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JAX-RS: What Is @Context?

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JAX-RS: What Is @Context?

When using JAX-RS, we often need to make use of the @Context annotation. But what exactly does it do? And what separates it from @Inject.

· Java Zone ·
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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.

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Topics:
java ee ,java ,jax-rs ,annotation ,context ,tutorial

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