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:
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 | 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.
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