Filters and Interceptors - RESTful Java with JAX-RS 2.0 - page 176

Generally, you use these types of filters to decorate the response by adding or modifying re-
sponse headers. One example is if you wanted to set a default Cache-Control header for
each response to a GET request. Here's what it might look like:

import import javax.ws.rs.container.ContainerResponseFilter javax.ws.rs.container.ContainerResponseFilter ;

import import javax.ws.rs.container.ContainerRequestContext javax.ws.rs.container.ContainerRequestContext ;

import import javax.ws.rs.container.ContainerResponseContext javax.ws.rs.container.ContainerResponseContext ;

import import javax.ws.rs.core.CacheControl javax.ws.rs.core.CacheControl ;

@Provider
public public class class CacheControlFilter CacheControlFilter implements implements ContainerResponseFilter {

public public void void filter ( ContainerRequestContext req , ContainerResponseContext res )

throws

throws IOException

{

iif ( req . getMethod (). equals ( "GET" )) {
CacheControl cc = new

new CacheControl ();

cc . setMaxAge ( 100 );
req . getHeaders (). add ( "Cache-Control" , cc );

}

}

}

The ContainerResponseFilter.filter() method has two parameters. The Container-
RequestContext parameter gives you access to information about the request. Here we're
checking to see if the request was a GET. The ContainerResponseContext parameter al-
lows you to view, add, and modify the response before it is marshalled and sent back to the
client. In the example, we use the ContainerResponseContext to set a Cache-Control re-
sponse header.

Reader and Writer Interceptors

While filters modify request or response headers, reader and writer interceptors deal with
message bodies. They work in conjunction with a MessageBodyReader or Mes-
sageBodyWriter and are usable on both the client and server. Reader interceptors implement
the ReaderInterceptor interface. Writer interceptors implement the WriterInterceptor
interface.

package package javax . ws . rs . ext ;

public public interface interface ReaderInterceptor ReaderInterceptor {

public public Object aroundReadFrom ( ReaderInterceptorContext context )

throws throws java . io . IOException , javax . ws . rs . WebApplicationException ;

}