环境：Oracle 11g R2 + PL SQL Developer + SQL Plus

        问题：Oracle主服务和监听器服务已经启动，使用SQL Plus能够正常连接，使用PL SQL Developer连接报次错误：ORA-12514: TNS: 监听程序当前无法识别连接描述符中请求的服务。如图：

         解决：

         打开H:\Oracle\product\11.2.0\dbhome_1\NETWORK\ADMIN（不同机器目录可能不同）目录下的listener.ora文件，发现此文件内容如下：

#listener.ora Network Configuration File:
H:\Oracle\product\11.2.0\dbhome_1\network\admin\listener.ora
#Generated by Oracle configuration tools.
 
SID_LIST_LISTENER=
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME =H:\Oracle\product\11.2.0\dbhome_1)
      (PROGRAM = extproc)
      (ENVS ="EXTPROC_DLLS=ONLY:H:\Oracle\product\11.2.0\dbhome_1\bin\oraclr11.dll")
    )
  )
 
LISTENER=
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY =EXTPROC1521))
      (ADDRESS = (PROTOCOL = TCP)(HOST =localhost)(PORT = 1521))
    )
  )
 
ADR_BASE_LISTENER= H:\Oracle

修改成如下内容（注意红色部分的内容）：

#listener.ora Network Configuration File:

H:\Oracle\product\11.2.0\dbhome_1\network\admin\listener.ora

#Generated by Oracle configuration tools.

SID_LIST_LISTENER=

  (SID_LIST =

         (SID_DESC =

      (GLOBAL_DBNAME = ORCL)

      (ORACLE_HOME =H:\Oracle\product\11.2.0\dbhome_1)

      (SID_NAME = ORCL)

    )

    (SID_DESC =

      (SID_NAME = CLRExtProc)

      (ORACLE_HOME = H:\Oracle\product\11.2.0\dbhome_1)

      (PROGRAM = extproc)

      (ENVS ="EXTPROC_DLLS=ONLY:H:\Oracle\product\11.2.0\dbhome_1\bin\oraclr11.dll")

    )

  )

LISTENER=

  (DESCRIPTION_LIST =

    (DESCRIPTION =