如何避免嵌套事务不支持的错误？

Z时代
2024-01-10
分类：问答

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关闭了会话，但是有时我的代码遇到以下错误，但是当我几次执行相同的操作时，它会超过错误并可以正常工作。

我的hibernate状态是4.2.1。

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

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

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();
    }
  }
}

<?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>

回答：

在您的“我的代码”代码段中，可能存在一些问题：

发生异常时，没有finally阻止关闭会话的块

您正在打电话session.close()，但这与有所不同HibernateUtils.closeSession()。因此，ThreadLocal不会清除。

没有catch例外。结果是没有rollback。

您是抛出异常还是被（静默）忽略？

如果之后的“待办事项”块中有异常begin()，则事务保持打开状态，并且ThreadLocal不清除。

您的代码可能正常工作，但是在高负载下可能会发生（SQL锁定）超时等情况，在这种情况下，偶尔会抛出异常。

因此，请检查每个代码段以进行 正确的 异常处理：

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();
}