title: "return response.body().string() " is empty with okhttp3
body: <p>I created the following class:</p>
  
  <pre><code>package com.inverseo.marc.t372lematin;
  import java.io.IOException;
  import okhttp3.MediaType;
  import okhttp3.OkHttpClient;
  import okhttp3.Request;
  import okhttp3.RequestBody;
  import okhttp3.Response;
  
  
  public class PostJSON {
      public static final MediaType JSON
              = MediaType.parse("application/json; charset=utf-8");
  
      OkHttpClient client = new OkHttpClient();
      public String postJSONRequest(String url, String json) throws IOException {
          RequestBody body = RequestBody.create(JSON, json);
          Request request = new Request.Builder()
                  .url(url)
                  .post(body)
                  .build();
          Response response = client.newCall(request).execute();
          System.out.println("postJSONRequest response.body : "+response.body().string());
          return response.body().string() ;
      }   //postJSONRequete
  } //class PostJSON
  </code></pre>
  
  <p>It used to work from an activity where I write some data to MySQL on a server.
  And when I call it from the following  piece of code, I get an empty response !</p>
  
  <pre><code>      System.out.println("début appel "+getString(R.string.CF_URL)+"authentication2.php" );
          PostJSON client2 = new PostJSON();
          JSONObject obj = new JSONObject();
          try {
              obj.put("username", mUserName);
              obj.put("password", mPassword);
              obj.put("email", mEmail);
          } catch (JSONException e) {
              e.printStackTrace();
          }
          System.out.println("obj.toString()="+obj.toString());
          String response = null;
          try {
              response = client2.postJSONRequest(getString(R.string.CF_URL)+ "authentication2.php", obj.toString());
          } catch (IOException e) {
              e.printStackTrace();
              System.out.println("appel d'authentication2.php échoué : " + e);
          }
          System.out.println("fin authentication2, response = "+response);
          return response;
  </code></pre>
  
  <p>Here is what I get in logcat</p>
  
  <pre><code>02-25 05:52:24.938 26130-26226/com.inverseo.marc.t372lematin I/System.out: Accès à Internet : OK
  02-25 05:52:24.938 26130-26226/com.inverseo.marc.t372lematin I/System.out: début appel http://mywebsite.fr/Inverseo/authentication2.php
  02-25 05:52:24.938 26130-26226/com.inverseo.marc.t372lematin I/System.out: obj.toString()={"email":"xxx-ts@laposte.net","password":"xxx","username":"MarcUser"}
  02-25 05:52:25.068 26130-26130/com.inverseo.marc.t372lematin I/Choreographer: Skipped 30 frames!  The application may be doing too much work on its main thread.
  02-25 05:52:25.448 26130-26130/com.inverseo.marc.t372lematin I/Choreographer: Skipped 34 frames!  The application may be doing too much work on its main thread.
  02-25 05:52:27.898 26130-26226/com.inverseo.marc.t372lematin I/System.out: postJSONRequest response.body : {"result":1,"message":"AUTHENTICATION OK","Id_profile":"1394","DebutDerCycle":"2016-01-31"}
  02-25 05:52:27.898 26130-26226/com.inverseo.marc.t372lematin I/System.out: fin authentication2, response = 
  02-25 05:52:28.588 26130-26130/com.inverseo.marc.t372lematin I/Choreographer: Skipped 140 frames!  The application may be doing too much work on its main thread.
  </code></pre>
  
  <p>So to wrap it up, in my PostJSON class, I write the correct result to System.out. Then return it. But the response is then empty.
  I can't figure out why.</p>