Develop Reference

Does a HttpServlet have to respond to a request?

I have several servlets that do things server side. On a few I just encode some unnecessary data and send it back, which seems pointless. Do you have to respond ? What happens when you just say return ? I've done that before and nothing seems to go wrong but I am relatively new to servlets. Are there consequences for simply returning that go above my head ? And what exactly happens when you return;
if(request.getParameter("name").equals("saveusedcards")) {
String sessId = request.getSession().getId();
//encode request with confirmation that cards were successfully updated
if(usersUpdatedCards.get(sessId).isEmpty()){
//no cards were seen
}
boolean success = DataDAO.updateCards(usersUpdatedCards.get(sessId));
if(success){
System.out.println("Data base update successfull!");
String responseMessage = new Gson().toJson("card successfully udpated");
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
System.out.println("updated cards response message: "+responseMessage);
response.getWriter().write(responseMessage);
return;
} else {
System.out.println("Data base update failed...");
String responseMessage = new Gson().toJson("card was not successfully updated");
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
System.out.println("updated cards response message: "+responseMessage);
response.getWriter().write(responseMessage);
return;
}
}

The servlet must produce an HTTP response for the client, however it is perfectly acceptable to return no content in the response body. When doing so your servlet should make this clear to the client by sending a response code of 204 (no content). Reference: https://httpstatuses.com/204
Here is an example of how you would set the response code from the doGet method. You could do the same from doPost or service methods.
#Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
// Do whatever work you need to do here...
res.setStatus(HttpServletResponse. SC_NO_CONTENT); // This returns a 204
}

How to get the content from Twilio response message

#RequestMapping(value = {"sms"},method = RequestMethod.POST)
public string rplyMessage(HttpServletRequest request, HttpServletResponse response) throws IOException {
Body body = new Body.Builder("Response message").build();
Message sms =
new Message.Builder().body(body).build();
MessagingResponse twiml = new MessagingResponse.Builder().message(sms).build();
response.setContentType("application/xml");
try {
response.getWriter().print(twiml.toXml());
} catch (TwiMLException e) {
e.printStackTrace();
}
}
This is how I handle the twilio response message.I want to get the content from the response message. and i want to store it in the database.How I can get the content from the response message.

Twilio developer evangelist here.
When Twilio makes a request to your application it sends the parameters encoded as application/x-www-form-urlencoded in the body of the POST request.
I've never written Java Spring MVC before, so excuse me if this isn't spot on, but I believe you can then read those parameters out of the body using the #RequestParam annotation.
#RequestMapping(value = {"sms"},method = RequestMethod.POST)
public string rplyMessage(
HttpServletRequest request,
HttpServletResponse response,
#RequestParam("Body") String message,
#RequestParam("From") String from
) throws IOException {
storeMessage(from, message);
// respond to the request
}
The message body and the number that sent it are the parameters "Body" and "From", you can see all the available request parameters here. So, for example with the message, you set the argument to #RequestParam to the name of the parameter, then you set the type and what you want the variable to be called within the method, thus: #RequestParam("Body") String message.
I don't know how you plan to use the database, but that's what I can tell you. You can read more about #RequestParam here and see some Twilio Java and Spring tutorials here.
Let me know if that helps at all.

Authorization redirect on session expiration does not work on submitting a JSF form, page stays the same

I am using JSF2. I have implemented a custom faces servlet like so:
public class MyFacesServletWrapper extends MyFacesServlet {
// ...
}
wherein I'm doing some authorization checks and sending a redirect when the user is not logged in:
public void service(ServletRequest request, ServletResponse response) {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
if (...) {
String loginURL = req.getContextPath() + "/LoginPage.faces";
res.sendRedirect(loginURL);
}
}
This works when the user tries to navigate to another page. However, this does not work when a JSF form is submitted by a JSF command link/button. The line sendRedirect() line is hit and executed, no exception is been thrown, but the user stays at the same page. Basically, there's no visual change at all.
Why does this work on page navigation, but not on form submit?

