dynamically load implementation of interface in Java

Question

I'm looking for functionality in Java similar to the .NET Managed Extensibility Framework (http://mef.codeplex.com/). For those who don't know MEF, I want something like this:

Given an interface

public interface IFoo {
 ...
}

Dynamically load an implementation of an interface by looking in loaded jars.

IFoo foo = loadClassThatImplementsInterface<IFoo>();

The point is that the programmer does not know the name of the implementation at code time, but provides in code an extentsion point.

Is this not possible in Java at all? I found some Google hits stating that it is not possible, but this seems a bit... eh?

There are plenty of examples of using a class loader when the fully qualified name of the implementation is know at compile time. That is not what I want.

Alois Cochard · Accepted Answer · 2010-10-18 08:50:43Z

5

In 'pure' Java you can use ServiceLoader: http://download.oracle.com/javase/6/docs/api/java/util/ServiceLoader.html

You simply provide meta-data in your extension jar, that's smart and extensible easily.

Or look for a DI framework like Guice or Spring...

answered Oct 18, 2010 at 8:50

Alois Cochard

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5 Comments

Pimin Konstantin Kefaloukos Over a year ago

For this project I don't want to use a DI framework, so I'll look into ServiceLoader, thx

Alois Cochard Over a year ago

Ok, don't forget to accept answer if it's what you was looking for ;-) thx

Pimin Konstantin Kefaloukos Over a year ago

Found this after knowing what to look for: java.dzone.com/news/simple-dependency-injection-wi

Pimin Konstantin Kefaloukos Over a year ago

So it's not quite MEF like, as we have to do more than include a jar file in the classpath... so it still sucks a bit.

Alois Cochard Over a year ago

Thanks for link, nice tuto ! yes you must add some code... Unfortunately not full automatic :-( perhaps in some future.

Christoffer Hammarström · Accepted Answer · 2010-10-18 08:51:01Z

0

It's quite possible, with a loadClassThatImplementsInterface(IFoo.class).

answered Oct 18, 2010 at 8:51

Christoffer Hammarström

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