因事务导致hibernate延迟加载出现no session异常的问题排查

文章来源：原创   作者：许秋冬   发布时间：2020-07-03   阅读：5673   标签：源码,事务 分类：spring 专题：我读[不懂]源码

因事务导致hibernate延迟加载出现no session异常

本人对hibernate 的使用不是特别的熟悉,这里只是记录一次帮助同事解决异常排查的过程.
项目中的spring版本为4.1.6
贴出的源码的spring版本为5.1.9

1 项目技术框架

spring + springmvc + hibernate + freemarker

2 异常的产生现象

controller中直接调用serviceA中的方法A 页面可正常渲染;

controller调用serviceB中的方法B, 方法B中调用serviceA中的方法A,渲染页面的时候报异常:no session

3 问题追踪

  1. 根据现象,最直观的原因是session已经关闭, 然后获取懒加载对象的属性的时候,没有获取到session;
  2. 直接调用无错, 但是经过另外一个service调用后就no session, 说明两个session可能并不是一个session
3.1 确认是否是一个session的调试:结果不是一个session;

本项目开启了OpenSessionInViewFilter过滤器,

  1. 断点跟踪OpenSessionInViewFilter中的open的Session, 记录sesson的hashcode—>code1;
  2. 进入serviceB, 通过获取sessionFactory.getCurrentSession(), 记录session的hashcode, 等于code1, 表示此处使用的session是filter中打开的session;
  3. 从serviceB进入serviceA,获取当前session,获得的hashcode值与code1不一致;
3.2 为什么不是一个session: 因为不在一个事物中
  1. 本项目的事务在配置文件中由切面配置;
  2. 由于命名方式的问题,
    1. 入口方法B不要求在事物中运行( propagation=”SUPPORTS”)
    2. 方法A需要在一个事物中运行((propagation=”REQUIRED”))
    3. 导致进入方法B后不需要事务,但是B调用的A方法在事务中运行

关于事务的传播性,小伙伴可自行复习;

3.3 解决问题:修改方法名,保证在一个事务中

修改方法名后, 保证两个方法在一个事务中,再次验证, 两者session一致, 延迟加载的属性可正常加载, 在OpenSessionInViewFilter的finally代码块中亦可正常关闭;

4 再问:openSession和getCurrentSession的区别

  • 采用getCurrentSession()创建的session在commit或rollback时会自动关闭，
  • 采用openSession()创建的session必须手动关闭
  • 采用getCurrentSession()创建的session会绑定到当前线程中，
  • 采用openSession() 创建的session则不会.所以以上的session是一直都是一个session.

本问题中因为方法A中session (getCurrentSession())在事务中运行, 所以在commit之后被关闭掉了,造成延迟加载事务失败;

5 三问: 为什么开启新事物中的session和当前线程中的session不一致

5.1 spring如何管理hibernate的session

查看配置文件中关于sessionFactory的配置为LocalSessionFactoryBean

LocalSessionFactoryBean` implements FactoryBean<SessionFactory>…….

