ORA-12516 – Possible causes

At least one is when your processes parameter in the database instance(s) has/have been exceeded.

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:451)
        at oracle.jdbc.driver.PhysicalConnection.(PhysicalConnection.java:535)
        at oracle.jdbc.driver.T4CConnection.(T4CConnection.java:218)
        at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:29)
        at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:528)
        at oracle.jdbc.pool.OracleDataSource.getPhysicalConnection(OracleDataSource.java:401)
        at oracle.jdbc.pool.OracleDataSource.getConnection(OracleDataSource.java:288)
        at oracle.jdbc.pool.OracleDataSource.getConnection(OracleDataSource.java:205)
        at stressRetail.run(stressRetail.java:82)
        at java.lang.Thread.run(Unknown Source)
Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error: