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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boilerplate code between the web browser and your Java code. This version 4.0.2 works with Jakarta Servlet 4.0.2.

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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.getDeclaredConstructor().newInstance();
            } else {
                // Look up explicit constructor
                Class[] backingArgsClasses = new Class[constructorArgs.length];
                for(int i=0; i constructor = backingClass.getConstructor(backingArgsClasses);
                backingObject = constructor.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) {
                throw (RuntimeException) ex;
            } 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() + ".");
            }
        }
    }
}