ORA-12514: TNS: 侦听器当前不知道连接描述符中请求的服务

我在尝试通过侦听器连接到 Oracle Database XE 时遇到问题：

 sqlplus system/my_password@XE

我收到以下错误：

ORA-12514: TNS:listener does not currently know of service requested in connect
descriptor

我使用 Ubuntu 12.10 和 Oracle Express Edition 11g。

我的主要目标是将 java + oracle db 与 jdbc 连接，但我得到了同样的错误。

这是我的listener.ora

# listener.ora Network Configuration File:

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = PLSExtProc)
      (ORACLE_HOME = /u01/app/oracle/product/11.2.0/xe)
      (PROGRAM = extproc)
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
      (ADDRESS = (PROTOCOL = TCP)(HOST = watson)(PORT = 1521))
    )
  )

DEFAULT_SERVICE_LISTENER = (XE)

和 tnsnames.ora

# tnsnames.ora Network Configuration File:

XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = watson)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = XE)
    )
  )

EXTPROC_CONNECTION_DATA =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
    )
    (CONNECT_DATA =
      (SID = PLSExtProc)
      (PRESENTATION = RO)
    )
  )

and

lsnrctl service

LSNRCTL for Linux: Version 11.2.0.2.0 - Production on 04-FEB-2014 17:01:44
Copyright (c) 1991, 2011, Oracle.  All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC_FOR_XE)))
Services Summary...
Service "PLSExtProc" has 1 instance(s).
  Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...
    Handler(s):
      "DEDICATED" established:0 refused:0
         LOCAL SERVER
The command completed successfully

我必须在 Windows 服务中重新启动 OracleServiceXE 服务，它又可以正常工作了。