JAX-RS 2: How to compress response if client accepts gzip; "Accept-Encoding: gzip, deflate, sdch"

AcceptGZIP.java

// Create a WriterInterceptor, 
// see: https://jersey.java.net/documentation/latest/user-guide.html#d0e9728

import ...

@Provider
public class GZIPWriterInterceptor implements WriterInterceptor {
    private final Logger logger = LoggerFactory.getLogger(getClass());
    private HttpHeaders httpHeaders;

    public GZIPWriterInterceptor(@Context @NotNull HttpHeaders httpHeaders) {
        this.httpHeaders = httpHeaders;
    }

    @Override
    public void aroundWriteTo(WriterInterceptorContext context) 
        throws IOException, WebApplicationException {

        MultivaluedMap<String,String> requestHeaders =  httpHeaders.getRequestHeaders();
        List<String> acceptEncoding = MoreObjects.firstNonNull(
                requestHeaders.get(HttpHeaders.ACCEPT_ENCODING), new ArrayList<String>());

        // Compress if client accepts gzip encoding
        for (String s : acceptEncoding) {
            if(s.contains("gzip")) {
                logger.debug("GZIP'ing response");

                MultivaluedMap<String, Object> headers = context.getHeaders();
                headers.add(HttpHeaders.CONTENT_ENCODING, "gzip"); 
                    //com.google.common.net.MediaType.GZIP);

                final OutputStream outputStream = context.getOutputStream();
                context.setOutputStream(new GZIPOutputStream(outputStream));

                break;
            }
        }
        context.proceed();
    }
}

// If we're using the client api, then we need a ReaderInterceptor as well
import ...

public class GZIPReaderInterceptor implements ReaderInterceptor {
    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Override
    public Object aroundReadFrom(ReaderInterceptorContext context) 
        throws IOException, WebApplicationException {

        MultivaluedMap<String,String> headers = context.getHeaders();

        List<String> contentEncoding = MoreObjects.firstNonNull(
                headers.get(HttpHeaders.CONTENT_ENCODING), new ArrayList<String>());

        for (String s : contentEncoding) {
            if(s.contains("gzip")) {
                logger.debug("Decompressing GZIP");

                final InputStream originalInputStream = context.getInputStream();
                context.setInputStream(new GZIPInputStream(originalInputStream));

                break;
            }
        }
        return context.proceed();
    }
}

// Register ReaderInterceptor on client-api
@BeforeClass
public static void startServer() throws Exception {
    // Start the server
    // ... Code ommited for brewety
    
    // Create the client
    Client c = ClientBuilder.newClient();

    // Client interceptor to deflate GZIP'ed content on client side
    c.register(GZIPReaderInterceptor.class);

    target = c.target(server.getURI()).path(JerseyJpaApp.APPLICATION_PATH);
}

// Set header(HttpHeaders.ACCEPT_ENCODING, "gzip") in request
@Test
public void getBookByIsbnShouldReturn_OK() {
    final Response response = target
            .path(BookResource.RESOURCE_PATH)
            .path(ISBN_TRAVELING_TO_INFINITY)
            .request(MediaType.APPLICATION_JSON_TYPE)
            .header(HttpHeaders.ACCEPT_ENCODING, "gzip")
            .get();

    assertEquals(Response.Status.OK.getStatusCode(), response.getStatus());

    List<Object> objects = response.getHeaders().get("Content-Encoding");
    assertNotNull(objects);
    assertThat(objects.toString(), containsString("gzip"));
}

// That's it :-)

// If you're sending request from a browser then
// set "Accept-Encoding: gzip, deflate, sdch" before sending request
// Note: this is the default setting in Chrome (I think)

What about http://www.codingpedia.org/ama/how-to-compress-responses-in-java-rest-api-with-gzip-and-jersey/

Basically same code as found here: https://jersey.java.net/documentation/latest/user-guide.html#d0e9728. We can extend further and combine HttpHeaders.CONTENT_ENCODING with the @compress annotation to compress only when request method is annotated with @compress. In this way we can return compressed content given that the client accepts gzip and response method is annotated with @compress

After the call to proceed(), the GZIP stream must be explicitly closed (at least in Java-SE 1.8), or there will be no output.