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 · Accepted 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

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

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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