多线程访问数据库出现异常(100分)

我在JAVA中多个线程中用JDBC访问ORACLE数据库，老出现诸如bad packet type, bad packet length, Unexpected packet等异常。请大侠们帮忙。

[Wed Aug 27 07:43:23 GMT+08:00 2003] [ERROR][Thread-3] SQL Error: java.sql.SQLException: Io 异常: Unexpected packet:java.sql.SQLException: Io 异常: Unexpected packet
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:134)
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:179)
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:333)
at oracle.jdbc.ttc7.TTC7Protocol.getLobChunkSize(TTC7Protocol.java:2992)
at oracle.sql.LobDBAccessImpl.getChunkSize(LobDBAccessImpl.java:322)
at oracle.sql.BLOB.getChunkSize(BLOB.java:478)
at oracle.sql.BLOB.getBufferSize(BLOB.java:515)
at oracle.sql.BLOB.getBinaryStream(BLOB.java:250)
at com.dbrg.scss.OraPageInfoDAO.select(OraPageInfoDAO.java:268)
at com.dbrg.scss.OraAnalyzerWorkloadDAO.getTask(OraAnalyzerWorkloadDAO.java:251)
at com.dbrg.scss.OraAnalyzerWorkloadDAO.assignWorkload(OraAnalyzerWorkloadDAO.java:75)
at com.dbrg.scss.Analyzer.getWorkload(Analyzer.java:111)
at com.dbrg.scss.AnalyzerWorker.run(AnalyzerWorker.java:106)

[Wed Aug 27 07:43:23 GMT+08:00 2003] [NORMAL][Thread-3] AnalyzerWorker is over because of no workload
[Wed Aug 27 07:43:23 GMT+08:00 2003] [ERROR][Thread-2] SQL Exception: java.sql.SQLException: Io 异常: Bad packet type:java.sql.SQLException: Io 异常: Bad packet type
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:134)
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:179)
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:333)
at oracle.jdbc.driver.OracleResultSetImpl.internal_close(OracleResultSetImpl.java:1466)
at oracle.jdbc.driver.OracleResultSetImpl.next(OracleResultSetImpl.java:251)
at com.dbrg.scss.OraTaskInfoDAO.getKeywordList(OraTaskInfoDAO.java:166)
at com.dbrg.scss.TaskInfo.getKeywordList(TaskInfo.java:170)
at com.dbrg.scss.AnalyzerWorker.parse(AnalyzerWorker.java:163)
at com.dbrg.scss.AnalyzerWorker.processWorkload(AnalyzerWorker.java:132)
at com.dbrg.scss.AnalyzerWorker.run(AnalyzerWorker.java:114)

诸位都没有见过这种问题吗？
我已经将Statement对象都同步了，为什么还老出错？
大家能否谈谈多线程访问数据库的技术吗？