Convenient way to parse incoming multipart/form-data parameters in a Servlet [duplicate]

Question

Is there any convenient way to read and parse data from incoming request.

E.g client initiate post request

URLConnection connection = new URL(url).openConnection(); connection.setDoOutput(true); connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary); PrintWriter writer = null; try {     OutputStream output = connection.getOutputStream();     writer = new PrintWriter(new OutputStreamWriter(output, charset), true); // true = autoFlush, important!     // Send normal param.     writer.println("--" + boundary);     writer.println("Content-Disposition: form-data; name=\"param\"");     writer.println("Content-Type: text/plain; charset=" + charset);     writer.println();     writer.println(param); 

I’m not able to get param using request.getParameter("paramName"). The following code

BufferedReader reader = new BufferedReader(new InputStreamReader(     request.getInputStream()));   StringBuilder sb = new StringBuilder();   for (String line; (line = reader.readLine()) != null;) {    System.out.println(line);    } 

however displays the content for me

-----------------------------29772313742745 Content-Disposition: form-data; name="name" J.Doe -----------------------------29772313742745 Content-Disposition: form-data; name="email" [email protected] -----------------------------29772313742745 

What is the best way to parse incoming request? I don’t want to write my own parser, probably there is a ready solution.

Answer 1

multipart/form-data encoded requests are indeed not by default supported by the Servlet API prior to version 3.0. The Servlet API parses the parameters by default using application/x-www-form-urlencoded encoding. When using a different encoding, the request.getParameter() calls will all return null. When you're already on Servlet 3.0 (Glassfish 3, Tomcat 7, etc), then you can use HttpServletRequest#getParts() instead. Also see this blog for extended examples.

Prior to Servlet 3.0, a de facto standard to parse multipart/form-data requests would be using Apache Commons FileUpload. Just carefully read its User Guide and Frequently Asked Questions sections to learn how to use it. I've posted an answer with a code example before here (it also contains an example targeting Servlet 3.0).