Hibernate javax.persistence.RollbackException：提交事务时出错
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Hibernate javax.persistence.RollbackException: Error while committing the transaction
提问by user3159152
I am developing a java web application using Hibernate and MySQL. Sometimes when I try to persist things, I get this rollback exception:
我正在使用 Hibernate 和 MySQL 开发一个 java web 应用程序。有时，当我尝试坚持操作时，我会收到此回滚异常：
javax.persistence.RollbackException: Error while committing the transaction
at org.hibernate.jpa.internal.TransactionImpl.commit(TransactionImpl.java:94)
at com.tulips.dao.CommentDao.saveOrUpdate(CommentDao.java:42)
at com.tulips.servlets.CommentsServlet.doPost(CommentsServlet.java:168)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at org.hibernate.event.internal.AbstractFlushingEventListener.prepareEntityFlushes(AbstractFlushingEventListener.java:155)
at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:91)
at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:55)
at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1222)
at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:425)
at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:177)
at org.hibernate.jpa.internal.TransactionImpl.commit(TransactionImpl.java:77)
... 23 more
here is my persistence.xml file :
这是我的 persistence.xml 文件：
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="licenta_pu"
transaction-type="RESOURCE_LOCAL">
<!-- <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider> -->
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/tulips"/>
<property name="hibernate.connection.username" value="...." />
<property name="hibernate.connection.password" value="...." />
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>
<property name="hibernate.show-sql" value="false" />
<!-- <property name="hibernate.jdbc.batch_size" value="1000" /> -->
<!-- <property name="hibernate.hbm2ddl.auto" value="update" /> -->
</properties>
</persistence-unit>
</persistence>
I've tried changing the hibernate provider but that didn't help :( [org.hibernate.ejb.HibernatePersistence and org.hibernate.jpa.HibernatePersistenceProvider]
我试过更改休眠提供程序，但这没有帮助:( [org.hibernate.ejb.HibernatePersistence 和 org.hibernate.jpa.HibernatePersistenceProvider]
I don't know exactly how to replicate this error, sometimes I get it, sometimes I don't. I have observed that every time after I restart my computer and run the project in Eclipse, and try to persist data, it works. If I stop the project, eventually add some data into the database via MySQL Workbench, and then run the project again, I get the error.
我不知道如何复制这个错误，有时我明白，有时我不明白。我观察到每次在我重新启动计算机并在 Eclipse 中运行项目并尝试保留数据后，它都可以工作。如果我停止该项目，最终通过 MySQL Workbench 将一些数据添加到数据库中，然后再次运行该项目，则会出现错误。
Here is my EntityManagerHolder:
这是我的 EntityManagerHolder：
public class EntityManagerHolder {
private static EntityManagerHolder INSTANCE = new EntityManagerHolder();
private EntityManagerFactory emf;
private EntityManager entityManager;
public EntityManager getEntityManager() {
return entityManager;
}
public static EntityManagerHolder getInstance() {
return INSTANCE;
}
private EntityManagerHolder() {
super();
emf = Persistence
.createEntityManagerFactory("licenta_pu");
entityManager = emf.createEntityManager();
}
}
Here is my GenericDao:
这是我的 GenericDao：
import javax.persistence.EntityManager;
import javax.transaction.Transactional;
import com.tulips.model.AbstractEntity;
@Transactional
public abstract class GenericDao {
protected EntityManager em;
public GenericDao(EntityManager em) {
this.em = em;
}
public void saveOrUpdate(AbstractEntity e) {
if (e == null) {
throw new NullPointerException("Trying to persist a null object");
}
em.getTransaction().begin();
if (e.getId() == null) {
em.persist(e);
} else {
em.merge(e);
}
em.getTransaction().commit();
}
}
I'm using the following Hibernate libraries:
我正在使用以下 Hibernate 库：
mysql-connector-java-5.1.9.jar;
hibernate-commons-annotations-4.0.4.Final.jar;
hibernate-core-4.3.4.Final.jar;
hibernate-entitymanager-4.3.4.Final.jar;
hibernate-jpa-2.1-api-1.0.0.Final.jar;
采纳答案by David Levesque
The problem might be that you have a single EntityManager shared by all Web requests. EntityManager is not thread safe. The standard approach in a webapp is to create a new instance of EntityManager for each request. It is ok to have a shared EntityManagerFactory, but not a shared EntityManager.
问题可能是您有一个由所有 Web 请求共享的 EntityManager。EntityManager 不是线程安全的。webapp 中的标准方法是为每个请求创建一个新的 EntityManager 实例。可以共享 EntityManagerFactory，但不能共享 EntityManager。
From the Hibernate doc:
从休眠文档：
An EntityManager is an inexpensive, non-threadsafe object that should be used once, for a single business process, a single unit of work, and then discarded. An EntityManager will not obtain a JDBC Connection (or a Datasource) unless it is needed, so you may safely open and close an EntityManager even if you are not sure that data access will be needed to serve a particular request.
EntityManager 是一个廉价的、非线程安全的对象，应该为单个业务流程、单个工作单元使用一次，然后丢弃。除非需要，否则 EntityManager 不会获得 JDBC 连接（或数据源），因此即使您不确定是否需要数据访问来服务特定请求，您也可以安全地打开和关闭 EntityManager。
