Spring aop与HibernateTemplate——session管理（每事务一次 Session）
一、HibernateTemplate与Spring aop简介
参见http://bbs.csdn.net/topics/340207475中网友blueram的发言。（感谢blueram）
二、在网友blueram有一句话是本文讲述的主题：
“更优秀的 Session 管理机制。 Spring 提供"每事务一次 Session" 的机制，该机制能大大提高了系统性能，而且 Spring 对 Session 的管理是透明的，无须在代码中操作 Session。”——举例说明：
HibernateTemplate有一个saveOrUpdate方法，该方法用于保存或更新数据，且执行一次即关闭session，这样无法在同一session中添加两条或以上的数据，但若在spring的配置文件中对hirbernate进行事务管理（aop），则可避免这一问题，下面进行代码说明。
三、Spring aop与HibernateTemplate——session管理（每事务一次 Session）
1.在测试类中测试“利用HibernateTemplate在同一session中添加两条数据”。测试结果：fail
注：这里测试的表涉及三个：STUDENT，TEACHER，TEACHER_STUDENT。表STUDENT与表TEACHER呈多对多关联，TEACHER_STUDENT为中间表。
代码：
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:spring.xml")
public class Many2ManyTest {
@Resource
private HibernateTemplate hibernateTemplate;
@Resource
private SessionFactory sessionFactory;
@Resource
private Many2ManyService many2ManyService;
@Test//fail
public void add0(){
Set<Teacher> ts = new HashSet<Teacher>();
Teacher t1 = new Teacher();
t1.setName("t1");
ts.add(t1);
Teacher t2 = new Teacher();
t2.setName("t2");
ts.add(t2);
Set<Student> ss = new HashSet<Student>();
Student s1 = new Student();
s1.setName("s1");
ss.add(s1);
Student s2 = new Student();
s2.setName("s2");
ss.add(s2);
t1.setStudents(ss);
t2.setStudents(ss);
hibernateTemplate.saveOrUpdate(t1);
hibernateTemplate.saveOrUpdate(t2);
hibernateTemplate.saveOrUpdate(s1);
hibernateTemplate.saveOrUpdate(s2);
}
}
运行，出现异常，异常信息如下：
org.springframework.dao.InvalidDataAccessApiUsageException: object references an unsaved transient instance - save the transient instance before flushing: com.chen.vo.Student; nested exception is org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.chen.vo.Student
at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:671)
at org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:412)
at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:411)
at org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
at org.springframework.orm.hibernate3.HibernateTemplate.saveOrUpdate(HibernateTemplate.java:737)
at com.chen.test.Many2ManyTest.add0(Many2ManyTest.java:56)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:232)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:175)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.chen.vo.Student
at org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:242)
at org.hibernate.type.EntityType.getIdentifier(EntityType.java:430)
at org.hibernate.type.ManyToOneType.nullSafeSet(ManyToOneType.java:101)
at org.hibernate.persister.collection.AbstractCollectionPersister.writeElement(AbstractCollectionPersister.java:777)
at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1165)
at org.hibernate.action.CollectionRecreateAction.execute(CollectionRecreateAction.java:58)
at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:279)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:263)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:171)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1028)
at org.springframework.orm.hibernate3.HibernateAccessor.flushIfNecessary(HibernateAccessor.java:390)
at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:407)
... 31 more
分析：当前的事务需求是在同一session中添加两个老师，两个学生以及他们关联的中间数据，然后同步至数据库。而异常信息“save the transient instance before flushing”表明在同步数据库之前已经保存了数据（transient instance）--这个数据就是t1。在数据库中查询表TEACHER，结果如下：
这一结果印证了上述异常——简单地说session添加t1就关闭了，无法再继续添加t2，s1，s2。
当然，这里有替代方法，即利用hibernate的原生session采用编程式事务：
代码：
@Test//success
public void add01(){
Session s = null;
Transaction tx = null;
Set<Teacher> ts = new HashSet<Teacher>();
Teacher t1 = new Teacher();
t1.setName("t1");
ts.add(t1);
Teacher t2 = new Teacher();
t2.setName("t2");
ts.add(t2);
Set<Student> ss = new HashSet<Student>();
Student s1 = new Student();
s1.setName("s1");
ss.add(s1);
Student s2 = new Student();
s2.setName("s2");
ss.add(s2);
t1.setStudents(ss);
t2.setStudents(ss);
SessionFactory sessionFactory = hibernateTemplate.getSessionFactory();
s = sessionFactory.openSession();
tx = s.beginTransaction();
s.saveOrUpdate(t1);
s.saveOrUpdate(t2);
s.saveOrUpdate(s1);
s.saveOrUpdate(s2);
tx.commit();
s.close();
}
运行，Hibernate处理的SQL：
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into Teacher (name, id) values (?, ?)
