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I am using [[Jersey]] for a long time to implement [[REST]] services and [[I]] am relatively happy [[Jersey]] user. One thing that is problematic is the fact that [[I]] am using [[Jersey]] as a standalone application (without any J2EE container) and finding tutorials how to do it isn't always easy. For example how to use [[Component Injection]] with such standalone [[Jersey]] was a mystery for me for a long time...

== Injection ==

Of course, the trivial things are easy. One can use the '''javax.inject''' annotations to identify the injection slots:

<source lang="java">
@Path("/timing/") @Singleton
public final class TimingResource {
    @Inject
    private Storage storage;
    @Inject
    private ContactsResource contacts;
}
</source>

That is one side of the story. The other side requires one to register classes implementing these components into the system when configuring the server:

<source lang="java">
static HttpServer createServer(URI u, File dir) {
   ResourceConfig rc = new ResourceConfig(
       TimingResource.class, ContactsResource.class, Storage.class, Main.class
   );
   HttpServer server = GrizzlyHttpServerFactory.createHttpServer(u, rc);
}
</source>

Such solution works, but it has one problem: how can the instances be configured? The system just calls their default (no argument) constructor and for example the '''Storage''' class would benefit from actually knowing the location where to store its data. So far I was solving that with a system property: Reading '''System.getProperty("storage.dir")''' inside the default constructor. That is of course quite hacky - I knew there had to be a better way, but I never invested enough time to find it out. Just today...

== Your Own Binder ==

The solution is simple. One can register own '''AbstractBinder''':

<source lang="java">
ResourceConfig rc = new ResourceConfig(
    TimingResource.class, ContactsResource.class, Main.class
);
final Storage storage = dir == null ? Storage.empty() : Storage.forDirectory(dir);
rc.registerInstances(new AbstractBinder() {
    @Override
    protected void configure() {
        bind(storage).to(Storage.class);
    }
});
HttpServer server = GrizzlyHttpServerFactory.createHttpServer(u, rc);
</source> 

Now it is possible to properly prepare and configure the appropriate instance of '''Storage''' and then just '''bind''' it to '''Storage.class''' when the [[Injection]] is about to happen. There is just a single downside: this is a [[Jersey]] specific solution - it uses ''org.glassfish.hk2.utilities.binding.AbstractBinder'' - but yeah, great that it works and the non ''JAX-RS'' standardized code is anyway located just in the '''main''' method initialization.

== The Real Example ==

Here is [https://github.com/jtulach/timing/commit/e5be764bb61c1c251d3d795eb517f559f25fddfc the diff] that [[I]] applied to my [https://github.com/jtulach/timing real project] to enable the use of [[injection]]. And here you can find the change that allows me to pre-configure the instance of '''Storage''' when initializing the server: [https://github.com/jtulach/timing/commit/9e1e7398f9c26b9ca3245e50a09bf8427ccf43de the diff].

== The Best Tutorial ==

Of course, all of this is already explained in an [https://jersey.java.net/documentation/latest/ioc.html existing tutorial] - it is just not that easy to find it. It really helps if a guy who wrote significant part of [[Jersey]] is your co-worker, sitting 2m away from you...

Thanks Jakub!

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