Enviamos una petición POST a un API Rest, http://equisd.com/consumir-api-rest-con-android-listview/

android-post-volley-data.java

    public static void sendRequestPOST(QueueUtils.QueueObject o, final MainActivity _interface) {
        String url = "http://rrojasen.alwaysdata.net/purchaseorders.json";
        url = "http://fipo.equisd.com/api/users/new.json";
        url = "http://192.168.58.3:8056/api/users/new.json";
        StringRequest stringRequest = new StringRequest(Request.Method.POST, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        try {
                            //Do it with this it will work
                            JSONObject _response = new JSONObject(response);
                            if (_response.has("object")) {
                                JSONObject object_response = null;
                                try {
                                    object_response = _response.getJSONObject("data");
                                } catch (JSONException e) {
                                    e.printStackTrace();
                                }

                                if ( object_response != null ) {
                                    try {
                                        System.out.println(object_response.getInt("id"));
                                    } catch (JSONException e) {
                                        e.printStackTrace();
                                    }
                                }
                            }

                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                    }
                }){
            @Override
            protected Map<String,String> getParams(){
                Map<String,String> params = new HashMap<String, String>();
                params.put("first_name","aaa");
                params.put("last_name","ddd");
                params.put("avatar","xxx");

                return params;
            }
        };
        o.addToRequestQueue(stringRequest);
    }

android-post-volley.java

public static void sendRequestPOST(QueueUtils.QueueObject o, final MainActivity _interface) {
    String url = "http://rrojasen.alwaysdata.net/purchaseorders.json";
    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest
            (Request.Method.POST, url, null, new Response.Listener<JSONObject>() {

                @Override
                public void onResponse(JSONObject response) {
                    if (response.has("data")) {
                        JSONObject object_response = null;
                        try {
                            object_response = response.getJSONObject("data");
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }

                        if ( object_response != null ) {
                            try {
                                System.out.println(object_response.getInt("id"));
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }, new Response.ErrorListener() {

                @Override
                public void onErrorResponse(VolleyError error) {
                    // TODO: Handle error
                }
            });
    o.addToRequestQueue(jsonObjectRequest);
}

important-code-for-post-request.java

    public static void sendRequestPOST(QueueUtils.QueueObject o, final MainActivity _interface) {
        String url = "http://rrojasen.alwaysdata.net/purchaseorders.json";
        url = "http://fipo.equisd.com/api/users/new.json";
        url = "http://192.168.58.3:8056/api/users/new.json";
        StringRequest stringRequest = new StringRequest(Request.Method.POST, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        //Here your code when the request is successful 
                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        //Here your code when the request was going fatal
                    }
                }){
            @Override
            protected Map<String,String> getParams(){
                Map<String,String> params = new HashMap<String, String>();
                params.put("first_name","aaa");
                params.put("last_name","ddd");
                params.put("avatar","xxx");

                return params;
            }
        };
        o.addToRequestQueue(stringRequest);
    }