HttpServletRequest get JSON POST data

Question

I am HTTP POST-ing to URL http://laptop:8080/apollo/services/rpc?cmd=execute

with POST data

{ "jsondata" : "data" }

Http request has Content-Type of application/json; charset=UTF-8

How do I get the POST data (jsondata) from HttpServletRequest?

If I enumerate the request params, I can only see one param, which is "cmd", not the POST data.

This is simple method to get request data `request.getReader().lines().collect(Collectors.joining())` — Dmitry Stolbov, Feb 22 '17 at 06:17
If you use the `getReader()` the stream will get closed, since originally it can only be read once. There are a number of alternatives on Wrapper implementations to allow multiple calls to `getReader()` — Felipe Leão, Mar 05 '18 at 18:46
The easiest way you can solve this is using *Jackson*'s `ObjectMapper`. Its overloaded method `readValue` has a variation which accepts a `Reader` and a `Class`. What you end up with is: `new ObjectMapper().readValue(request.getReader(), YourBodyType.class)` - and there you have it. Short and slick. — Ionut Ciuta, Sep 25 '18 at 20:44

score 280 · Answer 1 · edited Jan 18 '17 at 10:02

280

Normaly you can GET and POST parameters in a servlet the same way:

request.getParameter("cmd");

But only if the POST data is encoded as key-value pairs of content type: "application/x-www-form-urlencoded" like when you use a standard HTML form.

If you use a different encoding schema for your post data, as in your case when you post a json data stream, you need to use a custom decoder that can process the raw datastream from:

BufferedReader reader = request.getReader();

Json post processing example (uses org.json package )

public void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {

  StringBuffer jb = new StringBuffer();
  String line = null;
  try {
    BufferedReader reader = request.getReader();
    while ((line = reader.readLine()) != null)
      jb.append(line);
  } catch (Exception e) { /*report an error*/ }

  try {
    JSONObject jsonObject =  HTTP.toJSONObject(jb.toString());
  } catch (JSONException e) {
    // crash and burn
    throw new IOException("Error parsing JSON request string");
  }

  // Work with the data using methods like...
  // int someInt = jsonObject.getInt("intParamName");
  // String someString = jsonObject.getString("stringParamName");
  // JSONObject nestedObj = jsonObject.getJSONObject("nestedObjName");
  // JSONArray arr = jsonObject.getJSONArray("arrayParamName");
  // etc...
}

edited Jan 18 '17 at 10:02

Ganesh Krishnan

7,155
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answered Sep 30 '10 at 14:53

Kdeveloper

13,679
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3

It seems like you can only get the post data from request.getReader *once*. Is this true? When I tried this myself, subsequent calls to get the post-data of the request fail. – B T Feb 16 '11 at 23:38
11

That's correct you can read the request body content only once. – Kdeveloper Feb 17 '11 at 11:56
this really saved my day...but what is getReader and how do the json data get populated there? is it specifically for JSON? or any other object ? any helpful links please. – rajesh_kw Mar 06 '14 at 10:03
Why not just to pass `getReader()` to json parser as here: http://stackoverflow.com/a/15109169/603516 ? This wouldn't require extra copy loop. – Vadzim Apr 28 '14 at 15:16
5

JSONObject jsonObject = HTTP.toJSONObject(jb.toString()); toJSONObject must have been moved to be a static method in the org.json.HTTP class – semisided1 Sep 26 '14 at 17:41
1

Why I cannot find the `fromObject(String string)` method inside the documentation? http://www.json.org/javadoc/org/json/JSONObject.html – XY L Feb 04 '15 at 08:42
1

@X.Li, see the comment directly above yours. – jds Feb 07 '15 at 22:15
You can use StringBuilder here, and you need close reader in finally block. Just in case :) – Mirimas Aug 27 '15 at 21:24
1

Should be: JSONObject jsonObject = new JSONObject(jb.toString()); – Newbie Jun 02 '17 at 03:49
get POST body `BufferedReader reader = request.getReader();` – Jul 02 '18 at 03:29

score -3 · Answer 2 · edited May 23 '17 at 12:26

Are you posting from a different source (so different port, or hostname)? If so, this very very recent topic I just answered might be helpful.

Odd jQuery problem - Ajax request to a C program not quite working

The problem was the XHR Cross Domain Policy, and a useful tip on how to get around it by using a technique called JSONP. The big downside is that JSONP does not support POST requests.

I know in the original post there is no mention of JavaScript, however JSON is usually used for JavaScript so that's why I jumped to that conclusion

HttpServletRequest get JSON POST data

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