在运行时更改方法执行（Java）

Question

I am a Software Engineer in Test, and I am trying to write code that can replace production side method so that test can execute those instead. Basically, I do not want to modify production code for testability.

Here is a simple scenario:

public class Foo {

     public static void foo() {
         printA();
     }

     public static void printA() {
         System.out.println("A");
     }

     public static void printB() {
         System.out.println("B");
     }
}

public class Foobar {

    public Foobar() {

    }

    public void test() {
        Foo.foo();
    }

    public static void main(String[] args) {
        //Try changing the method here

        new Foobar().test();
    }

}

As you can see, when the main executes, it will print "A" since it calls the method printA on static method foo(). Now on runtime, is there a way I can inject or modify such that foo will call printB instead of printA?

Thank you for all the help!

Answer 1

Look at AspectJ .

It provides advices , which can be used to execute some code around a method (before and after its execution), including bypassing the call to original method altogether and returning some arbirary value

Answer 2

If you're just doing this for testing out classes, you could use a mocking framework to mock the classes on the server. I like Mockito .

Answer 3

您可以使用java反射api自己完成操作，也可以使用PowerMock之类的工具。