JAX-RS: What Is @Context?

The JAX-RS API from the Java EE ecosystem of technologies provides the annotation @Context, to inject 12 object instances related to the context of HTTP requests. It behaves just like the @Inject and @Autowired annotations in Java EE and Spring respectively.

The object instances that it can inject are the following:

• SecurityContext – Security context instance for the current HTTP request
• Request – Used for setting precondition request processing
• Application, Configuration, and Providers -> Provide access to the JAX-RS application, configuration, and providers instances
• ResourceContext – Resource context class instances
• ServletConfig – The ServletConfig instance instance
• ServletContext – The ServletContext instance
• HttpServletRequest – The HttpServletRequest instance for the current request
• HttpServletResponse – The HttpServletResponse instance for the current request
• HttpHeaders – Maintains the HTTP header keys and values
• UriInfo – Query parameters and path variables from the URI called

It is a little confusing to have both an @Inject and @Context when both do the same job of injecting objects, but it is envisioned that future version of Java EE will bring more alignment of annotation use.

Where Is @Context Used?

It can be used to inject any of the above-mentioned instances into an instance field or directly into the resource method as a parameter.

Below is an example of the injecting into a method’s resource method parameter list:

@Path("/")
public class EndpointResource {

@GET
@Produces(MediaType.APPLICATION_JSON)
public Response getHeaders(final @Context HttpHeaders httpHeaders){
    // Code here that uses httpHeaders
    }
}

And here’s an example of injection into an instances field:

@Path("/")
public class EndpointResource {

    private final @Context HttpHeaders httpHeaders;

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public Response getHeaders(){
        // Code here that uses httpHeaders
    }
}

If you want to know more, take a look at this series of articles answering the question What is @Conext in JAX-RS used for?

Code Repository

The source code for this article is in my GitHub repository. Code for all my articles is in the ReadLearnCode Articles repository.