Java: how to get arguments passed to method that called this method?

Question

In java, it is possible to get the class and method that called the current method (the method in which you get the StackTrace).

My question is, can I get the arguments that were passed to the method that called this method?

I need this for debugging purposes.

Eg:

baseClass {
   initialFunc(input) {
       var modifiedInput = input + " I modified you";
       otherClass.doSomething(modifiedInput);
   }
}

otherClass {
    doSomething(input)  {
         //GET THE ARGUMENTS PASSED TO THE METHOD OF THE CLASS THAT CALLED THIS METHOD
    }
}

Can one get this information from the stacktrace, or are there other means?

(Note that I need to be able to do this in runtime and cannot actually change the source of baseClass, this is going to be a feature of my debugging class that does not know the source beforehand)

Thanks.

Answer 1

I don't believe this is possible using the standard Java API.

What you could do is to use AspectJ, place a point-cut at the calling method, save the arguments, place a point-cut at the called method and pass on the arguments.

Another option (slightly more advanced) is to use a custom, bytecode-rewriting, class loader that saves the original arguments, and passes them on as extra arguments to the next method. This would probably take a day or two to implement. Suitable frameworks are BCEL or ASM.

Answer 2

I think this could be possible, because input is out of scope but isn't yet accessible for garbage collection, so the value still exists, but unfortunately I don't believe there is an default API way to access it. This could be maybe possible with a custom implemented NDC (nested diagnostic context) for the logging approach.

Answer 3

I'm not sure why you'd ever want to do this in Java?

The only way I can think of is to create a custom wrapper object for the passed string, thus sending the reference to the wrapper instead of a new string each time.
I'd advice against it, though, since it clutters your original code, and makes it even more error prone.

Might this problem not be solved using a debugger, like the one built into eclipse, to inspect your state?

Answer 4

You can get name of caller method and its class, but you have to add some code in current method:

    public static void main(String[] args) throws Exception {
    call();
}

private static void call() {
    Exception exception = new Exception();
    for(StackTraceElement trace : exception.getStackTrace()){
        System.out.println(trace.getMethodName());
    }
}

This will print "call" and "main", methods name in called order (reverse).

Answer 5

This is possible using Reflection API !

public class StackTrace {
    public static void main(String args[]) {
        StackTrace st = new StackTrace();
        st.func();
    }
    public void func() {
        OtherClass os =new OtherClass();
        os.getStackTrace(this);
    }
}

class OtherClass {
    void getStackTrace(Object obj)  {
        System.out.println(obj.getClass());
    }
}