Java Top

Get started with Spring 5 and Spring Boot 2, through the Learn Spring course (COVID-pricing ends in January):

>> CHECK OUT THE COURSE

1. Overview

Sometimes we need to know the name of the current Java method being executed.

This quick article presents a couple of simple ways of getting hold of the method name in the current execution stack.

2. Java 9: Stack-Walking API

Java 9 introduced the Stack-Walking API to traverse the JVM stack frames in a lazy and efficient manner. In order to find the currently executing method with this API, we can write a simple test:

public void givenJava9_whenWalkingTheStack_thenFindMethod() {
    StackWalker walker = StackWalker.getInstance();
    Optional<String> methodName = walker.walk(frames -> frames
      .findFirst()
      .map(StackWalker.StackFrame::getMethodName));

    assertTrue(methodName.isPresent());
    assertEquals("givenJava9_whenWalkingTheStack_thenFindMethod", methodName.get());
}

First, we get a StackWalker instance using the getInstance() factory method. Then we use the walk() method to traverse the stack frames from the top to the bottom:

  • The walk() method can convert a stream of stack frames — Stream<StackFrame> — to anything
  • The first element in the given stream is the top frame on the stack
  • The top frame on the stack always represents the currently executing method

Therefore, if we get the first element from the stream, we'll know the currently executing method details. More specifically, we can use StackFrame.getMethodName() to find the method name.

2.1. Advantages

Compared to other approaches (more on them later), the Stack-Walking API has a few advantages:

  • No need to create a dummy anonymous inner class instance — new Object().getClass() {}
  • No need to create a dummy exception — new Throwable()
  • No need to eagerly capture the whole stacktrace, which can be costly

On the contrary, the StackWalker only walks the stack one by one in a lazy fashion. In this case, it only fetches the top frame, as opposed to the stacktrace approach which captures all the frames eagerly.

The bottom line is, use the Stack-Walking API if you're on Java 9+.

3. Using getEnclosingMethod

We can find the name of the method being executed by using the getEnclosingMethod() API:

public void givenObject_whenGetEnclosingMethod_thenFindMethod() {
    String methodName = new Object() {}
      .getClass()
      .getEnclosingMethod()
      .getName();
       
    assertEquals("givenObject_whenGetEnclosingMethod_thenFindMethod",
      methodName);
}

4. Using Throwable Stack Trace

Using a Throwable stack trace gives us stack trace with the method currently being executed:

public void givenThrowable_whenGetStacktrace_thenFindMethod() {
    StackTraceElement[] stackTrace = new Throwable().getStackTrace();
 
    assertEquals(
      "givenThrowable_whenGetStacktrace_thenFindMethod",
      stackTrace[0].getMethodName());
}

5. Using Thread Stack Trace

Also, the stack trace of a current thread (since JDK 1.5) usually includes the name of the method that is being executed:

public void givenCurrentThread_whenGetStackTrace_thenFindMethod() {
    StackTraceElement[] stackTrace = Thread.currentThread()
      .getStackTrace();
 
    assertEquals(
      "givenCurrentThread_whenGetStackTrace_thenFindMethod",
      stackTrace[1].getMethodName()); 
}

However, we need to remember that this solution has one significant drawback. Some virtual machines may skip one or more stack frames. Although this is not common, we should be aware that this can happen.

6. Conclusion

In this tutorial, we have presented some examples of how to get the name of the currently executed method. Examples are based on stack traces and the getEnclosingMethod().

As always, you can check out the examples provided in this article over on GitHub. Also, Java 9 examples are available in our Java 9 GitHub module.

Java bottom

Get started with Spring 5 and Spring Boot 2, through the Learn Spring course (COVID-pricing ends in January):

>> CHECK OUT THE COURSE
4 Comments
Oldest
Newest
Inline Feedbacks
View all comments
Comments are closed on this article!