SessionFactory.getCurrentSession源码追踪
SessionFactoryImpl#getCurrentSession
  1. public Session getCurrentSession() throws HibernateException {
  2.     if ( currentSessionContext == null ) {
  3.         throw new HibernateException( "No CurrentSessionContext configured!" );
  4.     }
  5.     return currentSessionContext.currentSession();
  6. }
SpringSessionContext#currentSession
  1.     public Session currentSession() throws HibernateException {
  2.         /*
  3.         *以sessionFactory为key去当前线程中获取session(此处不再展开源码), 可能是在 OpenSessionInViewFilter 中存入线程的, 参见 OpenSessionInViewFilter 的openSessIon代码
  4.         */
  5.         Object value = TransactionSynchronizationManager.getResource(this.sessionFactory);
  6.         if (value instanceof Session) {
  7.             return (Session) value;
  8.         }
  9.         else if (value instanceof SessionHolder) {
  10.             // hibernate事务管理器
  11.             SessionHolder sessionHolder = (SessionHolder) value;
  12.             Session session = sessionHolder.getSession();
  13.             if (!sessionHolder.isSynchronizedWithTransaction() &&
  14.                     TransactionSynchronizationManager.isSynchronizationActive()) {
  15.                 TransactionSynchronizationManager.registerSynchronization(
  16.                         new SpringSessionSynchronization(sessionHolder, this.sessionFactory, false));
  17.                 sessionHolder.setSynchronizedWithTransaction(true);
  18.                 // Switch to FlushMode.AUTO, as we have to assume a thread-bound Session
  19.                 // with FlushMode.MANUAL, which needs to allow flushing within the transaction.
  20.                 FlushMode flushMode = SessionFactoryUtils.getFlushMode(session);
  21.                 if (flushMode.equals(FlushMode.MANUAL) &&
  22.                         !TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
  23.                     session.setFlushMode(FlushMode.AUTO);
  24.                     sessionHolder.setPreviousFlushMode(flushMode);
  25.                 }
  26.             }
  27.             return session;
  28.         }
  29.         else if (value instanceof EntityManagerHolder) {
  30.             // JpaTransactionManager
  31.             return ((EntityManagerHolder) value).getEntityManager().unwrap(Session.class);
  32.         }
  34.         if (this.transactionManager != null && this.jtaSessionContext != null) {
  35.             try {
  36.                 if (this.transactionManager.getStatus() == Status.STATUS_ACTIVE) {
  37.                     Session session = this.jtaSessionContext.currentSession();
  38.                     if (TransactionSynchronizationManager.isSynchronizationActive()) {
  39.                         TransactionSynchronizationManager.registerSynchronization(
  40.                                 new SpringFlushSynchronization(session));
  41.                     }
  42.                     return session;
  43.                 }
  44.             }
  45.             catch (SystemException ex) {
  46.                 throw new HibernateException("JTA TransactionManager found but status check failed", ex);
  47.             }
  48.         }
  50.         if (TransactionSynchronizationManager.isSynchronizationActive()) {
  51.             Session session = this.sessionFactory.openSession();
  52.             if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
  53.                 session.setFlushMode(FlushMode.MANUAL);
  54.             }
  55.             SessionHolder sessionHolder = new SessionHolder(session);
  56.             TransactionSynchronizationManager.registerSynchronization(
  57.                     new SpringSessionSynchronization(sessionHolder, this.sessionFactory, true));
  58.             TransactionSynchronizationManager.bindResource(this.sessionFactory, sessionHolder);
  59.             sessionHolder.setSynchronizedWithTransaction(true);
  60.             return session;
  61.         }
  62.         else {
  63.             throw new HibernateException("Could not obtain transaction-synchronized Session for current thread");
  64.         }
  65.     }
对比OpenSessionInViewFilter#doFilterInternal ,可以发现两者获取hibernate 的session的逻辑相似;
  1. HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
  2.             throws ServletException, IOException {
  4.         SessionFactory sessionFactory = lookupSessionFactory(request);
  5.         boolean participate = false;
  7.         WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
  8.         String key = getAlreadyFilteredAttributeName();
  10.         if (TransactionSynchronizationManager.hasResource(sessionFactory)) {
  11.             // Do not modify the Session: just set the participate flag.
  12.             participate = true;
  13.         }
  14.         else {
  15.             boolean isFirstRequest = !isAsyncDispatch(request);
  16.             if (isFirstRequest || !applySessionBindingInterceptor(asyncManager, key)) {
  17.                 logger.debug("Opening Hibernate Session in OpenSessionInViewFilter");
  18.                 Session session = openSession(sessionFactory);
  19.                 SessionHolder sessionHolder = new SessionHolder(session);
  20.                 TransactionSynchronizationManager.bindResource(sessionFactory, sessionHolder);
  22.                 AsyncRequestInterceptor interceptor = new AsyncRequestInterceptor(sessionFactory, sessionHolder);
  23.                 asyncManager.registerCallableInterceptor(key, interceptor);
  24.                 asyncManager.registerDeferredResultInterceptor(key, interceptor);
  25.             }
  26.         }
  28.         try {
  29.             filterChain.doFilter(request, response);
  30.         }
  32.         finally {
  33.             if (!participate) {
  34.                 SessionHolder sessionHolder =
  35.                         (SessionHolder) TransactionSynchronizationManager.unbindResource(sessionFactory);
  36.                 if (!isAsyncStarted(request)) {
  37.                     logger.debug("Closing Hibernate Session in OpenSessionInViewFilter");
  38.                     SessionFactoryUtils.closeSession(sessionHolder.getSession());
  39.                 }
  40.             }
  41.         }
spring是如何管理hibernate的事务的?HibernateTransactionManager

