mysql连接tomcat - Java / Web 开发

我已经按照教程上配置tomcat的server.xml
<Context path = "/POS" docBase = "POS" debug = "5" reloadable = "true" crossContext = "true" workDir = "">
  <Resource name = "jdbc/pos" auth = "Container" type = "javax.sql.DataSource" maxActive = "100" maxIdle ="30" maxWait = "10000"
  username = "root" password = "rarzyz" driverClassName = "org.gjt.mm.mysql.Driver" url = "jdbc:mysql:// localhost/test"/>
  </Context>

也把教程光盘上的web.xml和appcontext.xml都复制去了。但是还是在按提交登陆的用户名和密码页面后，显示http status 500 The server encountered an internal error () that prevented it from fulfilling this request.

org.hibernate.exception.GenericJDBCException: Cannot open connection
这个不能打开连接提示，是不是提示我的出错了啊。我看过tomcat和mysql服务我都开了。郁闷啊。驱动我也考到lib里面了。实在不知道错误在哪里了

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貌似这两个都有问题：
driverClassName = "org.gjt.mm.mysql.Driver" url = "jdbc:mysql:// localhost/test"/> 
驱动名不对，url少了端口号。。。

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public static String driver="com.mysql.jdbc.Driver"
public static String url="jdbc:mysql://localhost/mydata?user=用户名&password=密码" 

可以不要端口号

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