EditText username,password;
String uname,pwd;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    username = (EditText) findViewById(R.id.username);
    password = (EditText) findViewById(R.id.password);
}

public void invokeLogin(View view){
        uname = username.getText().toString();
        pwd = password.getText().toString();
        login(uname, pwd);
    }
public void login(final String uname, String pwd) {

    class loginAsync extends AsyncTask<String, Void, String> {
        private Dialog loadDialogue;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            loadDialogue = ProgressDialog.show(LoginActivity.this, "Please wait...", "Loading");
        }

        @Override
        protected String doInBackground(String... params) {
            JSONObject jsonObject;
            String result="";

            try {

                URL url = new URL("https://localhost/Android App/Login.php");
                jsonObject = new JSONObject();
                jsonObject.put("uname", params[0]);
                jsonObject.put("pwd", params[1]);
                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                httpURLConnection.setReadTimeout(15000);
                httpURLConnection.setConnectTimeout(15000);
                httpURLConnection.setDoInput(true);
                httpURLConnection.setDoOutput(true);
                OutputStream outputStream = httpURLConnection.getOutputStream();
                BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
                writer.write(getPostDataString(jsonObject));
                writer.flush();
                writer.close();
                outputStream.close();
                int responsecode = httpURLConnection.getResponseCode();

                if (responsecode == HttpURLConnection.HTTP_OK) {

                    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
                    StringBuilder sb = new StringBuilder(" ");
                    String line;
                    while ((line = bufferedReader.readLine()) != null) {

                        sb.append(line);
                    }
                    bufferedReader.close();
                    result = sb.toString();
                }
                else {
                    return new String("false " + responsecode);
                }

            }
            catch (NullPointerException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return result;
        }
        @Override
        protected void onPostExecute(String result) {
            String s = result.trim();
            loadDialogue.dismiss();
            if(s.equalsIgnoreCase("success")){
                Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                finish();
                startActivity(intent);
            }else {
                Toast.makeText(getApplicationContext(), "Invalid User Name or Password", Toast.LENGTH_LONG).show();
            }
        }
    }
}
public String getPostDataString(JSONObject params) throws Exception {
    StringBuilder result = new StringBuilder();
    boolean first = true;
    Iterator<String> itr = params.keys();
    while (itr.hasNext()) {
        String key = itr.next();
        Object value = params.get(key);
        if (first)
            first = false;
        else {
            result.append("&");
            result.append(URLEncoder.encode(key, "UTF-8"));
            result.append("=");
            result.append(URLEncoder.encode(value.toString(), "UTF-8"));
        }
    }
    return result.toString();
}