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POUse GZIP, JSON responses and JQuery
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  1. POUse GZIP, JSON responses and JQuery
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    copied!<p>However, I want to compress my responses with GZIP wheren possible. I tried using the <a href="http://www.headfirstlabs.com/books/hfsvlt/" rel="noreferrer">Compression filter code</a> available for free download in the headfirst site. It works great for html, images, css and javascript. </p> <p>I post the filter next. It checks if GZIP is an accepted encoding and it adds gzip as Content-Encoding. See: <code>wrappedResp.setHeader("Content-Encoding", "gzip");</code></p> <pre><code>public class CompressionFilter implements Filter { private ServletContext ctx; private FilterConfig cfg; /** * The init method saves the config object and a quick reference to the * servlet context object (for logging purposes). */ public void init(FilterConfig cfg) throws ServletException { this.cfg = cfg; ctx = cfg.getServletContext(); //ctx.log(cfg.getFilterName() + " initialized."); } /** * The heart of this filter wraps the response object with a Decorator * that wraps the output stream with a compression I/O stream. * Compression of the output stream is only performed if and only if * the client includes an Accept-Encoding header (specifically, for gzip). */ public void doFilter(ServletRequest req, ServletResponse resp, FilterChain fc) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; // Dose the client accept GZIP compression? String valid_encodings = request.getHeader("Accept-Encoding"); if ( (valid_encodings != null) &amp;&amp; (valid_encodings.indexOf("gzip") &gt; -1) ) { // Then wrap the response object with a compression wrapper // We'll look at this class in a minute. CompressionResponseWrapper wrappedResp = new CompressionResponseWrapper(response); // Declare that the response content is being GZIP encoded. wrappedResp.setHeader("Content-Encoding", "gzip"); // Chain to the next component (thus processing the request) fc.doFilter(request, wrappedResp); // A GZIP compression stream must be "finished" which also // flushes the GZIP stream buffer which sends all of its // data to the original response stream. GZIPOutputStream gzos = wrappedResp.getGZIPOutputStream(); gzos.finish(); // The container handles the rest of the work. //ctx.log(cfg.getFilterName() + ": finished the request."); } else { fc.doFilter(request, response); //ctx.log(cfg.getFilterName() + ": no encoding performed."); } } public void destroy() { // nulling out my instance variables cfg = null; ctx = null; } } </code></pre> <p>I was using the next code to send JSON responses in Struts web application. </p> <pre><code>public ActionForward get(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) { JSONObject json = // Do some logic here RequestUtils.populateWithJSON(response, json); return null; } public static void populateWithJSON(HttpServletResponse response,JSONObject json) { if(json!=null) { response.setContentType("text/x-json;charset=UTF-8"); response.setHeader("Cache-Control", "no-cache"); try { response.getWriter().write(json.toString()); } catch (IOException e) { throw new ApplicationException("IOException in populateWithJSON", e); } } } </code></pre> <p>It works fine without compression but if I compress JSON responses, I can not see my JSON objects anymore. I handle JSON Ajax calls with JQuery with code snippets as follows: </p> <pre><code> $.post(url,parameters, function(json) { // Do some DOM manipulation with the data contained in the JSON Object }, "json"); </code></pre> <p>If I see the response with Firebug it is empty. </p> <p>Should I refractor my compression filter to skip compression in JSON responses? or there is a workaround to this?</p> <p>For me, it looks like JQuery does not recognize the response as JSON because I am adding the Gzip compression. </p>
 

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