org.directwebremoting.util.MethodMatchingProxyFactory Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of dwr Show documentation

DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boiler plate code between the web browser and your Java code.

The newest version!

/*
 * Copyright 2005 Joe Walker
 *
 * 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.directwebremoting.util;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

/**
 * A proxy generator that allows mapping a backing class to an interface it doesn't implement as long as method signatures match.
 *
 * @author Mike Wilson
 */
public class MethodMatchingProxyFactory
{
    public static  T createProxy(Class interfaceClass, Class backingClass, Object... constructorArgs)
    {
        try
        {
            // Instantiate backing class object
            Object backingObject;
            if (constructorArgs.length == 0 && backingClass.getConstructors().length == 0) {
                // Default constructor
                backingObject = backingClass.newInstance();
            } else {
                // Look up explicit constructor
                Class[] backingArgsClasses = new Class[constructorArgs.length];
                for(int i=0; i ctor = backingClass.getConstructor(backingArgsClasses);
                backingObject = ctor.newInstance(constructorArgs);
            }

            // Wrap with a proxy conforming to the fronting interface
            Object proxy = Proxy.newProxyInstance(MethodMatchingProxyFactory.class.getClassLoader(), new Class[]{interfaceClass}, new MethodMatchingInvocationHandler(backingObject));
            return interfaceClass.cast(proxy);
        }
        catch (Exception ex)
        {
            if (ex instanceof RuntimeException) {
                RuntimeException rex = (RuntimeException) ex;
                throw rex;
            } else {
                throw new RuntimeException(ex);
            }
        }
    }

    private static class MethodMatchingInvocationHandler implements InvocationHandler
    {
        private final Object backingObject;

        public MethodMatchingInvocationHandler(Object backingObject)
        {
            this.backingObject = backingObject;
        }

        public Object invoke(Object proxy, Method proxyMethod, Object[] args) throws Throwable
        {
            try {
                Method backingMethod = backingObject.getClass().getMethod(proxyMethod.getName(), proxyMethod.getParameterTypes());
                return backingMethod.invoke(backingObject, args);
            } catch(NoSuchMethodException ex) {
                throw new RuntimeException("Method '" + proxyMethod.getName() + "' not implemented in " + backingObject.getClass().getName() + ".");
            }
        }
    }
}