Writing a java annotation for timing method call

Question

I want to write a java annotation which times the method call. something like this:

@TimeIt
public int someMethod() { ... }

and when this method is invoked, it should output on console how long this method took

I know how to do it in python, this is what I want it to do:

from time import time, sleep

def time_it(func):
    def wrapper(*args, **kwargs):
        start = time()
        func(*args, **kwargs)
        stop = time()
        print "The function", func.__name__, " took %.3f" % (stop - start)
    wrapper.__name__ = func.__name__
    return wrapper

@time_it
def print_something(*args, **kwargs):
    print "before sleeping"
    print args, kwargs
    sleep(3) # wait 3 seconds
    print "after sleeping"

print_something(1, 2, 3, a="what is this?")

So my questions are? Where do I find some documentation to write something like this, I tried apt documentation, had no luck with it. can someone help with writing something like this?

Answer 1

It isn't nearly as easy in Java. The basic idea would be this:

1. Create annotation that says "time this method"
2. Create a java agent that uses byte code transformation to: a. Find methods with the annotation b. Add timing code to them
3. Set the javaagent option when you run java to use your new agent

This article would get you started: http://today.java.net/pub/a/today/2008/04/24/add-logging-at-class-load-time-with-instrumentation.html .

You might also be able to use BTrace to make this even easier: http://kenai.com/projects/btrace/pages/Home

Answer 2

Despite all the nay-sayers, you can do this. Java annotations cannot change the source or class files they operate on, so your options are:

1) Use a super class. The annotation processor can generate a super-class that times an abstract method. Your actual class implements this method. The downsides is that the method you want to time has to be renamed so that the super-class can provide an implementation. The result might look like this

@BenchmarkMe( extend="MySuperClass" )
public class MyClass extends BenchmarkMyClass {
    public void normalMethod() { ... }
    public void bench_myMethod() { ... }
}  

and the annotation process would generate:

public class BenchmarkMyClass extends MySuperClass {
    public abstract void bench_myMethod();
    public void myMethod() {
       benchmarkStart();
       try {
          bench_myMethod();
       } finally { benchmarkStop(); }
    }
}

By using a naming convention to indicate which methods should be timed as the prefix "bench_" was used in my example.

2) Use a ClassFileTranformer as well as an Annotation The approach would be to create a runtime annotation that can be used to mark the methods you are interested in timing. At runtime a ClassFileTransformer is specified on the command line and it transforms the byte code to insert the timing code.

Unless you like working with byte code, using AOP is the better bet, but it IS possible.

Answer 3

I wondered the same thing several time and ended by writting the following start:

The annotation:

package main;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Clocking {

}

An object's interface:

package main;

public interface Examples {
    @Clocking
    void thisIsAMethod();

    void thisIsAnotherMethod(String something);

    @Clocking
    void thisIsALongRunningMethod();
}

An invocation handler:

package main;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.time.Duration;
import java.time.Instant;

public class ExamplesInvocationHandler implements InvocationHandler {
    // ******************************
    // Fields
    // ******************************
    private Examples examples = new ExamplesImpl();

    // ******************************
    // Public methods
    // ******************************
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        // If the annotation is not present, just redirect the method call to its origin...
        if(!method.isAnnotationPresent(Clocking.class)) {
            return method.invoke(examples, args);
        }

        // ... otherwise log the execution time of it.
        Instant start = Instant.now();
        Object returnObj = method.invoke(examples, args);
        Instant end = Instant.now();

        // TODO: This is for demonstration purpose only and should use the application's logging system.
        System.out.println("Method " + method.getName() + " executed in " + Duration.between(end, start) + ".");

        return returnObj;
    }

    // ******************************
    // Inner classes
    // ******************************
    private static class ExamplesImpl implements Examples {
        @Override
        public void thisIsAMethod() {
            System.out.println("thisIsAMethod called!");
        }

        @Override
        public void thisIsAnotherMethod(String something) {
            System.out.println("thisIsAnotherMethod called!");
        }

        @Override
        public void thisIsALongRunningMethod() {
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            System.out.println("thisIsALongRunningMethod called!");
        }
    }
}

An finally an entry point to test this:

package main;
import java.lang.reflect.Proxy;

public class Main {
    public static void main(String[] args) {
        Examples examples = (Examples) Proxy.newProxyInstance(Examples.class.getClassLoader(), new Class[]{Examples.class}, new ExamplesInvocationHandler());

        examples.thisIsAMethod();
        examples.thisIsAnotherMethod("");
        examples.thisIsALongRunningMethod();
    }
}

This needs an improvement, since it requires Proxy to instantiate our object and so you can't really use it for "generic already written" code. But it might leads you to something more complete.