Spring AOP in Programmatic Way

Spring 1.2 introduced ((AOP|Aspect Oriented Programming)) in a programmatic way. The AOP is applied by using ProxyFactory class. The factory class is provided with both the advice and the taregt.

Let's write an advice which will print a message before and after a HelloWorld program. Let's assume HelloWorld has a printMessage function.

HelloWorldDecorator

//Notice that MethodInterceptor comes from AOP alliance packages and

//not for spring framework. Spring has used the AOP alliance standards

//whereever possible

public class HelloWorldDecorator implements MethodInterceptor{

   public Object invoke(MethodInvocation methodInvocation) throws Throwable {

    System.out.print("OyeJava says ");

    Object obj = methodInvocation.proceed();

    System.out.println(" I am here");

    return obj;

  }

Now modify the main method so that we use the proxy factory to apply AOP

String[] files = {"context.xml"};

ApplicationContext appContext = new ClassPathXmlApplicationContext(files);

HelloWorld helloWorld = (HelloWorld)appContext.getBean("helloWorld");

    

//Create the proxy factory class

ProxyFactory pf = new ProxyFactory();

    

//Add the advice to it

pf.addAdvice(new HelloWorldDecorator());

//Set the target class

pf.setTarget(helloWorld);

//Get the proxy back

HelloWorld helloWorldProxy = (HelloWorld)pf.getProxy();

    

//Notice the difference between outputs.

helloWorldProxy.printMessage();    

helloWorld.printMessage();

Spring supports the following advice with the mentioned interfaces:

• Before – org.springframework.aop.MethodBeforeAdvice
• After returning – org.springframework.aop.AfterReturningAdvice
• Around – org.aopalliance.intercept.MethodInterceptor
• Throws – org.springframework.aop.ThrowsAdvice
• Introduction – org.springframework.aop.IntroductionInterceptor

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