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).

Maybe you should take a look at: stackoverflow.com/questions/11901831/… — kipzes
– kipzes, Commented Nov 24, 2015 at 14:35

jordi · Accepted Answer · 2015-11-24 14:37:52Z

2

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

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

answered Nov 24, 2015 at 14:37

jordi

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1 Comment

jordi Over a year ago

Check if you have import org.apache.commons.io.IOUtils;

Maytham Fahmi · Accepted Answer · 2017-04-06 08:51:51Z

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.

edited Apr 6, 2017 at 8:51

Maytham Fahmi

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answered Nov 24, 2015 at 15:28

Tom Sebastian

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3 Comments

Maya Over a year ago

not sure I got it - do I need to change request.setHeader("Content-type", "application/json"); to request.setHeader("Content-type", "application/x-www-form-urlencoded");?

Tom Sebastian Over a year ago

No you follow the first method. That is using req.getReader(). I put Note as an additional info.

Newbie Over a year ago

fromObject(jb.toString() Whyare you trying to make a JSONObject from an object then calling a string? Also jb is not defined. 10/10 for effort.

Anirudh R.Huilgol. · Accepted Answer · 2017-06-29 11:51:26Z

2

Here is my code this works fine

    String data = "";   
    StringBuilder builder = new StringBuilder();
    BufferedReader reader = request.getReader();
    String line;
    while ((line = reader.readLine()) != null) {
        builder.append(line);
    }
    data = builder.toString();
    JSONObject object = new JSONObject(data); 
   //or JSONArray array = new JSONArray(data); which ever the one you want

Good luck.....

edited Jun 29, 2017 at 11:51

answered Jun 29, 2017 at 9:40

Anirudh R.Huilgol.

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Comments

jordi · Accepted Answer · 2015-11-24 15:22:11Z

I have not used jetty but I have done similar comunications with this code (PUT, not POST):

URL url = new URL(desturl);
HttpURLConnection huc = (HttpURLConnection) url.openConnection();
huc.setRequestMethod("PUT");
byte[] postData = null; 
int postDataLength; 
huc.setDoOutput(true);
postData = data.getBytes( StandardCharsets.UTF_8 );
postDataLength = postData.length;
huc.setRequestProperty( "Content-Type", "application/json"); 
huc.setRequestProperty( "charset", "utf-8");
huc.setRequestProperty( "Content-Length", Integer.toString( postDataLength ));
huc.setUseCaches( false );
huc.connect();
huc.setConnectTimeout(10000);
DataOutputStream wr = new DataOutputStream( huc.getOutputStream());
wr.write( postData );
rd = new BufferedReader(new InputStreamReader(huc.getInputStream()));
retcode = huc.getResponseCode();

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