A Guice utility for binding to legacy classes

You're going along, happily Guicing your world, when you run into a snag. There's a class Legacy that you'd like to be able to bind things to, but you can't edit the source to add the @Inject annotations. It looks like this:

public class Legacy implements SomeInterface {
 public Legacy(LegacyDependency dep, String str) {
   ...
 }
 public void initialize(LegacyConfig cfg) {
   ...
 }
 ...
}

And you wish it looked like this:

public class Legacy implements SomeInterface {
 @Inject public Legacy(LegacyDependency dep,
                       @MyAnnotation String str) {
   ...
 }
 @Inject public void initialize(LegacyConfig cfg) {
   ...
 }
 ...
}

You're used to Guice by now, so right away you think, "No problem, I'll use a Provider!"

public class LegacyProvider
     implements Provider<Legacy> {

 public Legacy get() {
   Legacy result = new Legacy(dep, str);
   result.initialize(cfg);
   return result;
 }

 @Inject LegacyDependency dep;
 @Inject @MyAnnotation String str;
 @Inject LegacyConfig cfg;
}

...

 protected void configure() {
   bind(SomeInterface.class)
     .toProvider(LegacyProvider.class)
     .in(WEB_APPLICATION_SCOPE);
 }

So you've written a Provider<Legacy>, and it works. But now you have this extra class to maintain. It's not complicated, in fact it's quite trivial. It seems like something you shouldn't have had to write. You'd rather write something like this:

 bind(SomeInterface.class)
   .toProvider(

     fromConstructor(Legacy.class,
       Key.get(LegacyDependency.class),
       Key.get(String.class, MyAnnotation.class))

     .injecting("initialize",
       Key.get(LegacyConfig.class))

     )

   .in(WEB_APPLICATION_SCOPE);

If this looks like something you want, check out my implementation in the DWR-Guice integration sources. The javadocs are there, too, but they aren't complete. It doesn't have anything to do with DWR, but it seems like a nice convenience to provide.

There are also several flavors of factory-method-based providers, so you don't have to write a special provider just to call a factory method.

I wrote it because even though I've been able to jettison a lot of baggage as I migrate from Spring to Guice, there are still Spring things I want to keep using, like JavaMailSender. I don't want to have to write provider implementations for each one.