How to Access JSON POST Data in a Servlet Using HttpServletRequest?

Accessing JSON POST Data in HttpServletRequest

When making an HTTP POST request with JSON data in the body, retrieving the request data can be a challenge if the traditional getParameter method is used. This is because getParameter only works with key-value pairs encoded in "application/x-www-form-urlencoded" format.

However, for JSON data streams, a custom approach is necessary.

Custom Decoder for JSON Data

To access the JSON POST data, you need to utilize BufferedReader to process the raw data stream:

BufferedReader reader = request.getReader();

Example Using org.json Package

Below is an example that uses the popular org.json library to decode JSON POST data:

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

  StringBuffer jb = new StringBuffer();
  String line = null;
  try {
    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");
  }
}

This code reads the JSON data and converts it into a JSONObject for further processing. You can then use methods like getInt, getString, and getJSONArray to extract the specific data you need.

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