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EasyMock provides an easy way to create Mock Objects for interfaces and classes generating them on the fly
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/*
 * Copyright 2003,2004 The Apache Software Foundation
 *
 *  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.easymock.cglib.proxy;

import java.io.Serializable;
import java.lang.reflect.Method;
import java.lang.reflect.Member;
import org.easymock.cglib.core.CodeGenerationException;

/**
 * This class is meant to be used as replacement for
 * java.lang.reflect.Proxy under JDK 1.2. There are some known
 * subtle differences:
 * 
 * The exceptions returned by invoking getExceptionTypes
 * on the Method passed to the invoke method
 * are the exact set that can be thrown without resulting in an
 * UndeclaredThrowableException being thrown.
 * 
{@link UndeclaredThrowableException} is used instead
 * of java.lang.reflect.UndeclaredThrowableException.
 * 
 * 
 * @version $Id: Proxy.java,v 1.6 2004/06/24 21:15:19 herbyderby Exp $
 */
public class Proxy implements Serializable {
    protected InvocationHandler h;

    private static final CallbackFilter BAD_OBJECT_METHOD_FILTER = new CallbackFilter() {
        public int accept(Method method) {
            if (method.getDeclaringClass().getName().equals("java.lang.Object")) {
                String name = method.getName();
                if (!(name.equals("hashCode") ||
                      name.equals("equals") ||
                      name.equals("toString"))) {
                    return 1;
                }
            }
            return 0;
        }
    };

    protected Proxy(InvocationHandler h) {
        Enhancer.registerCallbacks(getClass(), new Callback[]{ h, null });
        this.h = h;
    }

    // private for security of isProxyClass
    private static class ProxyImpl extends Proxy {
        protected ProxyImpl(InvocationHandler h) {
            super(h);
        }
    }

    public static InvocationHandler getInvocationHandler(Object proxy) {
        if (!(proxy instanceof ProxyImpl)) {
            throw new IllegalArgumentException("Object is not a proxy");
        }
        return ((Proxy)proxy).h;
    }

    public static Class getProxyClass(ClassLoader loader, Class[] interfaces) {
        Enhancer e = new Enhancer();
        e.setSuperclass(ProxyImpl.class);
        e.setInterfaces(interfaces);
        e.setCallbackTypes(new Class[]{
            InvocationHandler.class,
            NoOp.class,
        });
        e.setCallbackFilter(BAD_OBJECT_METHOD_FILTER);
        e.setUseFactory(false);
        return e.createClass();
    }

    public static boolean isProxyClass(Class cl) {
        return cl.getSuperclass().equals(ProxyImpl.class);
    }

    public static Object newProxyInstance(ClassLoader loader, Class[] interfaces, InvocationHandler h) {
        try {
            Class clazz = getProxyClass(loader, interfaces);
            return clazz.getConstructor(new Class[]{ InvocationHandler.class }).newInstance(new Object[]{ h });
        } catch (RuntimeException e) {
            throw e;
        } catch (Exception e) {
            throw new CodeGenerationException(e);
        }
    }
}