groovy-core/src/main/org/codehaus/groovy/runtime/metaclass/ReflectorLoader.java

/*
 * Copyright 2003-2007 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.runtime.metaclass;

import org.codehaus.groovy.runtime.Reflector;

import java.security.ProtectionDomain;
import java.util.HashMap;
import java.util.Map;

/**
 * Reflector creation helper. This class is used to define the Refloctor classes.
 * For each ClassLoader such a loader will be created by MetaClass.
 * Special about this loader is, that it knows the classes form the 
 * Groovy Runtime. The Reflector class is resolved in different ways: During
 * the definition of a class Reflector will resolve to the Reflector class of
 * the runtime, even if there is another Reflector class in the parent loader.
 * After the new class is defined Reflector will resolve like other Groovy
 * classes. This loader is able to resolve all Groovy classes even if the
 * parent does not know them, but the parent serves first (Reflector during a
 * class defintion is different). 
 * 
 * @author <a href="mailto:blackdrag@gmx.org">Jochen Theodorou</a>
 * @version $Revision$
 */
public class ReflectorLoader extends ClassLoader {
    private boolean inDefine = false;
    private final Map loadedClasses = new HashMap();
    private final ClassLoader delegatationLoader;

    private static final String REFLECTOR = Reflector.class.getName();
    
    /**
     * Tries to find a Groovy class.
     * 
     * @return the class if found
     * @throws ClassNotFoundException if not found
     */
    protected Class findClass(String name) throws ClassNotFoundException {
        if (delegatationLoader==null) return super.findClass(name);
        return delegatationLoader.loadClass(name);
    }
    
    /**
     * Loads a class per name. Unlike a normal loadClass this version
     * behaves different during a class definition. In that case it
     * checks if the class we want to load is Reflector and returns 
     * class if the check is successful. If it is not during a class
     * definition it just calls the super class version of loadClass. 
     * 
     * @param name of the class to load
     * @param resolve is true if the class should be resolved
     * @see Reflector
     * @see ClassLoader#loadClass(String, boolean)
     */
    protected synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
        if (inDefine) {
            if (name.equals(REFLECTOR)) return Reflector.class;
        }
        return super.loadClass(name, resolve);
    }
    
    /**
     * helper method to define Reflector classes.
     * @param name of the Reflector
     * @param bytecode the bytecode
     * @param domain  the protection domain
     * @return the generated class
     */
    public synchronized Class defineClass(String name, byte[] bytecode, ProtectionDomain domain) {
        inDefine = true;
        Class c = defineClass(name, bytecode, 0, bytecode.length, domain);
        loadedClasses.put(name,c); 
        resolveClass(c);
        inDefine = false;
        return c;
    }
    
    /**
     * creates a RelfectorLoader. 
     * @param parent the parent loader. This should never be null!
     */
    public ReflectorLoader(ClassLoader parent) {
        super(parent);
        delegatationLoader = getClass().getClassLoader();
    }
    
    /**
     * try to load one of the defined Reflector classes by name.
     * @param name of the Reflector class
     * @return the Reflector class if defined else null.
     */
    public synchronized Class getLoadedClass(String name) {
        return (Class)loadedClasses.get(name);
    }
}