
import java.security.PrivilegedAction;

/**
 * Special class loader, which when running on Sun VM allows to generate accessor classes for any method
 */
public class SunClassLoader extends ClassLoader implements Opcodes {
    protected final Map<String,Class> knownClasses = new HashMap();

    protected static final SunClassLoader sunVM;

    static {
        SunClassLoader res;
        try {
            res = AccessController.doPrivileged(new PrivilegedAction<SunClassLoader>() {
                public SunClassLoader run() {
                    try {
                        return new SunClassLoader();
                    } catch (Throwable e) {
                        return null;
                    }
                }
            });
        }
        catch (Throwable e) {
            res = null;
        }
        sunVM = res;
    }

    protected SunClassLoader() throws Throwable {
        super (SunClassLoader.class.getClassLoader());

        final Class magic = ClassLoader.getSystemClassLoader().loadClass("sun.reflect.MagicAccessorImpl");
        knownClasses.put("sun.reflect.MagicAccessorImpl", magic);
        loadMagic ();
    }

    private void loadMagic() {
        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
        cw.visit(Opcodes.V1_4, Opcodes.ACC_PUBLIC, "sun/reflect/GroovyMagic", null, "sun/reflect/MagicAccessorImpl", null);
        MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null);
        mv.visitCode();
        mv.visitVarInsn(ALOAD, 0);
        mv.visitMethodInsn(INVOKESPECIAL, "sun/reflect/MagicAccessorImpl", "<init>", "()V");
        mv.visitInsn(RETURN);
        mv.visitMaxs(0,0);
        mv.visitEnd();
        cw.visitEnd();

        define(cw.toByteArray(), "sun.reflect.GroovyMagic");
    }

    protected void loadFromRes(String name) throws IOException {
        final InputStream asStream = SunClassLoader.class.getClassLoader().getResourceAsStream(resName(name));
        ClassReader reader = new ClassReader(asStream);
        final ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
        reader.accept(cw, ClassWriter.COMPUTE_MAXS);
        asStream.close();
        define(cw.toByteArray(), name);
    }

    protected static String resName(String s) {
        return s.replace('.','/') + ".class";
    }

    protected void define(byte[] bytes, final String name) {
        knownClasses.put(name, defineClass(name, bytes, 0, bytes.length));
    }

    protected synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
        final Class aClass = knownClasses.get(name);
        if (aClass != null)
          return aClass;
        else {
            try {
                return super.loadClass(name, resolve);
            }
            catch (ClassNotFoundException e) {
                return getClass().getClassLoader().loadClass(name);
            }
        }
    }

    public Class doesKnow(String name) {
        return knownClasses.get(name);
    }
}

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