Hibernate: insert into Teacher (name, id) values (?, ?)
Hibernate: insert into Student (name, id) values (?, ?)
Hibernate: insert into Student (name, id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
以上SQL表明Hibernate已同步至数据库8条数据，分别是：向表Teacher添加了t1，t1，向表Student添加了s1，s2，向表teacher_student添加了4条级联数据。
在数据库中查询，结果如下：
可以看出，已添加了8条数据。
上述方法虽然解决了问题，但这种事务管理方式并非理想方式，采用Spring 的aop对Hibernate进行事务管理是一个很好的方式，下面进行介绍。
2.采用Spring 的aop对Hibernate进行事务管理
Spring的有关aop的配置信息如下：
<bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory" ref="sessionFactory"></property>
</bean>
<aop:config>
<aop:pointcut expression="execution(* com.chen.service.*.*(..))" id="managerOperation"/>
<aop:advisor advice-ref="txAdvice" pointcut-ref="managerOperation"/>
</aop:config>
<tx:advice id="txAdvice" transaction-manager="transactionManager">
<tx:attributes>
<tx:method name="*" propagation="REQUIRED" read-only="true"/>
<tx:method name="save*" propagation="REQUIRED" />
<tx:method name="del*" propagation="REQUIRED" />
</tx:attributes>
</tx:advice>
从上述配置信息可以得知事务管理的类限定在com.chen.service这个包中，现在在这个包中新建一个类：Many2ManyService，添加一个saveOrUpdate方法，将测试类中add0方法中的代码copy其中。
代码：
package com.chen.service;
import java.util.HashSet;
import java.util.Set;
import javax.annotation.Resource;
import org.springframework.orm.hibernate3.HibernateTemplate;
import org.springframework.stereotype.Service;
import com.chen.vo.Student;
import com.chen.vo.Teacher;
@Service("many2ManyService")
public class Many2ManyService {
@Resource
private HibernateTemplate hibernateTemplate;
public void saveOrUpdate(){
Set<Teacher> ts = new HashSet<Teacher>();
Teacher t1 = new Teacher();
t1.setName("t1");
ts.add(t1);
Teacher t2 = new Teacher();
t2.setName("t2");
ts.add(t2);
Set<Student> ss = new HashSet<Student>();
Student s1 = new Student();
s1.setName("s1");
ss.add(s1);
Student s2 = new Student();
s2.setName("s2");
ss.add(s2);
t1.setStudents(ss);
t2.setStudents(ss);
hibernateTemplate.saveOrUpdate(t1);
hibernateTemplate.saveOrUpdate(t2);
hibernateTemplate.saveOrUpdate(s1);
hibernateTemplate.saveOrUpdate(s2);
}
}
在测试类中测试此方法：
代码：
@Test
public void add02(){
many2ManyService.saveOrUpdate();
}
运行（注：运行此方法前已清空之前添加的8条数据），Hibernate处理的SQL：
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: select hibernate_sequence.nextval from dual
Hibernate: insert into Teacher (name, id) values (?, ?)
Hibernate: insert into Teacher (name, id) values (?, ?)
Hibernate: insert into Student (name, id) values (?, ?)
Hibernate: insert into Student (name, id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
Hibernate: insert into teacher_student (teacher_id, student_id) values (?, ?)
以上SQL表明Hibernate已同步至数据库8条数据，分别是：向表Teacher添加了t1，t1，向表Student添加了s1，s2，向表teacher_student添加了4条级联数据。至此，可以小结：在saveOrUpdate方法中连续执行hibernateTemplate的4个saveOrUpdate方法均处于同一session中，等到添加最后一条数据，session才关闭，而不会像在测试类中的add0方法那样只执行一条saveOrUpdate方法后立即关闭。
在数据库中查询，结果如下：
可以看出，已添加了8条数据。
小结：采用Spring aop对Hibernate进行事务管理后，无须在代码中操作 Session，不仅提高了系统性能，且可将事务管理逻辑与代码分离，使事务可在全局事务和局部事务之间切换。
