Recently,there'r lot of errors below showed in the weblogic log.at the same time, there'r a lot of INACTIVE session generated in the oracle DB's v$session table .
But the system shows normal.
<2013/02/19 10:00:00 CST> <Error> <JDBC> <zjq51101> <coo011> <[ACTIVE] ExecuteThread: '127' for queue: 'weblogic.kernel.Default (self-tuning)'> <<anonymous>> <> <ce9d41a710a949eb:2e7eb449:13c8050d3d2:-8000-00000000001268ce> <1361255772945> <BEA-001112><Test "SELECT 1 FROM DUAL" set up for pool "DS_Coo01" failed with exception: "java.lang.NullPointerException".>
Is the database up and running when you started weblogic server?
Weblogic server executes default SQL "SELECT 1 FROM DUAL " to test the connectivity to Database configured in Weblogic Server data sources and to initialize the connections and to add it to the Connection Pool.
You may see the errors if weblogic is unable to initialize the connections or unable to connect to DB to execute the default SQL Statement.