However, I want to compress my responses with GZIP wheren possible. I tried using the Compression filter code available for free download in the headfirst site. It works great for html, images, css and javascript.
I post the filter next. It checks if GZIP is an accepted encoding and it adds gzip as Content-Encoding. See: wrappedResp.setHeader("Content-Encoding", "gzip");
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) && (valid_encodings.indexOf("gzip") > -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;
}
}
I was using the next code to send JSON responses in Struts web application.
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);
}
}
}
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:
$.post(url,parameters, function(json) {
// Do some DOM manipulation with the data contained in the JSON Object
}, "json");
If I see the response with Firebug it is empty.
Should I refractor my compression filter to skip compression in JSON responses? or there is a workaround to this?
For me, it looks like JQuery does not recognize the response as JSON because I am adding the Gzip compression.