Java : Getting the currently executing Method corresponding object

Question

What is the most elegant way to get the currently executing method as a Method object ?

My first obvious way to do it would be to use a static method in a helper class, which would load the current thread stack, get the right stack trace element, and construct the Method element from its information.

Is there a more elegant way to achieve this?

Answer 1

This topic is covered in deeper depth in this SO Question.

I need to do the same thing and I found the best solution to be the one provided by @alexsmail.

It seems a little bit hacky but the general idea is that you declare a local class in the method and then take advantage of class.getEnclosingMethod();

Code slightly modified from @alexsmail's solution:

public class SomeClass {
   public void foo(){
      class Local {};
      Method m = Local.class.getEnclosingMethod();
   }
 }

Answer 2

Out of the box, I'm not aware of a better way to do this.

One thing to consider perhaps would be aspects - you could weave an aspect into the code that fired around all method invocations and pushed the current Method object to a ThreadLocal (based on the reflective information available from the joinpoint).

This would be probably prohibitively expensive if it really fired on all methods, but depending on what you're doing with the results, you may be able to constrain the capturing down to certain packages/classes, which would help. You may be able to defer the actual lookup of the Method too until such time as it's used, and instead store the name of the method and arguments etc.

I have my doubts whether there's going to be a particularly cheap way to achieve this, though.

Answer 3

I find that this works well:

package com.paintedintel.util;

public class Log{

    public static void out(final String output) {
        System.out.println(output);
    }
    
    public static void debug(String output) {
        System.err.println(Log.currentLocation() + " " + output);
    }
    
    public static String currentLocation() {
        StackTraceElement classMethod = new Throwable() 
                .getStackTrace()[2];
        String   currMethod = classMethod.getMethodName(); 
        String   fullClass  = classMethod.getClassName();
        String[] smplClass  = fullClass.split("\\.");
        return smplClass[smplClass.length - 1] + "." + currMethod;
    }   
}

You can call it as

Log.debug("my message " + myParameters);

I have it printing out the simpleClassName() rather than the package class name which you can't get at directly which is the

split("\\."); //yes you need to escape the "."

Other than that, it can track where you're debug output is coming from automatically. Or you could just use it to get the method and class names.

If you combine the debug and currentLocation methods you'll have to use a lower index to get the line you want....

        StackTraceElement classMethod = new Throwable() 
                .getStackTrace()[2]; // use a different index [x] w/exr methods

Answer 4

If you are using Java 9+ then you can use StackWalker:

public void foo() {
    StackWalker walker = StackWalker.getInstance();
    Optional<StackTraceElement> stackTraceElement = walker.walk(frames -> frames
            .findFirst()
            .map(StackWalker.StackFrame::toStackTraceElement));
    
    if (stackTraceElement.isPresent()) {
        // from here you can construct the method being called
        // the same way as you would with the other methods mentioned
    }
}

The advantage of this method is that each StackTraceElement is fetched lazily so you don't actually construct the full stack trace before checking the first method.