reflection - Get callers method (java.lang.reflect.Method)

Question

I would like to get the calling method java.lang.reflect.Method. NOT the name of the method.

Here is an example how to get the callers Class.

// find the callers class
Thread t = Thread.getCurrentThread();
Class<?> klass = Class.forName(t.getStackTrace()[2].getClassName());
// do something with the class (like processing its annotations)
... 

It's for testing purpose only!

Answer 1

If it's just for testing, then this may work. It assumes that the class files are accessible via the calling class's ClassLoader and that the class files were compiled with debugging symbols (which I hope they are for testing!). This code relies on the ASM bytecode library.

public static Method getMethod(final StackTraceElement stackTraceElement) throws Exception {
    final String stackTraceClassName = stackTraceElement.getClassName();
    final String stackTraceMethodName = stackTraceElement.getMethodName();
    final int stackTraceLineNumber = stackTraceElement.getLineNumber();
    Class<?> stackTraceClass = Class.forName(stackTraceClassName);

    // I am only using AtomicReference as a container to dump a String into, feel free to ignore it for now
    final AtomicReference<String> methodDescriptorReference = new AtomicReference<String>();

    String classFileResourceName = "/" + stackTraceClassName.replaceAll("\.", "/") + ".class";
    InputStream classFileStream = stackTraceClass.getResourceAsStream(classFileResourceName);

    if (classFileStream == null) {
        throw new RuntimeException("Could not acquire the class file containing for the calling class");
    }

    try {
        ClassReader classReader = new ClassReader(classFileStream);
        classReader.accept(
                new EmptyVisitor() {
                    @Override
                    public MethodVisitor visitMethod(int access, final String name, final String desc, String signature, String[] exceptions) {
                        if (!name.equals(stackTraceMethodName)) {
                            return null;
                        }

                        return new EmptyVisitor() {
                            @Override
                            public void visitLineNumber(int line, Label start) {
                                if (line == stackTraceLineNumber) {
                                    methodDescriptorReference.set(desc);
                                }
                            }
                        };
                    }
                },
                0
            );
    } finally {
        classFileStream.close();
    }

    String methodDescriptor = methodDescriptorReference.get();

    if (methodDescriptor == null) {
        throw new RuntimeException("Could not find line " + stackTraceLineNumber);
    }

    for (Method method : stackTraceClass.getMethods()) {
        if (stackTraceMethodName.equals(method.getName()) && methodDescriptor.equals(Type.getMethodDescriptor(method))) {
            return method;
        }
    }

    throw new RuntimeException("Could not find the calling method");
}