springmvc+hibernate 3.6+jpa 并发时提交事务失败

当多用户同时提交操作，更新数据库时，会出现以下异常。不在并发时，可以提交事务成功。用的entitymanager.lock(entity, LockModeType.PESSIMISTIC_WRITE);engitymanager.lock(entity, LockModeType.PESSIMISTIC_WRITE);同时操作都会出现异常。怎么可以让事务强行提交或提交，不让回滚。谢谢解答
org.springframework.transaction.TransactionSystemException: Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: Transaction marked as rollbackOnly
at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:522)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:755)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:724)
at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:475)
.....
.....
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2430)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2419)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
Caused by: javax.persistence.RollbackException: Transaction marked as rollbackOnly
at org.hibernate.ejb.TransactionImpl.commit(TransactionImpl.java:73)
at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:513)
... 59 more