How to cache an answer with jersey?

Question

I am trying to develop a soothing API using Jersey. I have a GET API for a specific receive operation that GET is receiving at the same time from the same client. Is it possible to cache the response? Any pointers are appreciated.

thanks

Answer 1

You can use CacheControl, eTag - follow the sample code below

// In your jersey method final EntityTag eTag = new EntityTag(resource.getId() + "_" + resource.getLastModified().getTime()); final CacheControl cacheControl = new CacheControl(); cacheControl.setMaxAge(-1); ResponseBuilder builder = request.evaluatePreconditions( resource.getLastModified(), eTag); // the resoruce information was modified, return it if (builder == null) { builder = Response.ok(resource); } // the resource information was not modified, return a 304 return builder.cacheControl(cacheControl).lastModified( resource.getLastModified()).tag(eTag).build(); 

Replace resource instance.

Answer 2

Summary of solutions:

• Request as a method parameter

  Interface:

   @Path("myentity") public interface MyEntityResource @GET @Produces(MediaType.APPLICATION_JSON) public Response getMyEntity(@Context final Request request); } 

  Implementation:

   public class MyEntityResourceImpl implements MyEntityResource @Override public Response getMyEntity(final Request request) { final MyEntity myEntity = ... // load entity final String eTagValue = ... // calclutate value of ETag final EntityTag eTag = new EntityTag(eTagValue); ResponseBuilder responseBuilder = request.evaluatePreconditions(eTag); if (responseBuilder == null) { return Response.ok(user).tag(eTag).build(); } return responseBuilder.build(); } } 

  Disadvantages:

  • The implementation detail of Request revealed

  • Reponse return Reponse is common

  • Missing return type grammar in WADL

  • client proxy with unnecessary Request parameter

• Request as an instance variable

  Interface:

   @Path("myentity") public interface MyEntityResource @GET @Produces(MediaType.APPLICATION_JSON) public Response getMyEntity(); } 

  Implementation:

   public class MyEntityResourceImpl implements MyEntityResource @Context private Request request @Override public Response getMyEntity() { final MyEntity myEntity = ... // load entity final String eTagValue = ... // calclutate value of ETag final EntityTag eTag = new EntityTag(eTagValue); ResponseBuilder responseBuilder = request.evaluatePreconditions(eTag); if (responseBuilder == null) { return Response.ok(user).tag(eTag).build(); } return responseBuilder.build(); } } 

  Disadvantages:

  • Reponse return Reponse is common

  • Missing return type grammar in WADL

  • dependency injection with @Context is complicated, see stack overflow.site/questions/791826 / ...

• ShallowEtagHeaderFilter as a web filter

  web.xml:

   <filter> <filter-name>etagFilter</filter-name> <filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class> </filter> <filter-mapping> <filter-name>etagFilter</filter-name> <url-pattern>/api/*</url-pattern> </filter-mapping> 

  Interface:

   @Path("myentity") public interface MyEntityResource @GET @Produces(MediaType.APPLICATION_JSON) public MyEntity getMyEntity(); } 

  Implementation:

   public class MyEntityResourceImpl implements MyEntityResource @Override public MyEntity getMyEntity() { final MyEntity myEntity = ... // load entity return myEntity; } } 

  Disadvantages:

  • Poor server performance, see JavaDoc

  • only works with uncommitted response

  • support weak ETag

• Custom WriterInterceptor as a JAX-RS Interceptor

  interceptor:

   public class CustomInterceptor implements WriterInterceptor { @Context private Request request; @Override public void aroundWriteTo(WriterInterceptorContext context) throws IOException, WebApplicationException { OutputStream old = context.getOutputStream(); ByteArrayOutputStream buffer = new ByteArrayOutputStream(); try { context.setOutputStream(buffer); context.proceed(); byte[] entity = buffer.toByteArray(); String etag = ... // calclutate value of ETag context.getHeaders().putSingle(HttpHeaders.ETAG, etag); ResponseBuilder responseBuilder = request.evaluatePreconditions(eTag); if (responseBuilder == null) { throw new WebApplicationException(responseBuilder.status(Response.Status.NOT_MODIFIED).header(HttpHeaders.ETAG, etag).build()); } old.write(entity); } finally { context.setOutputStream(old); } } } 

  See also: ServerCacheInterceptor (Resteasy)

  Interface:

   @Path("myentity") public interface MyEntityResource @GET @Produces(MediaType.APPLICATION_JSON) public MyEntity getMyEntity(); } 

  Implementation:

   public class MyEntityResourceImpl implements MyEntityResource @Override public MyEntity getMyEntity() { final MyEntity myEntity = ... // load entity return myEntity; } } 

  Disadvantages:

  • There is no predefined interceptor for jersey.

  • Poor server performance

  • support weak ETag

  • Ugly workaround with WebApplicationException

Answer 3

You can use any caching mechanism applicable for standard java along with jersey, for example Ehcache .

You only need to pay attention to make sure that your data in the backend has not changed.

Here is a simple example with Ehcache :

 @GET @Path("{id}") public List<Data> getData(@PathParam("id") Long id) { Element element = CacheManager.getInstance().getCache("test").get(id); if(element == null) { Data value = fetchElementFromBackend(id); CacheManager.getInstance().getCache("test").put(new Element(id, value)); return value; } return element.getObjectValue(); }