Java JDBC connection error: Communication link failure

Question

I'm working with JDBC for past 2 days now. But still not succeeded to make a successful connection with the database. here is the code for making a database connection:

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

public class DBConnector {

Connection conn = null;
public static String SERVER_NAME = "localhost";
public static String PORT_NUMBER = "3306";
public static String DATABASE_NAME = "TemporaryDatabase";
public String uri = "jdbc:mysql://" + SERVER_NAME + ":" + PORT_NUMBER + "/" + DATABASE_NAME;

public String username = "root";
public String password = "";

public DBConnector() {
}

public boolean Connect() {

    try {

        if (init()) {
            conn = DriverManager.getConnection(uri, username, password);
            return true;

        } else {
            System.out.println("Can not load driver.");
            return false;
        }
    } catch (SQLException se) {
        se.printStackTrace();
        return false;
    } catch (Exception e) {
        e.printStackTrace();
        return false;
    }

}

public static boolean init() {
    String driverName = "com.mysql.jdbc.Driver"; // for MySql

    try {
        Class.forName(driverName);
        return true;

    } catch (ClassNotFoundException e) {
        e.printStackTrace();
        return false;
    }

}

}

And here are the errors I'm getting when I run this piece of code:

  com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:981)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:339)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2253)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2286)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2085)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)
    at java.sql.DriverManager.getConnection(DriverManager.java:571)
    at java.sql.DriverManager.getConnection(DriverManager.java:215)
    at DBConnector.Connect(DBConnector.java:24)
    at WebCrawler.main(WebCrawler.java:37)
Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.connect0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:579)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:298)
    ... 16 more
CONNECTION: false

I'm using MS SQL Server 2012. Can anyone please let me know where I'm doing it wrong. I guess its with the username and password but I don't know the correct ones either. I'm working this with the default SQL server instance.

Answer 1

You're using SQL Server but your JDBC url is for MySQL. The correct JDBC url form for SQL Server is like following:

jdbc:sqlserver://[serverName[\instanceName][:portNumber]][;property=value[;property=value]]

For example:

jdbc:sqlserver://localhost:1433;databaseName=TemporaryDatabase

Also you shoud use SQL Server's JDBC driver instead of MySQL's. You could find the driver here and information about SQL Server connection strings here.