java连接数据库时用url = "jdbc:oracle:thin:@localhost:1521:orcl"或者url = "jdbc:oracle:thin:@127.0.0.1:orcl"时,控制台抛出java.sql.SQLException: Io 异常: The Network Adapter could not establish the connection这样的异常,而把URL中的IP改为自己主机的IP之后又可以用了,这是怎么回事啊?