删除时出现"org.hibernate.TransactionException:不支持嵌套事务"错误

Question

运行removeUserFromConference方法时获取此异常:

04/06/2012 00:20:48 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [ConferenceServlet] in context with path [/conf4u] threw exception
org.hibernate.TransactionException: nested transactions not supported
    at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.begin(AbstractTransactionImpl.java:152)
    at org.hibernate.internal.SessionImpl.beginTransaction(SessionImpl.java:1396)
    at sun.reflect.GeneratedMethodAccessor39.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.hibernate.context.internal.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:352)
    at $Proxy12.beginTransaction(Unknown Source)
    at daos.ConferenceDao.isConferenceNameExists(ConferenceDao.java:129)
    at servlets.ConferenceServlet.removeUser(ConferenceServlet.java:232)
    at servlets.ConferenceServlet.processRequest(ConferenceServlet.java:79)
    at servlets.ConferenceServlet.doPost(ConferenceServlet.java:433)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:928)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:987)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:539)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:298)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
04/06/2012 00:27:15 org.apache.catalina.core.StandardContext reload
INFO: Reloading Context with name [/conf4u] has started
04/06/2012 00:27:15 org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc
SEVERE: The web application [/conf4u] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
04/06/2012 00:27:15 org.apache.catalina.core.StandardContext reload
INFO: Reloading Context with name [/conf4u] is completed

道法:

public void removeUserFromConference(Conference conference, User user) {
    ConferencesUsers conferenceUser = getConferenceUser(conference, user);

    Session session = HibernateUtil.getSessionFactory().getCurrentSession();
    session.beginTransaction();

    session.delete(conferenceUser);

    session.getTransaction().commit();
}

模型类:

@Entity
@Table( name = "Conferences_Users" )
public class ConferencesUsers implements Serializable {
    private static final long serialVersionUID = -3401337605668111437L;
    private Conference conference;
    private User user; 
    private int userRole;
    private UserAttendanceStatus attendanceStatus;
    private boolean notifiedByMail;

    ConferencesUsers() {}  //not public on purpose!

    public ConferencesUsers(Conference conf, User user, int userRole) {
         this.conference = conf;
         this.user = user;
         this.userRole = userRole;
         this.attendanceStatus = null;
         this.notifiedByMail = false;
    }

    public ConferencesUsers(Conference conf, User user, int userRole, UserAttendanceStatus attendanceStatus, boolean notifiedByMail) {
         this.conference = conf;
         this.user = user;
         this.userRole = userRole;
         this.attendanceStatus = attendanceStatus;
         this.notifiedByMail = notifiedByMail;
    }

    @Id
    @ManyToOne(cascade = CascadeType.ALL)
    public Conference getConference() {
         return conference;
    }

    public void setConference(Conference conference) {
         this.conference = conference;
    }

    @Id
    @ManyToOne(cascade = CascadeType.ALL)
    public User getUser() {
         return user;
    }

    public void setUser(User user) {
         this.user = user;
    }

    @Enumerated(EnumType.STRING)
    public int getUserRole() {
         return userRole;
    }

    public void setUserRole(int userRole) {
         this.userRole = userRole;
    }

    @Nullable
    public boolean isNotifiedByMail() {
         return notifiedByMail;
    }

    public void setNotifiedByMail(boolean notifiedByMail) {
         this.notifiedByMail = notifiedByMail;
    }

    public UserAttendanceStatus getAttendanceStatus() {
         return attendanceStatus;
    }

    public ConferencesUsers setAttendanceStatus(UserAttendanceStatus attendanceStatus) {
         this.attendanceStatus = attendanceStatus;
         return this;
    }
}

Answer 1

您可能已经开始了一个事务,并尝试在没有提交或回滚前一个事务的情况下开始另一个事务.使用程序化事务划分时的习惯用法如下:

try {
    sess.getTransaction().begin();

    // do some work

    sess.getTransaction().commit()
}
catch (RuntimeException e) {
    sess.getTransaction().rollback();
    throw e;
}

这很麻烦且容易出错,这也是使用EJB或Spring进行声明性事务非常有用的原因之一.

Answer 2

首先,你应该注入hibernateProperties,hibernate.current_session_context_class,

<property name="hibernateProperties">
    <props>
        <prop key="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</prop>
        <prop key="hibernate.show_sql">true</prop>
        <prop key="hibernate.format_sql">true</prop>
        <prop key="hibernate.hbm2ddl.auto">update</prop>
        <prop key="hibernate.current_session_context_class">thread</prop>
    </props>
</property>

然后你可以使用getCurrentSession()来获取CurrentSession.

Session session = sessionFactory.getCurrentSession();
session.beginTransaction();
long count = (Long) session
        .createQuery("select count(*) from User u where u.name = :name")
        .setString("name", name).uniqueResult();
session.getTransaction().commit();