StringRequest jsonObjRequest = new StringRequest(Request.Method.POST, URL,
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    System.out.println("hellooo");
                }
            }, new Response.ErrorListener() {

        @Override
        public void onErrorResponse(VolleyError error) {
            System.out.println("error");
        }
    }) {

        @Override
        public String getBodyContentType() {
            return "application/x-www-form-urlencoded; charset=UTF-8";
        }

        @Override
        protected Map<String, String> getParams() throws AuthFailureError {
            Map<String, String> params = new HashMap<String, String>();
            params.put("username", "hello");
            params.put("password", "hellooo");
            return params;
        }
    };

    queue.add(jsonObjRequest);

Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

    testAPI testapi = retrofit.create(testAPI.class);

    String hello = "hello";

    Call<Message> call = testapi.sendData(hello);

    call.enqueue(new Callback<Message>() {
        @Override
        public void onResponse(Response<Message> response) {
            System.out.println(response);
        }

        @Override
        public void onFailure(Throwable t) {
            System.out.println(t);
        }
    });

Ion.with(getContext())
    .load("https://koush.clockworkmod.com/test/echo")
    .setBodyParameter("goop", "noop")
    .setBodyParameter("foo", "bar")
    .asString()
    .setCallback(...)