总有一种情况，属于那种，代码明明很对，可是就是有意想不到的问题，找半天的bug，然后，关了eclipse 重新开，重新写

  就又对了，问题对的莫名其妙

  连接mysql：

package util;import java.sql.Connection;import java.sql.DriverManager;public class DBHelper {    private static final String driver = "com.mysql.jdbc.Driver";    private static final String url = "jdbc:mysql://localhost:3306/test";    private static final String usernane = "root";    private static final String password = "*****";    private static Connection connection = null;    static    {        try {            Class.forName(driver);        } catch (Exception e) {            e.printStackTrace();        }    }        public  static Connection getConnection() throws Exception    {        if (connection == null) {            connection = DriverManager.getConnection(url,usernane,password);            return connection;        }        return connection;    }        public static void main(String []args)    {        try        {            Connection connection = DBHelper.getConnection();            if (connection!= null) {                System.out.println("数据库连接正常");            }            else            {                System.out.println("数据库连接异常");            }        }catch(Exception e){            e.printStackTrace();        }    }        }