java 连接 数据库 sql2008

我已经把 sql2008的  JDBC里的  sqljdbc.jar放到了  jdk的lib文件夹下面为什么连不上呢 


import java.sql.*;

public class Test {

public static void main(String[] srg) {

  String driverName = "com.microsoft.sqlserver.jdbc.SQLServerDriver";  //加载JDBC驱动

  String dbURL = "jdbc:sqlserver://localhost:8080; DatabaseName=electricsystem";  //连

接服务器和数据库sample

  String userName = "sa"; 
  String userPwd = "123"; 
  Connection dbConn;


  try {

  Class.forName(driverName);

  dbConn = DriverManager.getConnection(dbURL, userName, userPwd);

  System.out.println("Connection Successful!");  //如果连接成功控制台输出Connection

Successful!

  } catch (Exception e) {

  e.printStackTrace();

  }

}

}
********************************************
错误信息
********************************************
java.lang.ClassNotFoundException: com.microsoft.sqlserver.jdbc.SQLServerDriver
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassL