Java: how to get arguments passed to method that c

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 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 2

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());
    }
}

Answer 3

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 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

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?