Thanks,
this change bypass the "Large Objects' Error
but I currently encounter another issue about "JPA, @Lob and PostgreSQL oid", I mean with the JPA, what the 'workItemByteArray' returned actually is the oid bytearray, but not the raw content data bytearray, i'm still investigate on it..
some reference:
[1] http://virgo47.wordpress.com/2008/06/13/jpa-postgresql-and-bytea-vs-oid-type/
[2] http://jdbc.postgresql.org/documentation/publicapi/org/postgresql/largeobject/LargeObjectManager.html
[3] http://snipplr.com/view/53917/postgres-how-to-read-oid-value-using-jdbc-api/
the bottom line is, use the PostgreSQL JDBC driver to access the real data bytearray with oid, i think