如何使用entityManager在JPA中启动事务

Question

我已经开始开发一个使用spring、hibernate、JPA、SOAP webservices的应用程序。现在有一个要求，即必须在事务中运行某些查询。如果其中任何一个失败，整个事务都应该回滚。

dao层的代码如下：

import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;
import javax.persistence.PersistenceContext;
import javax.persistence.PersistenceContextType;
import javax.persistence.Query;
import org.hibernate.Session;

    public class BillDAOImpl implements BillDao{

             @PersistenceContext(type = PersistenceContextType.EXTENDED)
             private EntityManager em;

             public boolean processBills() throws Exception{

             EntityTransaction tx = null;
             Session session = null;

             try{

                 session = em.unwrap(Session.class);
                 tx = em.getTransaction();

                 Bill bill = em.find(Bill.class, billId);

                 //session.beginTransaction();
                 tx.begin();
                 ...
                 ...
                 em.persist(bill);
                 ...
                 ...
                 em.merge(<other object>);
                 ...
                 ...
                 //session.getTransaction().commit();
                 tx.commit();
             } catch(){
             }

             }

    }

当它执行tx = em.getTransaction()时，它会给出以下错误：

java.lang.IllegalStateException: Cannot execute getTransaction() on a container-managed EntityManager

其他与事务相关的属性如下：

<bean id="tuneEntityManagerFactory"
        class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
        p:persistenceXmlLocation="classpath*:META-INF/tune-persistence.xml"
        p:persistenceUnitName="tunePersistenceUnit" p:loadTimeWeaver-ref="loadTimeWeaver"
        p:jpaVendorAdapter-ref="jpaVendorAdapter" p:jpaDialect-ref="jpaDialect"
        p:dataSource-ref="tuneDbDataSource">
        <property name="jpaProperties">
            <props>
                <prop key="hibernate.transaction.manager_lookup_class">org.hibernate.transaction.BTMTransactionManagerLookup
                </prop>
                <prop key="net.sf.ehcache.configurationResourceName">/${tune-db.ehcache.config.file}</prop>
                <prop key="hibernate.transaction.flush_before_completion">false</prop>              
                <prop key="hibernate.default_schema">${tune-db.schema}</prop>
                <prop key="org.hibernate.envers.default_schema">${tune-db.schema}</prop>
                <prop key="javax.persistence.validation.mode">${tune-db.data.validation}</prop>
                <prop key="hibernate.connection.isolation">3</prop>
                <prop key="hibernate.connection.release_mode">auto</prop>
                <prop key="hibernate.show_sql">${tune-db.hibernate.show-sql}</prop>
                <prop key="hibernate.format_sql">${tune-db.hibernate.format-sql}</prop>
            </props>
        </property>     
    </bean>

<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="tuneEntityManagerFactory" />
    </bean>

当我使用session.beginTransaction()和session.getTransaction().commit()时，它工作正常。

但是，我想用entityManager中的transaction替换它。那该怎么办呢？

Answer 1

尝试注入EntityManagerFactory，然后手动创建EntityManager：

@PersistenceUnit
private EntityManagerFactory entityManagerFactory;

public boolean processBills() throws Exception{

   EntityManager em = entityManagerFactory.createEntityManager();

   EntityTransaction tx = null;

   Session session = null;

   try{

       session = em.unwrap(Session.class);
       tx = em.getTransaction();

Answer 2

@PersistenceContext返回的EntityManager实例始终是容器管理的EntityManager。容器管理的EntityManager总是JTA EntityManagers，因此它们的生命周期是由容器管理的。我想现在可以理解为什么对它们调用getTransaction()是非法的了。This might help

Answer 3

添加值为true的hibernate.jta.allowTransactionAccess属性，应该允许您手动使用它。尽管混合策略并不是一种好的做法，但让一些代码由JTA管理，一些代码是手动管理的。