Java failing to connect to a MariaDB database on localhost

Question

I'm trying to connect to my MariaDB database which is on localhost (using xampp). The first time I connect, the connection is established and I managed to create a table with the two fields "username" "password". Thereafter, when I try to do anything else, the Connection turns null and I cannot insert or execute any queries.

import java.sql.*;

class MyDatabase {
    private Connection conn;
    private PreparedStatement psAddPerson;


    MyDatabase(String host, String user, String password) throws Exception {
        Connection conn = DriverManager.getConnection("jdbc:mariadb:" + host,
                user, password);
        psAddPerson = null;
    }

    public void addPerson(String username, String password) {
        try{
            if( psAddPerson == null ){
                String sqlAddPerson = "insert into users (usern, pass) values (?,?)";
                psAddPerson = conn.prepareStatement(sqlAddPerson);
            }
            psAddPerson.setString(1, username);
            psAddPerson.setString(2, password);
            psAddPerson.executeUpdate();
        } catch (SQLException e) {
            System.err.println("Couldn't create add person");
            e.printStackTrace();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        String host = "//localhost:3306/test";
        String user = "root";
        String pass = "";
        MyDatabase newDb = null;
        try {
            newDb = new MyDatabase(host, user, pass);
        } catch (Exception e) {
            e.printStackTrace();
        }

        String username = "admin";
        String password = "password";
        if (newDb != null) {
            newDb.addPerson(username, password);
        }
    }
}

This code produces a NullPointerException when trying to execute following code:

psAddPerson = conn.prepareStatement(sqlAddPerson);

I want to be able to execute queries to my localhost database.

Picture from phpMyAdmin of server type:

Thanks

You're creating an instance of connection within the constructor, you need to initialize the instance variable `conn` — Ele, Dec 02 '17 at 11:13
Of course, it matters, the instance variable is always null because you're instantiating a local variable within the constructor. — Ele, Dec 02 '17 at 11:17

score 2 · Accepted Answer · answered Dec 02 '17 at 11:15

2

Change this:

Connection conn = DriverManager.getConnection("jdbc:mariadb:" + host, user, password);

by this:

conn = DriverManager.getConnection("jdbc:mariadb:" + host, user, password);

This way you're instantiating the instance variable rather than a local variable within the constructor.

Hope this helps!

answered Dec 02 '17 at 11:15

Ele

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Thank you :) You were faster than the other guy, so will accept yours as the answer – Cows42 Dec 02 '17 at 11:17
Good! :-) Happy coding time! – Ele Dec 02 '17 at 11:18

score 1 · Answer 2 · edited Dec 02 '17 at 14:30

1

The fix is easy change:

Connection conn = DriverManager.getConnection("jdbc:mariadb:" + host,
            user, password);

to:

conn = DriverManager.getConnection("jdbc:mariadb:" + host,
            user, password);

edited Dec 02 '17 at 14:30

Mark Rotteveel

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191
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answered Dec 02 '17 at 11:15

Saïd

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score 0 · Answer 3 · answered Dec 02 '17 at 14:22

0

Tweak it a little bit and change this :

Connection conn = DriverManager.getConnection("jdbc:mariadb:" + host, user, password);

to this:

conn = DriverManager.getConnection("jdbc:mariadb:" + host, user, password);

answered Dec 02 '17 at 14:22

Lucifer Rodstark

206
4
14

Java failing to connect to a MariaDB database on localhost

3 Answers3