How to retrieve raw post data from HttpServletRequest in java

Question

I m trying to get the post data in Java  Seems like it should be one of the simplest things to do right  I mean  HttpServletRequest getParameter has to do it right  So how can you get the raw post data   I found HttpServletRequest get JSON POST data and used Kdeveloper s code to pull the post data from a request  It works  but theres a catch  I can only get that post data once   Heres the method I made from Kdeveloper s code   public static String getPostData HttpServletRequest req        StringBuilder sb   new StringBuilder        try           BufferedReader reader   req getReader            reader mark 10000            String line          do               line   reader readLine                sb append line  append   n              while  line    null           reader reset               do NOT close the reader here  or you won t be able to get the post data twice       catch IOException e            logger warn  getPostData couldn t   get the post data   e       This has happened if the request s reader is closed                return sb toString        Previously I had closed the reader at the end of this method  but that caused exceptions when the method ran more than once on the same request  Without closing it  no exceptions happen  but the method returns an empty string   Honestly  there should just be an exposed req getPostData   method - did no one think that would be useful   So how can I write this method such that it always returns the correct post data

User · Answer

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\"}");
    }

User · Answer

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

User · Answer

This worked for me   notice that java 8 is required   String requestData   request getReader   lines   collect Collectors joining     UserJsonParser u   gson fromJson requestData  UserJsonParser class     UserJsonParse is a class that shows gson how to parse the json formant   class is like that   public class UserJsonParser        private String username      private String name      private String lastname      private String mail      private String pass1    then put setters and getters     the json string that is parsed is like that    jsonData        username    testuser       pass1    clave1234      The rest of values  mail  lastname  name  are set to null

[java] How to retrieve raw post data from HttpServletRequest in java

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