Read JSON message from HTTP POST request in Java

Question

I am new to Java and to client- server programming.

I am using embedded Jetty, and I'm trying to send a JSON string to some address (http://localhost:7070/json) and then to display the JSON string in that address.

I tried the following code but all I get is null.

Embedded Jetty code:

public static void main(String[] args) throws Exception {
    Server server = new Server(7070);
    ServletContextHandler handler = new ServletContextHandler(server, "/json");
    handler.addServlet(ExampleServlet.class, "/");
    server.start();
}

Client side function for sending the Http POST:

public static void sendHttp(){
    HttpClient httpClient = HttpClientBuilder.create().build(); //Use this instead 

    try {
        HttpPost request = new HttpPost("http://localhost:7070/json");

        JSONObject object = new JSONObject();
        try {
            object.put("name", "MyName");
            object.put("age", "26");
        } catch (Exception ex) {
            System.out.println("Error: " + ex.getMessage());
        }

        String message = object.toString();
        request.setEntity(new StringEntity(message, "UTF8"));
        request.setHeader("Content-type", "application/json");

        HttpResponse response = httpClient.execute(request);

        // handle response here...
    }catch (Exception ex) {
        // handle exception here
    } finally {
    }
}

And Servlet functions:

public class ExampleServlet extends HttpServlet{

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        //System.out.println("test get\n");
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        //System.out.println("test post\n");
        PrintWriter out = resp.getWriter();
        String json_str = req.getParameter("name");
        out.print(json_str);
    }
}

I call the sendHttp() method from a test class, after running the embedded Jetty server code (if that matters).

Answer 1

To get the data from a Post request you need to obtain the content. Try this:

String data = IOUtils.toString(req.getInputStream(), "UTF-8");

Answer 2

You need to read the raw request body as below. Put this inside your doPost method of servlet for reading json from the request:

StringBuilder jsonBuff = new StringBuilder();
String line = null;
try {
    BufferedReader reader = req.getReader();
    while ((line = reader.readLine()) != null)
        jsonBuff.append(line);
} catch (Exception e) { /*error*/ }

System.out.println("Request JSON string :" + jsonBuff.toString());
//write the response here by getting JSON from jasonBuff.toString()

try {
    JSONObject jsonObject = JSONObject.fromObject(jb.toString());

    out.print(jsonObject.get("name"));//writing output as you did

} catch (ParseException e) {
    throw new IOException("Error parsing JSON ");
}

Note : You can access req.getParameter("name"); only when your headers would be like this:

content type: "application/x-www-form-urlencoded"

as in normal html form submission.