为什么MySQL的root用户的密码为空可以成功连接,设置密码以后即出错? 出错信息如下: java.sql.SQLException: Communication failure during handshake. Is there a server running on localhost:3306? at org.gjt.mm.mysql.MysqlIO.init(MysqlIO.java:327) at org.gjt.mm.mysql.Connection.connectionInit(Connection.java:261) at org.gjt.mm.mysql.jdbc2.Connection.connectionInit(Connection.java:89) at org.gjt.mm.mysql.Driver.connect(Driver.java:167) at java.sql.DriverManager.getConnection(DriverManager.java:523)