ORA-12516, TNS:listener could not find available handler with matching protocol stack

java.sql.SQLException: Listener refused the connection with the following error:
ORA-12516, TNS:listener could not find available handler with matching protocol stack

at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:743)
at oracle.jdbc.driver.PhysicalConnection.connect(PhysicalConnection.java:662)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:560)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
...
...
...
Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error:
ORA-12516, TNS:listener could not find available handler with matching protocol stack

at oracle.net.ns.NSProtocolStream.negotiateConnection(NSProtocolStream.java:275)
at oracle.net.ns.NSProtocol.connect(NSProtocol.java:264)
at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1452)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:496)
... 8 more
java.sql.SQLException: Listener refused the connection with the following error:
ORA-12516, TNS:listener could not find available handler with matching protocol stack

at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:743)
at oracle.jdbc.driver.PhysicalConnection.connect(PhysicalConnection.java:662)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:560)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:185)
...
...
...
Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error:
ORA-12516, TNS:listener could not find available handler with matching protocol stack

at oracle.net.ns.NSProtocolStream.negotiateConnection(NSProtocolStream.java:275)
at oracle.net.ns.NSProtocol.connect(NSProtocol.java:264)
at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1452)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:496)
... 8 more

参考：alter system set processes=300 scope=spfile;

alter system set sessions=300 scope=spfile;
http://www.dba-oracle.com/t_ora_12516-tns_ould_not_find_available_handler.htm
    
http://stackoverflow.com/questions/20742794/ora-12516-tnslistener-could-not-find-available-handler
执行以下命令，登记oracle服务，问题得到解决.

alter system set processes=300 scope=spfile;
alter system set sessions=300 scope=spfile;