Cannot get a connection, pool exhausted, cause: ValidateObject failed

連接池突然不能使用了，重啓應用仍然報連接池耗盡，最後debug發現是有人創建了dual表，導致校驗語句select 1 from dual返回值爲空，而無法通過連接池的連接校驗。

Caused by: org.apache.commons.dbcp.SQLNestedException: Cannot get a connection, pool exhausted
    at org.apache.commons.dbcp.PoolingDriver.connect(PoolingDriver.java:183)
    at java.sql.DriverManager.getConnection(DriverManager.java:664)
    at java.sql.DriverManager.getConnection(DriverManager.java:270)
    ... 6 more
Caused by: java.util.NoSuchElementException: Could not create a validated object, cause: ValidateObject failed
    at org.apache.commons.pool.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:871)
    at org.apache.commons.dbcp.PoolingDriver.connect(PoolingDriver.java:175)