Adding hook without changing source code

Question

Is it possible to add a hook to a meothd without changing the method? For example:

public class class1{ 
    public void method1(){}
}
public class class2{
    public void method2(){}
}

Now how can I execute method2() everytime when method1() is executed, without changing anything in class1?

Answer 1

This is known as AOP or Aspect Oriented Programming, and is implemented via bytecode manipulation.

Spring includes facilities for AOP.

A detailed description of AOP would be too long for StackOverflow, and redundant since there are many good resources on the web.

Answer 2

Use 'Decorator pattern' to extend functionality of class1. This approach requires change in code that calls class1