Why Android connect to SQL db is not working

Question

I tried to connect my android app to SQL DB using JDBC connector. If I try it in Netbeans, so it's OK and the connection is working. I am using connector: mssql-jdbc-8.2.2.jre13

package sql_server;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class Sql_server {

    public static void main(String[] args) {
        String url = "jdbc:sqlserver://localhost\\MSSQLSERVER19;databaseName=Helios002";
        String user = "user";
        String password = "password";

        String query = "select top 1 skupzbo, regcis, nazev1 from Tabkmenzbozi order by id desc";

        try ( Connection con = DriverManager.getConnection(url, user, password);  Statement st = con.createStatement();  ResultSet rs = st.executeQuery(query)) {
            if (rs.next()) {
                System.out.println(rs.getString(1) + rs.getString(2) + rs.getString(3));
            }
        } catch (SQLException ex) {
            System.out.println("An error occurred while connecting MySQL databse");
            ex.printStackTrace();
        }
    }
}

But in android studio it's not working.I am using connector:mssql-jdbc-8.2.2.jre11, because mssql-jdbc-8.2.2.jre13 is not supported by android studio.

package com.example.hepopr.ui.gallery;

import android.os.AsyncTask;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import com.example.hepopr.R;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Objects;
import java.util.Timer;
import java.util.TimerTask;

public class GalleryFragment extends Fragment {

    private TextView test;
    public static String url = "jdbc:sqlserver://localhost\\MSSQLSERVER19;databaseName=Helios002";
    public static final String user = "user";
    public static final String pass = "password";

    private GalleryViewModel galleryViewModel;

    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        galleryViewModel =
                ViewModelProviders.of( this ).get( GalleryViewModel.class );
        View root = inflater.inflate( R.layout.fragment_gallery, container, false );
        final TextView textView = root.findViewById( R.id.text_gallery );
        galleryViewModel.getText().observe( getViewLifecycleOwner(), new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
                textView.setText( s );
            }
        } );

        test=root.findViewById( R.id.textView2 );


        return root;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );

        Timer timer = new Timer();
        //Set the schedule function
        timer.scheduleAtFixedRate( new TimerTask() {
            @Override
            public void run() {
                new MyTask().execute();

            }
        },0, 30000 );   // 1000 Millisecond  = 1 second

    }


    private class MyTask extends AsyncTask<Void, Void, Void> {
        private String STvody = "", STvzduchu = "", SVlhkost = "", SCerpadlo = "", SHladina = "", SSvetlo = "", SDate = "", STlak = "";

        @Override
        protected Void doInBackground(Void... arg0) {

            try {
                Class.forName( "com.microsoft.sqlserver.jdbc.SQLServerDriver" );
                Connection con = DriverManager.getConnection( url, user,pass);
                if (con == null) {
                    Toast.makeText( getActivity(), "Nepřipojeno", Toast.LENGTH_SHORT ).show();
                } else {
                    Statement st = con.createStatement();
                    String sql = "select top 1 regcis from Tabkmenzbozi order by id desc ";

                    final ResultSet rs = st.executeQuery( sql );
                    if (rs == null) {
                        Toast.makeText( getActivity(), "Bez dat", Toast.LENGTH_SHORT ).show();
                    }
                    Objects.requireNonNull( rs ).next();
                    SDate = rs.getString( 1 );

                    String pattern = "HH:mm:ss";
                    DateFormat df = new SimpleDateFormat(pattern);
                    Date today = Calendar.getInstance().getTime();
                   // todayAsString = df.format( today );
                    con.close();
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            test.setText( SDate );
            super.onPostExecute( result );
        }
    }
}

And studio returns an error:

W/System.err: com.microsoft.sqlserver.jdbc.SQLServerException: The connection to the host localhost, named instance mssqlserver19 failed. Error: "java.net.SocketTimeoutException: Poll timed out". Verify the server and instance names and check that no firewall is blocking UDP traffic to port 1434.  For SQL Server 2005 or later, verify that the SQL Server Browser Service is running on the host.
W/System.err:     at com.microsoft.sqlserver.jdbc.SQLServerConnection.getInstancePort(SQLServerConnection.java:6068)
        at com.microsoft.sqlserver.jdbc.SQLServerConnection.primaryPermissionCheck(SQLServerConnection.java:2457)
W/System.err:     at com.microsoft.sqlserver.jdbc.SQLServerConnection.login(SQLServerConnection.java:2200)
        at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectInternal(SQLServerConnection.java:2067)
        at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:1204)
W/System.err:     at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:825)
        at java.sql.DriverManager.getConnection(DriverManager.java:569)
        at java.sql.DriverManager.getConnection(DriverManager.java:219)
W/System.err:     at com.example.hepopr.ui.gallery.GalleryFragment$MyTask.doInBackground(GalleryFragment.java:84)
        at com.example.hepopr.ui.gallery.GalleryFragment$MyTask.doInBackground(GalleryFragment.java:76)
W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:333)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
W/System.err:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:764)

Can you help me, what wrong is? Thank you.

Answer 1

Don't do this. Ever. Your db password is in your code, which is going out to devices. That means with 30 minutes of effort anyone can get your db password and screw with your data. You should only ever interact with a remote db through a webservice, so only the webservice (on your hardware) has the keys to your database. Anything else is incredibly insecure.

JDBC can be used server side securely because its only run on your server. But it should never be used on devices you don't physically control.