JAX-RS - Interceptors

A JAX-RS interceptor is used to manipulate the message body (entity), by intercepting input/output streams.

To add interceptors, we need to implement ReaderInterceptor and/or WriterInterceptor, they are individually used for request and response respectively.

For automatic discovery, we should use @Provider annotation on the interceptors.

Let's see a quick example how to use interceptors in JAX-RS

Example

Implementing Filter

@Provider
public class MyInterceptor implements WriterInterceptor, ReaderInterceptor {

    @Override
    public Object aroundReadFrom(ReaderInterceptorContext context)
            throws IOException, WebApplicationException {
        System.out.println("-- in MyInterceptor#aroundReadFrom() --");
        System.out.println("request message body:");
        InputStream is = context.getInputStream();
        String body = new Scanner(is, "UTF-8").useDelimiter("\\A").next();
        System.out.println(body);
        context.setInputStream(new ByteArrayInputStream(
                (body+"\nMy appended message in request body.\n").getBytes()));
        Object result = context.proceed();
        return result;
    }

    @Override
    public void aroundWriteTo(WriterInterceptorContext context)
            throws IOException, WebApplicationException {
        System.out.println("-- in MyInterceptor#aroundWriteTo() --");
        OutputStream os = context.getOutputStream();
        os.write("My output message.\n".getBytes());
        context.proceed();
    }
}

A JAX-RS resource

@Path("/")
public class MyResource {

    @POST
    @Path("{path:.*}")
    public String getResponse(@PathParam("path") String path, String entity) {
        System.out.println("-- In the resource method, getResponse() --");
        System.out.println("request message body: "+entity);
        return "dummy-response for " + path;
    }
}

mvn tomcat7:run-war

The Client

public class MyClient {
    public static void main(String[] args) {
        Client client = ClientBuilder.newClient();
        WebTarget target = client.target("http://localhost:8080/app");
        String response = target.request().post(Entity.text("my test request body"), String.class);
        System.out.println(response);
    }
}

Output

My output message.
dummy-response for app

Output On Server console

-- in MyInterceptor#aroundReadFrom() --
request message body:
my test request body
-- In the resource method, getResponse() --
request message body: my test request body
My appended message in request body.

-- in MyInterceptor#aroundWriteTo() --

Other Features of Interceptors

Similar to Filters, we can do the followings with Interceptor:

• Name Binding.
• Dynamic Binding.
• Priories.

Overall Execution Order

Following is the overall order of filters and interceptors on the server side:

Client → The Server receives the request → Request Filters → 
Reader Interceptors → MessageBodyReader → The Resource method Invocation → 
Response Filters → Writer Interceptors → MessageBodyWriter → 
Server dispatches the response → Client

Example Project

Dependencies and Technologies Used:

• jersey-server 2.25.1: Jersey core server implementation.
• jersey-container-servlet 2.25.1: Jersey core Servlet 3.x implementation.
• JDK 1.8
• Maven 3.3.9