You just have to make a JSONObject from your HashMap of parameters:
String url = "https://www.youraddress.com/";
Map<String, String> params = new HashMap();
params.put("first_param", 1);
params.put("second_param", 2);
JSONObject parameters = new JSONObject(params);
JsonObjectRequest jsonRequest = new JsonObjectRequest(Request.Method.POST, url, parameters, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
//TODO: handle success
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
error.printStackTrace();
//TODO: handle failure
}
});
Volley.newRequestQueue(this).add(jsonRequest);