ORA-12519, TNS: не найден соответствующий обработчик службы при вставке в базу данных Oracle с X потоками

Я пытаюсь вставить в базу данных Oracle, которая имеет две колонки-

ID         Primary Key     varchar2 (4000)
ACCOUNT                    varchar2 (4000)

я написал многопоточную программу для этого. И каждый поток использует unique id каждый раз вставлять в ID column as ID - это первичный ключ.

единственная проблема, с которой я столкнулся в какой-то момент - тем ниже код, бросает следующее исключение после запуска в течение нескольких секунд.

 1) Null Pointer Exception
 2) java.sql.SQLException: Listener refused the connection with the following error:ORA-12519, TNS:no appropriate service handler found

Я не могу найти причину этой проблемы в моем коде, как все по-моему, неплохо. Поскольку я закрываю каждое соединение должным образом. Тогда как этот NPE выбрасывается и другое исключение?

    ExecutorService service = Executors.newFixedThreadPool(10);

    try {
        // queue some tasks
        for (int i = 0; i < 100 * 10; i++) {
            service.submit(new ThreadTask());
        }
        service.shutdown();
        service.awaitTermination(Long.MAX_VALUE, TimeUnit.SECONDS);

        while (!service.isTerminated()) {

        }
    } catch (InterruptedException e) {
        LOG.warn("Threw a Interrupted Exception in" + XMPLoadTest.class.getSimpleName()
                + ".XMPLoadTest: boss told me to stop...Not my fault!!");
    }

ниже приведен класс ThreadTask -

class ThreadTask implements Runnable {

    private static final String DRIVER = "oracle.jdbc.driver.OracleDriver";
    private static final String CONNECTION = "jdbc:oracle:thin:@localhost:1521:ORCL";
    private static final String USER = "scott";
    private static final String PASSWORD = "tiger";
    private static Connection dbConnection = null;
    private static PreparedStatement preparedStatement = null;

    private static final AtomicInteger id = new AtomicInteger(1);

    private final static Logger LOG = Logger.getLogger(ThreadTask.class.getName());

    public ThreadTask() {

    }

    @Override
    public void run() {

        try {

            dbConnection = getDBConnection();
            preparedStatement = dbConnection.prepareStatement(Constants.INSERT_ORACLE_SQL);

            preparedStatement.setString(1, String.valueOf(id.getAndIncrement()));
            preparedStatement.setString(2, Constants.A_ACCOUNT);

            preparedStatement.executeUpdate();

        } catch (Exception e) {
            // NPE getting thrown here/And second exception as well
            LOG.error("Threw a SQLException in " + getClass().getSimpleName(), e);
        } finally {
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                    preparedStatement = null;
                } catch (SQLException e) {
                    //Oouch...
                    LOG.error("Threw a SQLException in finally block of prepared statement " + getClass().getSimpleName(), e);
                }
            }
            if (dbConnection != null) {
                try {
                    dbConnection.close();
                    dbConnection = null;
                } catch (SQLException e) {
                    //Better go and look for SQL.
                    LOG.error("Threw a SQLException in finally block of dbConnection " + getClass().getSimpleName(), e);
                }
            }
        }
    }

    /**
     * Attempts to establish a connection to the given database URL
     * 
     * @return the db connection
     */
    private Connection getDBConnection() {

        Connection dbConnection = null;

        try {
            Class.forName(XMP_DRIVER);
            dbConnection = DriverManager.getConnection(CONNECTION, USER, PASSWORD);
        } catch (ClassNotFoundException e) {
            LOG.error("Threw a ClassNotFoundException in " + getClass().getSimpleName(), e);
        } catch (SQLException e) {
            //DAMN! I'm not....
            LOG.error("Threw a SQLException in " + getClass().getSimpleName(), e);
        } catch (Exception e) {
            LOG.error("Threw a Exception in " + getClass().getSimpleName(), e);
        }

        return dbConnection;
    }
}

есть ли потенциальные проблемы с моим код? Я больше беспокоюсь об этом NPE.

StackTrace:

19:14:28,372 ERROR ThreadTask:187 - Threw a SQLException in ThreadTask
java.sql.SQLException: Listener refused the connection with the following error:
ORA-12519, TNS:no appropriate service handler found

    at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:458)
    at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:546)
    at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:236)
    at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:32)
    at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:521)
    at java.sql.DriverManager.getConnection(DriverManager.java:322)
    at java.sql.DriverManager.getConnection(DriverManager.java:358)
    at com.ebay.xmp.lnp.ThreadTask.getDBConnection(XMPLoadTest.java:179)
    at com.ebay.xmp.lnp.ThreadTask.run(XMPLoadTest.java:137)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:452)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:314)
    at java.util.concurrent.FutureTask.run(FutureTask.java:149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:897)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:919)
    at java.lang.Thread.run(Thread.java:736)
Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error:
ORA-12519, TNS:no appropriate service handler found

    at oracle.net.ns.NSProtocol.connect(NSProtocol.java:395)
    at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1102)
    at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:320)
    ... 14 more
19:14:28,376 ERROR ThreadTask:139 - Threw a SQLException in ThreadTask
java.lang.NullPointerException
    at com.ebay.xmp.lnp.ThreadTask.run(XMPLoadTest.java:137)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:452)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:314)
    at java.util.concurrent.FutureTask.run(FutureTask.java:149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:897)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:919)
    at java.lang.Thread.run(Thread.java:736)