Skip to content

Instantly share code, notes, and snippets.

@cchacin
Created May 9, 2014 22:23
Show Gist options
  • Save cchacin/a43cc2b88ccf621e8bbb to your computer and use it in GitHub Desktop.
Save cchacin/a43cc2b88ccf621e8bbb to your computer and use it in GitHub Desktop.
JAX-RS Conditional Cache Headers -> https://devcenter.heroku.com/articles/jax-rs-http-caching
@Path("/books")
public class BookResource {
// less bandwidth
@GET
@Path("/{id}")
public Response getBook(@PathParam("id") long id, @Context Request request){
Book myBook = getBookFromDB(id);
CacheControl cc = new CacheControl();
cc.setMaxAge(86400);
EntityTag etag = new EntityTag(Integer.toString(myBook.hashCode()));
ResponseBuilder builder = request.evaluatePreconditions(etag);
// cached resource did change -> serve updated content
if(builder == null){
builder = Response.ok(myBook);
builder.tag(etag);
}
builder.cacheControl(cc);
return builder.build();
}
@PUT
@Path("/{id}")
@Consumes("application/json")
public Response getBook(@PathParam("id") long id, @Context Request request, Book updatedBook){
Book myBook = getBookFromDB(id);
EntityTag etag = new EntityTag(Integer.toString(myBook.hashCode()));
ResponseBuilder builder = request.evaluatePreconditions(etag);
// client is not up to date (send back 412)
if(builder != null){
return builder.build();
}
updateBookInDB(updatedBook);
builder = Response.noContent();
return builder.build();
}
}
@ingoclaro
Copy link

Overall the idea is good.

Usually on the get side the client wont send an etag. That technique works well for websites as the browser takes care of those things automatically and has it's own cache of the web pages, the same does not happen with an API and their clients.

The put part could have a similar issue if we don't instruct the client to save the etag from the GET response header.

@cchacin
Copy link
Author

cchacin commented Aug 16, 2014

Obviously, if we are using cURL or we don't instruct to our client to use this advantages nothing happen, but is not a issue, simply we aren't using an available feature :)

In JAX-RS 2.0 we can use something like this:

@Provider
public class ConditionalGetFilter implements ClientRequestFilter {

   public void filter(ClientRequestContext req) {
      if ("GET".equals(req.getMethod())) {
         CacheEntry entry = cache.getEntry(req.getURI());
         if (entry != null) {
            req.getHeaders().putSingle("ETag", entry.hashCode());
         }
      }
   }
}

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment