解决连接Oracle时出现的异常

异常现象如下：
java.sql.SQLException: Io 异常: Connection refused(DESCRIPTION=(TMP=)(VSNNUM=169870336)(ERR=12505)(ERROR_STACK=(ERROR=(CODE=12505)(EMFI=4))))
    at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:134)
    at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:179)
    at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:334)
    at oracle.jdbc.ttc7.TTC7Protocol.handleIOException(TTC7Protocol.java:3695)
    at oracle.jdbc.ttc7.TTC7Protocol.logon(TTC7Protocol.java:352)
    at oracle.jdbc.driver.OracleConnection.<init>(OracleConnection.java:362)
    at oracle.jdbc.driver.OracleDriver.getConnectionInstance(OracleDriver.java:536)
    at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:328)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
 ...
原因一般为jdbc连接URL里面填写了错误的sid，查看sid方法如下：
select INSTANCE_NAME from v$instance;
然后填写正确的sid即可。