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POHow does caching work in JAX-RS?
 

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  1. POHow does caching work in JAX-RS?
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    <p>Suppose I have the following web service call using <code>@GET</code> method:</p> <pre><code>@GET @Path(value = "/user/{id}") @Produces(MediaType.APPLICATION_JSON) public Response getUserCache(@PathParam("id") String id, @Context HttpHeaders headers) throws Exception { HashMap&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;(); map.put("id", id); SqlSession session = ConnectionFactory.getSqlSessionFactory().openSession(); Cre8Mapper mapper = session.getMapper(Cre8Mapper.class); // slow it down 5 seconds Thread.sleep(5000); // get data from database User user = mapper.getUser(map); if (user == null) { return Response.ok().status(Status.NOT_FOUND).build(); } else { CacheControl cc = new CacheControl(); // save data for 60 seconds cc.setMaxAge(60); cc.setPrivate(true); return Response.ok(gson.toJson(user)).cacheControl(cc).status(Status.OK).build(); } } </code></pre> <p>To experiment, I slow down the current thread 5 seconds before fetching data from my database.<br> When I call my web service using <a href="https://addons.mozilla.org/en-us/firefox/addon/poster/" rel="noreferrer">Firefox Poster</a>, within 60 seconds it seemed much faster on the 2nd, 3rd calls and so forth, until it passed 60 seconds.<br> However, when I paste the URI to a browser (Chrome), it seemed to slow down 5s everytime. And I'm really confused about how caching is actually done with this technique. Here are my questions: </p> <ol> <li>Does POSTER actually look at the header <code>max-age</code> and decide when to fetch the data? </li> <li>In client side (web, android....), when accessing my web service do I need to check the header and then perform caching manually or the browser already cached the data itself? </li> <li>Is there a way to avoid fetching data from the database every time? I guess I would have to store my data in memory somehow, but could it potentially run out of memory? </li> <li><p>In this tutorial <a href="https://devcenter.heroku.com/articles/jax-rs-http-caching" rel="noreferrer">JAX-RS caching tutorial</a>: How does caching actually work? The first line always fetch the data from the database:</p> <p>Book myBook = getBookFromDB(id);</p></li> </ol> <p>So how it is considered cached? Unless the code doesn't execute in top/down order.</p> <pre><code> @Path("/book/{id}") @GET 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 -&gt; serve updated content if (builder == null){ builder = Response.ok(myBook); builder.tag(etag); } builder.cacheControl(cc); return builder.build(); } </code></pre>
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    1. COSide note, not answering the question: instead of `86400` you can use `TimeUnit.DAYS.toSeconds(1)`. Much easier on the eye and no decoding effort needed ;)
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    2. CO@fge: Thanks ;)
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    3. COSimilarly, you can use `TimeUnit.SECONDS.sleep(5)`, by the way
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