HttpServletRequest get JSON POST data [duplicate]

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.

Lectra

This is simple method to get request data request.getReader().lines().collect(Collectors.joining()) – Maduro

the above mentioned throws stream already closed exception – Thyestes

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() – Uraeus

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<T>. What you end up with is: new ObjectMapper().readValue(request.getReader(), YourBodyType.class) - and there you have it. Short and slick. – Thermophone

Answer 1

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...
}

Everglades

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. – Friede

That's correct you can read the request body content only once. – Everglades

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. – Freesia

Why not just to pass getReader() to json parser as here: https://mcmap.net/q/151471/-retrieving-json-object-literal-from-httpservletrequest ? This wouldn't require extra copy loop. – Hasheem

JSONObject jsonObject = HTTP.toJSONObject(jb.toString()); toJSONObject must have been moved to be a static method in the org.json.HTTP class – Catchall

Why I cannot find the fromObject(String string) method inside the documentation? json.org/javadoc/org/json/JSONObject.html – Woodworking

@X.Li, see the comment directly above yours. – Buffy

You can use StringBuilder here, and you need close reader in finally block. Just in case :) – Jugoslavia

Should be: JSONObject jsonObject = new JSONObject(jb.toString()); – Polled

get POST body BufferedReader reader = request.getReader(); – Margret

Answer 2

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

Seymourseys