java.sql.SQLException: No suitable driver

import java.sql.*;
import com.mysql.jdbc.ResultSet;
import com.mysql.jdbc.Statement;
import com.mysql.jdbc.Driver;/**
 *
 * @author Administrator
 */
public class SelectDB {
    
    /** Creates a new instance of SelectDB */
    public static void main(String[] args) {
        try
        {
            Class.forName(" com.mysql.jdbc.Driver");
        }
        catch (java.lang.ClassNotFoundException e)
        {
            System.out.print("Class not found exception occur. Message is:");
            System.out.print(e.getMessage());
        }
        try
        {
            Statement stmt;
            ResultSet rs;
            
            String url = "jdbc:mysql://localhost:3306/DWDM";
            
            String user = "root";
            String passwordofDB = "lm";
            Connection conn = null;
            
            try
            {
                conn = DriverManager.getConnection(url,user,passwordofDB);
            }
            catch(Exception ex)
            {
                ex.printStackTrace();
            }
            
            stmt =(Statement) conn.createStatement();
            rs = (ResultSet) stmt.executeQuery("select* from user");
            
            while (rs.next())
            {
                String id =rs.getString(1);
                String password = rs.getString(2);
                int access=rs.getInt(3);
                String introduction= rs.getString(4);
                
                System.out.println("id:"+id);
                System.out.println("password:"+password);
                System.out.println("access:"+access);
                System.out.println("introduction:"+introduction);
                
            }
            rs.close();
            stmt.close();
            conn.close();
        }
        catch(SQLException e)
        {
            System.out.print("SQL Exception occur.Message is:");
            System.out.print(e.getMessage());
        }
    }
    
}
我mysql的版本是4.1，驱动安装了mysql-connector-java 3.1.7.jar，并且在NetBeans中用数据库管理界面已经连接成功，说明驱动没有错，在类路径中已经.jar文件怎么还会报下面错呢，希望大牛们能指点，跪谢！
java.sql.SQLException: No suitable driver        at java.sql.DriverManager.getConnection(DriverManager.java:532)        at java.sql.DriverManager.getConnection(DriverManager.java:171)        at SelectDB.main(SelectDB.java:44)java.lang.NullPointerException        at SelectDB.main(SelectDB.java:51)Exception in thread "main" Class not found exception occur. Message is: com/mysql/jdbc/Driver