Java ASM 字节码操作 - 如何在方法中间注入？

Question

Using ASM, how can i inject a method exactly where I want it to go?

example:

public void exampleMethod() {
    doOneThing();
    doSomeMoreStuff();

    if (someCondition) {
        doEvenMoreThings();
    }

    callMyInjectedMethodHere(); // This call has been injected

    if (someOtherCondition) {
        doRandomStuff();
    }

    doStuff();
}

Answer 1

ASM has a visitor and a tree API which allows you to process a method's byte code instruction by instruction. What you would need to do would be to visit all instructions, in your case two method calls, a branching instruction, a method call and a label that is the target of the previous branch and then emitt an additional method call instruction. This way, you can modify the method.

Do however notice that method bodies typically change more rapidly then signatures and that such injections tend to be very fragile. If you can avoid it, avoid it.