title: How to send Json-rpc via retrofit2?
body: <p>I tried send <code>json-rpc</code> via <code>retrofit2</code>.
  This is my interface:</p>
  
  <pre><code>public interface ApiInterfaceJson {
  
  @POST
  @Headers( "Content-Type: application/json" )
  Call&lt;String&gt; getDataJson(
           @Url String url,
           @Body RequestBody body);
  </code></pre>
  
  <p>}</p>
  
  <p>Create <code>retrofit</code>:</p>
  
  <pre><code>retrofitJson = new Retrofit.Builder()
              .addConverterFactory(ScalarsConverterFactory.create())
              .baseUrl("http://localhost:8800")
              .client(client)
              .build();
  
      apiInterfaceJson   = retrofitJson.create(ApiInterfaceJson.class);
  </code></pre>
  
  <p>Call:</p>
  
  <pre><code>JSONObject paramObject = new JSONObject();
      try {
          paramObject.put("id", "0");
          paramObject.put("name", "user");
          paramObject.put("command", "finish");
      }catch(Exception e){
      }   
    RequestBody requestBody=  RequestBody.create(MediaType.parse("application/json"), paramObject.toString());       
  MinersMonitorApplication.getApiJson().getDataJson("http://10.10.10.230:10000", requestBody).enqueue(new Callback&lt;String&gt;() {
              @Override
              public void onResponse(@NonNull Call&lt;String&gt; call, @NonNull Response&lt;String&gt; response) {}              
              @Override
              public void onFailure(Call&lt;String&gt; call, Throwable t) {
              }
          });
  </code></pre>
  
  <p>The result is <code>SocketTimeoutException</code>.</p>