Question

Disclaimer: I have 10 years’ experience programming, but 8 of which is in PHP (loosely typed) — I have been using Java now for 4 days 🙂

In java, I need to get the value of an annotation for a method in the call stack. As far as I can tell, I do this with the Method object. From the call stack, I have retrieved the names of the class and method (strings). This is the (abbreviated) code that I am using…

Calling Method:

public class myClass
{
   @Path( "some/path/value" )
   public void myMethod( String someArg ) { ... }
}

Retrieval Code:

StackTraceElement[] trace = Thread.currentThread().getStackTrace();
String callingMethodName = trace[depth].getMethodName();
String callingClassName = trace[depth].getClassName();

Class[] signature = new Class[1];
signature[0] = String.class;

Class callingClass = Class.forName( callingClassName );
Method callingMethod = callingClass.getMethod( callingMethodName, signature );
Path annotation = callingMethod.getAnnotation( Path.class );

This works like a charm, successfully returning the value of the @Path annotation ("some/path/value")

However, if you notice, I had to supply a signature of the method I was looking for. As you can see in the class code, there is only 1 method with that name, so, theoretically, the signature of the method should be irrelevant, right? As far as I can tell from various docs/blogs/examples, I should be able to call getMethod( ) with either no 2nd argument, or with null for the 2nd argument, but if I use the following:

Class callingClass = Class.forName( callingClassName );
Method callingMethod = callingClass.getMethod( callingMethodName );

Or even:

Class callingClass = Class.forName( callingClassName );
Method callingMethod = callingClass.getMethod( callingMethodName, null );

I get a NoSuchMethodException. Am I doing something wrong here? Should I be taking a different approach altogether?

In this particular situation, the calling class/method never uses polymorphism so there is only ever 1 signature. However, said signature is not known (unless that can also be determined by data available/derivable from Thread.currentThread( )), so I need a way to get a Method object without knowing the signature.

Answer 1

No. The signature matters. If you don’t know the exact signature, but know the name, get all the methods and iterate over them until you get a hit:

Method method = null;
for (Method m : c.getDeclaredMethods()) {
    if (m.getName().equals(callingMethodName)) {
        method = m;
        break;
    }
}
// variable "method" is the first that matched name, or null if not found

Also, since java 1.5, Class.getMethod(String, Class...) is a varargs method, so you don’t need the java cruft that both the question and other answer has, ie:

This works, but avoid this crap (the old, hard way):

Class[] signature = new Class[1];
signature[0] = String.class;
Method callingMethod = callingClass.getMethod( callingMethodName, signature);

Prefer this (new way):

Method callingMethod = callingClass.getMethod( callingMethodName, String.class);