java - Where do @Context objects come from

Question

I've been searching everywhere, but can't seem to find a clear answer...

What is the mechanism whereby a server (glassfish for my problem) injects actual objets that are annotated with @Context? More specifically, if I wanted to write a class that did something like:

@Path("/")
public class MyResource {
  @GET
  public String doSomething(@Context MyObject obj) {
    // ...
  }
}

then how would I do it? Where is it that the MyObject is instanciated, who does it, and how?

Edit: I've seen stuff like the following:

Using @Context, @Provider and ContextResolver in JAX-RS

http://jersey.576304.n2.nabble.com/ContextResolver-confusion-td5654154.html

However, this doesn't square with what I've seen, e.g. in the constructor of org.neo4j.server.rest.web.RestfulGraphDatabase, which has the following signature:

public RestfulGraphDatabase(
  @Context UriInfo uriInfo,
  @Context Database database,
  @Context InputFormat input,
  @Context OutputFormat output,
  @Context LeaseManager leaseManager )

Answer 1

You can write your own injection provider and plug that into Jersey - look at SingletonTypeInjectableProvider and PerRequestTypeInjectableProvider - extend one of these classes (depending on the lifecycle you want for the injectable object) and register your implementation as a provider in your web app.

For example, something like this:

@Provider
public class MyObjectProvider extends SingletonTypeInjectableProvider<Context, MyObject> {
    public MyObjectProvider() {
        // binds MyObject.class to a single MyObject instance
        // i.e. the instance of MyObject created bellow will be injected if you use
        // @Context MyObject myObject
        super(MyObject.class, new MyObject());
    }
}

To include the provider in your web app you have several options:

1. if your app uses classpath scanning (or package scanning) just make sure the provider is in the right package / on the classpath
2. or you can simply register it using META-INF/services entry (add META-INF/services/com.sun.jersey.spi.inject.InjectableProvider file having the name of your provider class in it's contents)