How to retrieve raw post data from HttpServletRequest in java

The request body is available as byte stream by HttpServletRequest#getInputStream():

InputStream body = request.getInputStream();
// ...

Or as character stream by HttpServletRequest#getReader():

Reader body = request.getReader();
// ...

Note that you can read it only once. The client ain't going to resend the same request multiple times. Calling getParameter() and so on will implicitly also read it. If you need to break down parameters later on, you've got to store the body somewhere and process yourself.

We had a situation where IE forced us to post as text/plain, so we had to manually parse the parameters using getReader. The servlet was being used for long polling, so when AsyncContext::dispatch was executed after a delay, it was literally reposting the request empty handed.

So I just stored the post in the request when it first appeared by using HttpServletRequest::setAttribute. The getReader method empties the buffer, where getParameter empties the buffer too but stores the parameters automagically.

    String input = null;

    // we have to store the string, which can only be read one time, because when the
    // servlet awakens an AsyncContext, it reposts the request and returns here empty handed
    if ((input = (String) request.getAttribute("com.xp.input")) == null) {
        StringBuilder buffer = new StringBuilder();
        BufferedReader reader = request.getReader();

        String line;
        while((line = reader.readLine()) != null){
            buffer.append(line);
        }
        // reqBytes = buffer.toString().getBytes();

        input = buffer.toString();
        request.setAttribute("com.xp.input", input);
    }

    if (input == null) {
        response.setContentType("text/plain");
        PrintWriter out = response.getWriter();
        out.print("{\"act\":\"fail\",\"msg\":\"invalid\"}");
    }