JAX-RS provides the @Context annotation to inject a variety of resources in your RESTful services. Some of the most commonly injected components are HTTP headers, HTTP URI related information. Here is a complete list (in no specific order)

• HTTP headers
• HTTP URI details
• Security Context
• Resource Context
• Request
• Configuration
• Application
• Providers

Lets look at these one by one with the help of examples

HTTP headers

Although HTTP headers can be injected using the @HeaderParam annotation, JAX-RS also provides the facility of injecting an instance of the HttpHeaders interface (as an instance variable or method parameter). This is useful when you want to iterate over all possible headers rather than injecting a specific header value by name

@Path("testinject")
public class InjectURIDetails{
    //localhost:8080/<root-context>/testinject/httpheaders
    @GET
    @Path("httpheaders")
    public void test(@Context HttpHeaders headers){
        System.out.println("ALL headers -- "+ headers.getRequestHeaders().toString());
        System.out.println("'Accept' header -- "+ headers.getHeaderString("Accept"));
        System.out.println("'TestCookie' value -- "+ headers.getCookies().get("TestCookie").getValue());
    }
}

UriInfo is another interface whose instance can be injected by JAX-RS (as an instance variable or method parameter). Use this instance to fetch additional details related to the request URI and its parameters (query, path)

@Path("testinject")
public class InjectURIDetails{
  //localhost:8080/<root-context>/testinject/uriinfo
  @GET
  @Path("uriinfo")
  public void test(@Context UriInfo uriDetails){
      System.out.println("ALL query parameters -- "+ uriDetails.getQueryParameters().toString());
      System.out.println("'id' query parameter -- "+ uriDetails.getQueryParameters.get("id"));
      System.out.println("Complete URI -- "+ uriDetails.getRequestUri());
  }
}

An instance of the Providers interface can be injected using @Context. One needs to be aware of the fact that this is only valid within an existing provider. A Providers instance enables the current Provider to search for other registered providers in the current JAX-RS container.

Note: Please do not get confused between Provider and Providers.

Provider

• A JAX-RS Provider is a is generic term for any class which supplements/extends the JAX-RS features by implementing standard interfaces exposed by the JAX-RS specification
• It is annotated using the @Provider annotation for automatic discovery by the run time
• Examples of JAX-RS providers are – Message Body Reader, Message Body Writer, Exception Mapper and Context Providers.

Providers

Refers to the (injectable) javax.ws.rs.ext.Providers interface which was discussed in this sub section

Security Context

Inject an instance of the javax.ws.rs.core.SecurityContext interface (as an instance variable or method parameter) if you want to gain more insight into identity of the entity invoking your RESTful service. This interface exposes the following information

• Instance of java.security.Principal representing the caller
• Whether or not the user if a part of a specific role
• Which authentication scheme is being used (BASIC/FORM/DIGEST/CERT)
• Whether or not the request invoked over HTTPS

@Path("testinject")
public class InjectSecurityContext{
  //localhost:8080/<root-context>/testinject/securitycontext
  @GET
  @Path("securitycontext")
  public void test(@Context SecurityContext secContext){
      System.out.println("Caller -- "+ secContext.getUserPrincipal()getName());
      System.out.println("Authentication Scheme -- "+ secContext.getAuthenticationScheme());
      System.out.println("Over HTTPS ? -- "+ secContext.isSecure());
      System.out.println("Belongs to 'admin' role? -- "+ secContext.isUserInRole("admin");
  }
}

Until then.. Cheers!