Your concrete problem is most likely caused because your JSF command link/button is actually sending an ajax request which in turn expects a special XML response. If you're sending a redirect as response to an ajax request, then it would just re-send the ajax request to that URL. This in turn fails without feedback because the redirect URL returns a whole HTML page instead of a special XML response. You should actually be returning a special XML response wherein the JSF ajax engine is been instructed to change the current window.location.
But you've actually bigger problems: using the wrong tool for the job. You should use a servlet filter for the job, not a homegrown servlet and for sure not one which supplants the FacesServlet who is the responsible for all the JSF works.
Assuming that you're performing the login in a request/view scoped JSF backing bean as follows (if you're using container managed authentication, see also 2nd example of Performing user authentication in Java EE / JSF using j_security_check):
externalContext.getSessionMap().put("user", user);
Then this kickoff example of a filter should do:
#WebFilter("/*") // Or #WebFilter(servletNames={"facesServlet"})
public class AuthorizationFilter implements Filter {
private static final String AJAX_REDIRECT_XML = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
+ "<partial-response><redirect url=\"%s\"></redirect></partial-response>";
#Override
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws ServletException, IOException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
HttpSession session = request.getSession(false);
String loginURL = request.getContextPath() + "/login.xhtml";
boolean loggedIn = (session != null) && (session.getAttribute("user") != null);
boolean loginRequest = request.getRequestURI().equals(loginURL);
boolean resourceRequest = request.getRequestURI().startsWith(request.getContextPath() + ResourceHandler.RESOURCE_IDENTIFIER + "/");
boolean ajaxRequest = "partial/ajax".equals(request.getHeader("Faces-Request"));
if (loggedIn || loginRequest || resourceRequest)) {
if (!resourceRequest) { // Prevent browser from caching restricted resources. See also https://stackoverflow.com/q/4194207/157882
response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); // HTTP 1.1.
response.setHeader("Pragma", "no-cache"); // HTTP 1.0.
response.setDateHeader("Expires", 0); // Proxies.
}
chain.doFilter(request, response); // So, just continue request.
}
else if (ajaxRequest) {
response.setContentType("text/xml");
response.setCharacterEncoding("UTF-8");
response.getWriter().printf(AJAX_REDIRECT_XML, loginURL); // So, return special XML response instructing JSF ajax to send a redirect.
}
else {
response.sendRedirect(loginURL); // So, just perform standard synchronous redirect.
}
}
// ...
}
See also:
Using JSF 2.0 / Facelets, is there a way to attach a global listener to all AJAX calls?
FullAjaxExceptionHandler does not show session expired error page on ajax button

FacesContext.getCurrentInstance().getExternalContext().redirect("newpage.xhtml"); try this.... in place of res.sendredirect(cpath).

Converting GET method url's to logical permanent links

I have a J2EE application with a web service which goes like
http://servername/service?task=getFile&id=25
How can I convert these type of urls to
http://servername/service/getFile/25
http://servername/service/getFile/26
etc?
Please provide your suggestions.

You can use the UrlRewriteFilter in order to achieve this. You will just have to write the rules for rewriting, similar to mod_rewrite. For example:
<rule>
<from>^/products/([0-9]+)$</from>
<to>/products/index.jsp?product_id=$1</to>
</rule>

To the point, you thus want to forward the friendly URL to an unfriendly URL (so that you don't need to change existing request parameter collecting logic of the servlet) and to redirect the unfriendly URL to an friendly URL (so that the friendly URL get reflected in the browser address bar of the client).
The best place for this is a Filter. To access the HttpServletRequest, just downcast ServletRequest to HttpServletRequest. You can get the query string by getQueryString() and you can get the pathinfo by getRequestURI(). Here's a kickoff example:
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException
{
HttpServletRequest httpreq = (HttpServletRequest) request;
String query = httpreq.getQueryString();
if (query != null) {
// Unfriendly URL invoked. Convert params to pathinfo and redirect.
StringBuffer newURL = httpreq.getRequestURL();
for (String param : query.split("&")) {
newURL.append('/').append(param.substring(param.indexOf('=') + 1));
}
((HttpServletResponse) response).sendRedirect(newURL.toString());
} else {
// Friendly URL invoked. Convert pathinfo to params and forward.
String[] parts = httpreq.getRequestURI().replace(httpreq.getContextPath(), "").split("/");
String newURL = String.format("%s?task=%s&id=%s", parts[1], parts[2], parts[3]);
httpreq.getRequestDispatcher(newURL).forward(request, response);
}
}
You can of course also grab the aforementioned UrlRewriteFilter.

Use GZIP, JSON responses and JQuery

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.

If I see the response with Firebug it
is empty.
There's your clue - it's not a JQuery problem, it's server-side. (I'm afraid I can't help you with that, other than to suggest you stop looking at the client-side)
There's no problem gzipping ajax responses - if you can't see the response in Firebug, then JQuery can't see it either.

you have to add one more header "content-encoding: gzip" if you are compressing it.

Have you tried with an explicit java-based client to ensure it's a problem with jQuery or browser? If java client fails, something is wrong with server response.
But I am guessing that whereas browser can deal with uncompression with direct requests, this is perhaps not applied to Ajax calls.
It's an interesting question, I hope we'll get a more definitive answer. :)