How can I connect my app to MS SQL database?

Question

I am trying to create app that can connect to a MS SQL database when the user enters his username and password, I have tried multiple times and just cannot succeed. What would be the best way to connect my app?

This is the code that I have tried below.

public class LoginActivity extends AppCompatActivity {

    private static String ip = "myip";
    private static String port = "myportnum";
    private static String Class = "net.sourceforge.jtds.jtbc.Driver";
    private static String database = "name";
    private static String username = "name";
    private static String password = "password";
    private static String url = "jdbc:jtds:sqlserver://"+ip+":"+port+"/"+database;

    private Connection connection = null;




    private EditText userNameET, passwordEt;
    private Button loginBTN;



        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_login);


            userNameET = findViewById(R.id.userNameEditText);
            passwordEt = findViewById(R.id.passEditText);

            loginBTN = findViewById(R.id.loginBtn);


            StrictMode.ThreadPolicy policy = null;
            policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);


        }



   // @android.support.annotation.RequiresApi(api = Build.VERSION_CODES.CUPCAKE)
    private class DoLoginForUser extends AsyncTask<String, Void, String> {
        String emailId, password;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            emailId = userNameET.getText().toString();
            password = passwordEt.getText().toString();
           // progressBar.setVisibility(View.VISIBLE);
            loginBTN.setVisibility(View.GONE);
        }

        @Override
        protected String doInBackground(String... params) {

            try {
                ConnectionHelper con = new ConnectionHelper();
                Connection connect = ConnectionHelper.CONN();

                String query = "Select * from testDatabase where UserId='" + emailId + "'";
                PreparedStatement ps = connect.prepareStatement(query);

                Log.e("query",query);
                ResultSet rs = ps.executeQuery();
                if (rs.next()) {
                    String passcode = rs.getString("password");
                    connect.close();
                    rs.close();
                    ps.close();
                    if (passcode != null && !passcode.trim().equals("") && passcode.equals(password))
                        return "success";
                    else
                        return "Invalid Credentials";

                } else
                    return "User does not exists.";
            } catch (Exception e) {

                return "Error:" + e.getMessage();
            }
        }

        @Override
        protected void onPostExecute(String result) {

            //Toast.makeText(signup.this, result, Toast.LENGTH_SHORT).show();
           // ShowSnackBar(result);
           // progressBar.setVisibility(View.GONE);
            loginBTN.setVisibility(View.VISIBLE);
            if (result.equals("success")) {
                SharedPreferences sharedPreferences = getApplicationContext().getSharedPreferences("userdetails",0);
                SharedPreferences.Editor editor = sharedPreferences.edit();

                editor.putString("email",userNameET.getText().toString());

                editor.commit();

                Intent i = new Intent(LoginActivity.this, MainActivity.class);
                startActivity(i);

            } else {
                //ShowSnackBar(result);
            }
        }
    }

    //public void ShowSnackBar(String message) {
      //  Snackbar.make(lvparent, message, Snackbar.LENGTH_LONG)
               // .setAction("CLOSE", new View.OnClickListener() {
                 //   @Override
                //    public void onClick(View view) {

              ////      }
            //    })
            //    .setActionTextColor(getResources().getColor(android.R.color.holo_red_light))

           //     .show();
   // }

    public void DoLogin(View v)
    {
        DoLoginForUser login = null;
        login = new DoLoginForUser();
        login.execute("");
    }

I am expecting it to connect and then take me to the next screen.