Vfrdtyky

Looks like it might be possible after all, by using a proxy to record which method gets called.

https://stackoverflow.com/a/22745127/3478229

In my case I was looking for a way to get rid of this in unit tests:

Point p = getAPoint();

assertEquals(p.getX(), 4, "x");

assertEquals(p.getY(), 6, "x");

As you can see someone is testing Method getAPoint and checks that the coordinates are as expected, but in the description of each assert was copied and is not in sync with what is checked. Better would be to write this only once.

From the ideas by @ddan I built a proxy solution using Mockito:

private<T> void assertPropertyEqual(final T object, final Function<T, ?> getter, final Object expected) {

    final String methodName = getMethodName(object.getClass(), getter);

    assertEquals(getter.apply(object), expected, methodName);

}



@SuppressWarnings("unchecked")

private<T> String getMethodName(final Class<?> clazz, final Function<T, ?> getter) {

    final Method method = new Method[1];

    getter.apply((T)Mockito.mock(clazz, Mockito.withSettings().invocationListeners(methodInvocationReport -> {

        method[0] = ((InvocationOnMock) methodInvocationReport.getInvocation()).getMethod();

    })));

    return method[0].getName();

}

No I can simply use

assertPropertyEqual(p, Point::getX, 4);

assertPropertyEqual(p, Point::getY, 6);

and the description of the assert is guaranteed to be in sync with the code.

Downside:

• Will be slightly slower than above


• Needs Mockito to work


• Hardly useful to anything but the usecase above.

However it does show a way how it could be done.

Though I haven't tried it myself, I think the answer is "no," since a method reference is semantically the same as a lambda.

If you can make the interface Action extend Serializable, then this answer from another question seems to provide a solution (at least on some compilers and runtimes).

We have published the small library de.cronn:reflection-util that can be used to capture a method name.

Example:

class MyClass {



    public void myMethod() {

    }



}



String methodName = ClassUtils.getVoidMethodName(MyClass.class, MyClass::myMethod);

System.out.println(methodName); // prints "myMethod"

Implementation details: A Proxy subclass of MyClass is created with ByteBuddy and a call to the method is captured to retrieve its name.
ClassUtils caches the information such that we do not need to create a new proxy on every invocation.

Please note that this approach doesn’t work with static methods.

There may not be a reliable way, but under some circumstances:

1. your MyClass is not final, and has an accessible constructor (limitation of cglib)


2. your myMethod is not overloaded, and not static

The you can try using cglib to create a proxy of MyClass, then using an MethodInterceptor to report the Method while the method reference is invoked in a following trial run.

Example code:

public static void main(String args) {

    Method m = MethodReferenceUtils.getReferencedMethod(ArrayList.class, ArrayList::contains);

    System.out.println(m);

}

You will see the following output:

public boolean java.util.ArrayList.contains(java.lang.Object)

While:

public class MethodReferenceUtils {



    @FunctionalInterface

    public static interface MethodRefWith1Arg<T, A1> {

        void call(T t, A1 a1);

    }



    public static <T, A1> Method getReferencedMethod(Class<T> clazz, MethodRefWith1Arg<T, A1> methodRef) {

        return findReferencedMethod(clazz, t -> methodRef.call(t, null));

    }



    @SuppressWarnings("unchecked")

    private static <T> Method findReferencedMethod(Class<T> clazz, Consumer<T> invoker) {

        AtomicReference<Method> ref = new AtomicReference<>();

        Enhancer enhancer = new Enhancer();

        enhancer.setSuperclass(clazz);

        enhancer.setCallback(new MethodInterceptor() {

            @Override

            public Object intercept(Object obj, Method method, Object args, MethodProxy proxy) throws Throwable {

                ref.set(method);

                return null;

            }

        });

        try {

            invoker.accept((T) enhancer.create());

        } catch (ClassCastException e) {

            throw new IllegalArgumentException(String.format("Invalid method reference on class [%s]", clazz));

        }



        Method method = ref.get();

        if (method == null) {

            throw new IllegalArgumentException(String.format("Invalid method reference on class [%s]", clazz));

        }



        return method;

    }

}

In the above code, MethodRefWith1Arg is just a syntax sugar for you to reference an non-static method with one arguments. You can create as many as MethodRefWithXArgs for referencing your other methods.

You can add safety-mirror to your classpath and do like this:

Method m1 = Types.createMethod(Thread::isAlive)  // Get final method

Method m2 = Types.createMethod(String::isEmpty); // Get method from final class

Method m3 = Types.createMethod(BufferedReader::readLine); // Get method that throws checked exception

Method m4 = Types.<String, Class>createMethod(getClass()::getDeclaredMethod); //to get vararg method you must specify parameters in generics

Method m5 = Types.<String>createMethod(Class::forName); // to get overloaded method you must specify parameters in generics

Method m6 = Types.createMethod(this::toString); //Works with inherited methods

The library also offers a getName(...) method:

assertEquals("isEmpty", Types.getName(String::isEmpty));

The library is based on Holger's answer: https://stackoverflow.com/a/21879031/6095334

Edit: The library have various shortcomings which I am slowly becoming aware of.
See fx Holger's comment here: How to get the name of the method resulting from a lambda

You can use my library Reflect Without String

Method myMethod = ReflectWithoutString.methodGetter(MyClass.class).getMethod(MyClass::myMethod);

So, I play with this code

import sun.reflect.ConstantPool;



import java.lang.reflect.Method;

import java.util.function.Consumer;



public class Main {

    private Consumer<String> consumer;



    Main() {

        consumer = this::test;

    }



    public void test(String val) {

        System.out.println("val = " + val);

    }



    public void run() throws Exception {

        ConstantPool oa = sun.misc.SharedSecrets.getJavaLangAccess().getConstantPool(consumer.getClass());

        for (int i = 0; i < oa.getSize(); i++) {

            try {

                Object v = oa.getMethodAt(i);

                if (v instanceof Method) {

                    System.out.println("index = " + i + ", method = " + v);

                }

            } catch (Exception e) {

            }

        }

    }



    public static void main(String args) throws Exception {

        new Main().run();

    }

}

output of this code is:

index = 30, method = public void Main.test(java.lang.String)

And as I notice index of referenced method is always 30.
Final code may look like

public Method unreference(Object methodRef) {

        ConstantPool constantPool = sun.misc.SharedSecrets.getJavaLangAccess().getConstantPool(methodRef.getClass());

        try {

            Object method = constantPool.getMethodAt(30);

            if (method instanceof Method) {

                return (Method) method;

            }

        }catch (Exception ignored) {

        }

        throw new IllegalArgumentException("Not a method reference.");

    }

Be careful with this code in production!

Try this

Thread.currentThread().getStackTrace()[2].getMethodName();