java Oracle Sql Server MySql 数据库连接

package com.dao.impl;

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

public class ConnDriver {

 private static String url;
 private static String username;
 private static String password;
 static{
  /*
   *
     String oracleUrl = "jdbc:oracle:thin:@localhost:1521:orcl";// orcl 为sid 
        String mySqlUrl = "jdbc:mysql://localhost/test";//test 为数据库名 
        String sqlServerUrl = "jdbc:sqlserver://localhost:1433; DatabaseName=test"; 
   */
  url = "";
  username ="sa";
  password="sa";
 }
 public static void main(String[] args) throws SQLException {

Class.forName("") ;   
  Connection conn = DriverManager.getConnection(url,username,password);
  Statement st = conn.createStatement();
  ResultSet rs = null;
  try {
   rs = st.executeQuery("Select * from user");
   while (rs.next()) {
    System.out.println("id"+rs.getString(1));
    System.out.println("name"+rs.getString(2));
   }
  } finally{
   rs.close();
   st.close();
   conn.close();
  }
  
  
 }

}