Obtain HTTP headers using HttpHeaders objects

Use Java API for RESTful Web Services (JAX-RS), we can use the HttpHeaders object to access request headers.

By using an injected HttpHeaders object with the JAX-RS runtime environment, the HTTP request headers information is known and available for modification. The @javax.ws.rs.core.Context annotation indicates that a context object is injected. The javax.ws.rs.core.HttpHeaders interface is the interface of the object to inject.

Tasks

1. Determine if your method signature can be modified. If we have created a JAX-RS specific resource method, we can usually modify the resource method signature and add parameters easily because the method does not have constraints on the method signature. However, if the JAX-RS resource method was developed by re-using code and adapting existing classes and methods to add JAX-RS functionality, there might be constraints on the method signature by previously existing code that calls the method. In this case, we might not be able to modify the method signature.

2. If a resource method signature can be modified, add a javax.ws.rs.core.HttpHeaders parameter that is annotated with the @javax.ws.rs.core.Context annotation to the method. When the resource method is invoked, the JAX-RS runtime environment passes an object that implements the HttpHeaders object; for example:

   @Path("/contextexample")
   public class RootResource {
      @GET
      public String getResource(@Context HttpHeaders httpHeaders) {
        /* This calls a method on httpHeaders. */
        return "The client sent a header value of " + headers.getRequestHeaders().getFirst("CustomHeader") + " for CustomHeader";
      }
   }
   

3. If a resource method signature cannot be modified and the class is a root resource, add a javax.ws.rs.core.HttpHeaders field that is annotated with the @javax.ws.rs.core.Context annotation to the class. When the resource is instantiated for a request, an object that implements HttpHeaders is injected; for example:

   @Path("/contextexample")
   public class RootResource {
   
      @Context
       HttpHeaders httpHeaders;
   
      @GET
      public String getResource() {
        /* This calls a method on httpHeaders. */
        return "The client sent a header value of " + headers.getRequestHeaders().getFirst("CustomHeader") + " for CustomHeader";
      }
   }
   

The resource method uses information from the HTTP headers sent in the request to determine an appropriate response.

Example

The following example illustrates a resource that returns a different greeting depending on the setting of the Accept-Language header.

In the following code snippet, the @Context HttpHeaders parameter is added to the method signature. Notice that the @Context annotation and the type declaration are in the parameters list of the getGreeting method.

import java.util.List; 
import java.util.Locale; 
  
import javax.ws.rs.GET; 
import javax.ws.rs.Path; 
import javax.ws.rs.Produces; 
import javax.ws.rs.core.Context; 
import javax.ws.rs.core.HttpHeaders; 
import javax.ws.rs.core.MediaType; 
  
@Path("/contexttest") 
public class HelloWorldInMyLanguage { 

    /**
     *   @return Return the string in the preferred language.
     */
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String getGreeting(@Context HttpHeaders httpHeaders) {
        List<Locale> locales = httpHeaders.getAcceptableLanguages();

        if (locales.size() == 0) {
            return "Hello!";
        }

        Locale locale = locales.get(0);
        if (locale.equals(Locale.FRENCH)) {
            return "Bonjour!";
        } else if (locale.equals(Locale.GERMAN)) {
            return "Guten Tag!";
        } else {
            return "Hello!";
        }
    }
} 

Alternatively, we can choose to declare the @Context HttpHeaders httpHeaders property as a field in the class; for example:

import java.util.List; 
import java.util.Locale; 
  
import javax.ws.rs.GET; 
import javax.ws.rs.Path; 
import javax.ws.rs.Produces; 
import javax.ws.rs.core.Context; 
import javax.ws.rs.core.HttpHeaders; 
import javax.ws.rs.core.MediaType; 
  
@Path("/contexttest") 
public class HelloWorldInMyLanguage { 

    @Context
    HttpHeaders httpHeaders;

    /**
     * @return Return the string in the preferred language.
     */
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String getGreeting() {
        List<Locale> locales = httpHeaders.getAcceptableLanguages();

        if (locales.size() == 0) {
            return "Hello!";
        }

        Locale locale = locales.get(0);
        if (locale.equals(Locale.FRENCH)) {
            return "Bonjour!";
        } else if (locale.equals(Locale.GERMAN)) {
            return "Guten Tag!";
        } else {
            return "Hello!";
        }
    }
}

Use JAX-RS context objects to obtain more information about requests

Obtain information about URIs using UriInfo objects

Evaluating request preconditions using Request objects

Determining security information using SecurityContext objects

Web services specifications and APIs