如何避免嵌套事务不支持错误？

Question

我需要确保许多并发用户能够访问数据库.虽然在每次提交后我都会关闭会话,但有时我的代码会遇到以下错误,但是当我执行相同的操作几次时,它会超过错误并起作用.

我的休眠是4.2.1.Final

Messages:   
nested transactions not supported
File:   org/hibernate/engine/transaction/spi/AbstractTransactionImpl.java
Line number:    152

我的守则

session = HibernateUtil.getSession();
session.getTransaction().begin();       OR session.beginTransaction();
       ...   to do ....
session.getTransaction().commit();
session.close();                        OR HibernateUtil.closeSession();

的HibernateUtil

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;

public class HibernateUtil {

   private static ServiceRegistry serviceRegistry;
   private static final ThreadLocal<Session> threadLocal = new ThreadLocal();
   private static SessionFactory sessionFactory;
    private static SessionFactory configureSessionFactory() {
        try {

            Configuration configuration = new Configuration();
            configuration.configure();
            serviceRegistry = new ServiceRegistryBuilder()
                                 .applySettings(configuration.getProperties())
                                 .buildServiceRegistry();
            sessionFactory = configuration.buildSessionFactory(serviceRegistry);

            return sessionFactory;
        } catch (HibernateException e) {
            System.out.append("** Exception in SessionFactory **");
            e.printStackTrace();
        }
       return sessionFactory;
  }


  static {
    try {
      sessionFactory = configureSessionFactory();
    } catch (Exception e) {
      System.err.println("%%%% Error Creating SessionFactory %%%%");
      e.printStackTrace();
    }
  }

  private HibernateUtil() {
  }

  public static SessionFactory getSessionFactory() {
    return sessionFactory;
  }

  public static Session getSession() throws HibernateException {
    Session session = threadLocal.get();

    if (session == null || !session.isOpen()) {
      if (sessionFactory == null) {
        rebuildSessionFactory();
      }
      session = (sessionFactory != null) ? sessionFactory.openSession() : null;
      threadLocal.set(session);
    }

    return session;
  }

  public static void rebuildSessionFactory() {
    try {
      sessionFactory = configureSessionFactory();
    } catch (Exception e) {
      System.err.println("%%%% Error Creating SessionFactory %%%%");
      e.printStackTrace();
    }
  }

  public static void closeSession() throws HibernateException {
    Session session = (Session) threadLocal.get();
    threadLocal.set(null);

    if (session != null) {
      session.close();
    }
  }
}

组态

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <!-- Database connection settings -->
        <property name="connection.driver_class">
            com.mysql.jdbc.Driver
        </property>
        <property name="connection.url">
            jdbc:mysql://localhost:3306/MyProject
        </property>
        <property name="connection.username">root</property>
        <property name="connection.password"></property>

        <!-- JDBC connection pool (use the built-in) -->
        <property name="connection.pool_size">12</property>

        <!-- SQL dialect -->
        <property name="dialect">
            org.hibernate.dialect.MySQLDialect
        </property>

        <!-- Enable Hibernate's automatic session context management -->
        <property name="current_session_context_class">thread</property>

        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">
            org.hibernate.cache.NoCacheProvider
        </property>

        <!-- Echo all executed SQL to stdout -->
        <property name="show_sql">true</property>

                <mapping class="com.project.common.Project" />
                <mapping class="com.project.common.School" />
                <mapping class="com.project.common.Address" />
                <mapping class="com.project.common.Female" />
                <mapping class="com.project.common.Male" />
                <mapping class="com.project.common.Credential" />
                <mapping class="com.project.common.Users" />

    </session-factory>

</hibernate-configuration>

Answer 1

在"我的代码"代码段中,可能存在一些问题:

1. 如果发生异常,则无法finally关闭会话
2. 你在呼唤session.close(),但这与之不同HibernateUtils.closeSession().所以ThreadLocal没有清除.
3. catch例外没有阻止; 因此没有rollback.
4. 你是否重新抛出异常或是否(无声地)被忽略？

如果之后"待办事项"块中存在异常begin(),则事务保持打开状态,并且ThreadLocal不会被清除.

您的代码可能正常工作,但在高负载下可能会有(SQL锁定)超时等,在这种情况下,偶尔会抛出异常.

因此,请检查每个代码段是否正确处理异常:

final Session session = HibernateUtil.getSession();
try {
  final Transaction transaction = session.beginTransaction();
  try {
    // The real work is here
    transaction.commit();
  } catch (Exception ex) {
    // Log the exception here
    transaction.rollback();
    throw ex;
  }
} finally {
  HibernatilUtil.closeSession();
}

您可以添加一些"簿记"代码HibernateUtil.getSession()和HibernateUtil.closeSession():记录每个访问,包括线程的名称.最终,同一个线程中的一个或多个"获取"必须后跟"关闭".

在你的情况下,我甚至会考虑只有一个"获取",并且只要你的线程正在执行其工作单元就通过会话:这样可能更容易找到问题.

还有一个关于SO的问题报告了类似的问题:Hibernate 4.1.9(最新的最终版本)报告不支持嵌套事务.

commit()如果事务已经完成(通过调用wasCommitted()),您可以在检查后添加一些代码.

来自Javadoc的引用wasCommitted():

即使在成功调用commit()之后,此方法也可能返回false.例如,如果没有启动事务,基于JTA的策略会在commit()上调用no-op; 在这种情况下,他们还将wasCommitted()报告为false.

Answer 2

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:

Transaction transaction = null;
    try {
      session = HibernateUtil.getSession();
      transaction  = session.beginTransaction();
       ...   to do ....
      transaction.commit();
    }
    catch (RuntimeException e) {
        transaction.rollback();
        throw e;
    }

在Hibernate.cfg.xml中添加以下属性

 <prop key="hibernate.current_session_context_class">thread</prop>

Answer 3

在代码中使用session.beginTransaction()而不是session.getTransaction().begin().您需要开始一个新的工作单元,因此beginTransaction将开始一个新的事务.所以你的代码看起来像:

session = HibernateUtil.getSession();
Transaction transaction = session.beginTransaction();
       ...   to do ....
transaction.commit();

单击此处获取有关beginTransaction()的更多信息; 方法.

我认为这将解决您的问题.如果问题仍然存在,请告诉我.