With this example we are going to demonstrate how to create a Proxy object. A proxy is a class functioning as an interface to a network connection, a large object in memory, a file, or some other resource that is expensive or impossible to duplicate. In short, to create a Proxy object we have followed the steps below:
- We have created an interface,
MyInterfacewith a method and the implementation of the interface,MyInterfaceImpl. - We have created
MyProxyclass,that implements the InvocationHandler. It has an Object o and a constructor where it initializes its object. It also has a method,Object invoke(Object proxy, Method m, Object[] args), that usesinvoke(Object obj, Object... args)API method of Method to get the underlying method represented by this Method object, on the specified object with the specified parameters and returns this result. - We create an instance of a proxy class for the specified interface that dispatches method invocations to the specified invocation handler, using
newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h)API method of Proxy. - Then we invoke the method of the object.
Let’s take a look at the code snippet that follows:
package com.javacodegeeks.snippets.core;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class CreateProxyObject {
public static void main(String[] args) {
// return an instance of a proxy class for the specified interfaces
// that dispatches method invocations to the specified invocation handler
MyInterface myintf = (MyInterface)Proxy.newProxyInstance(
MyInterface.class.getClassLoader(),
new Class[]{MyInterface.class},
new MyProxy(new MyInterfaceImpl())
);
// Invoke the method
myintf.method();
}
private static interface MyInterface {
void method();
}
private static class MyInterfaceImpl implements MyInterface {
public void method() {
System.out.println("Plain method is invoked");
}
}
private static class MyProxy implements InvocationHandler {
Object obj;
public MyProxy(Object o) {
obj = o;
}
public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
Object result = null;
try {
System.out.println("Proxy Class is called before method invocation");
result = m.invoke(obj, args);
}
catch (InvocationTargetException e) {
System.out.println("Invocation Target Exception: " + e);
}
catch (Exception e) {
System.out.println("Invocation Target Exception: " + e);
}
finally {
System.out.println("Proxy Class is called after method invocation");
}
return result;
}
}
}
Output:
Proxy Class is called before method invocation
Plain method is invoked
Proxy Class is called after method invocation
This was an example of how to create a Proxy object in Java.