本项目配置的hibernate事务管理器为HibernateTransactionManager

HibernateTransactionManager extends AbstractPlatformTransactionManager……

其中获取事务的源码参见:AbstractPlatformTransactionManager#getTransaction
  1.     public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException {
  2.         Object transaction = doGetTransaction();
  4.         // Cache debug flag to avoid repeated checks.
  5.         boolean debugEnabled = logger.isDebugEnabled();
  7.         if (definition == null) {
  8.             // Use defaults if no transaction definition given.
  9.             definition = new DefaultTransactionDefinition();
  10.         }
  12.         if (isExistingTransaction(transaction)) {
  13.             // Existing transaction found -> check propagation behavior to find out how to behave.
  14.             return handleExistingTransaction(definition, transaction, debugEnabled);
  15.         }
  17.         // Check definition settings for new transaction.
  18.         if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
  19.             throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());
  20.         }
  22.         // No existing transaction found -> check propagation behavior to find out how to proceed.
  23.         if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
  24.             throw new IllegalTransactionStateException(
  25.                     "No existing transaction found for transaction marked with propagation 'mandatory'");
  26.         }
  27.         else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
  28.                 definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
  29.                 definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
  30.             SuspendedResourcesHolder suspendedResources = suspend(null);
  31.             if (debugEnabled) {
  32.                 logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
  33.             }
  34.             try {
  35.                 boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
  36.                 DefaultTransactionStatus status = newTransactionStatus(
  37.                         definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
  38.                 doBegin(transaction, definition);
  39.                 prepareSynchronization(status, definition);
  40.                 return status;
  41.             }
  42.             catch (RuntimeException | Error ex) {
  43.                 resume(null, suspendedResources);
  44.                 throw ex;
  45.             }
  46.         }
  47.         else {
  48.             // Create "empty" transaction: no actual transaction, but potentially synchronization.
  49.             if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
  50.                 logger.warn("Custom isolation level specified but no actual transaction initiated; " +
  51.                         "isolation level will effectively be ignored: " + definition);
  52.             }
  53.             boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
  54.             return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
  55.         }
  56.     }
其中dobegin进入HibernateTransactionManager#doBegin
  1.     protected void doBegin(Object transaction, TransactionDefinition definition) {
  2.         HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;
  4.         if (txObject.hasConnectionHolder() && !txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
  5.             throw new IllegalTransactionStateException(
  6.                     "Pre-bound JDBC Connection found! HibernateTransactionManager does not support " +
  7.                     "running within DataSourceTransactionManager if told to manage the DataSource itself. " +
  8.                     "It is recommended to use a single HibernateTransactionManager for all transactions " +
  9.                     "on a single DataSource, no matter whether Hibernate or JDBC access.");
  10.         }
  12.         Session session = null;
  14.         try {
  15.             /*** 判断是否 open一个newSession 见下文说明
  16.             txObject.hasSessionHolder() 一般应返回true,因为在filter中新建了
  17.             txObject.getSessionHolder().isSynchronizedWithTransaction() 何时为true呢?
  18.             在try代码块的末尾会设置其为true: txObject.getSessionHolder().setSynchronizedWithTransaction(true);
  19.             有理由相信 可能是第1+n次进入此dobegin方法时候,如果是txObject中的SessionHolder属性为同一个,则这个属性为true.
  20.             那么什么时候第1+n次进入dobegin,却携带了相同的txObject呢?
  21.             参见:AbstractPlatformTransactionManager#
  22.             DefaultTransactionStatus status = newTransactionStatus(
  23.                         definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
  24.                 doBegin(transaction, definition);
  26.             *************************************/
  27.             if (!txObject.hasSessionHolder() || txObject.getSessionHolder().isSynchronizedWithTransaction()) {
  28.                 Interceptor entityInterceptor = getEntityInterceptor();
  29.                 Session newSession = (entityInterceptor != null ?
  30.                         obtainSessionFactory().withOptions().interceptor(entityInterceptor).openSession() :
  31.                         obtainSessionFactory().openSession());
  32.                 if (logger.isDebugEnabled()) {
  33.                     logger.debug("Opened new Session [" + newSession + "] for Hibernate transaction");
  34.                 }
  35.                 txObject.setSession(newSession);
  36.             }
  38.             session = txObject.getSessionHolder().getSession();
  40.             boolean holdabilityNeeded = this.allowResultAccessAfterCompletion && !txObject.isNewSession();
  41.             boolean isolationLevelNeeded = (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT);
  42.             if (holdabilityNeeded || isolationLevelNeeded || definition.isReadOnly()) {
  43.                 if (this.prepareConnection && isSameConnectionForEntireSession(session)) {
  44.                     // We're allowed to change the transaction settings of the JDBC Connection.
  45.                     if (logger.isDebugEnabled()) {
  46.                         logger.debug("Preparing JDBC Connection of Hibernate Session [" + session + "]");
  47.                     }
  48.                     Connection con = ((SessionImplementor) session).connection();
  49.                     Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
  50.                     txObject.setPreviousIsolationLevel(previousIsolationLevel);
  51.                     if (this.allowResultAccessAfterCompletion && !txObject.isNewSession()) {
  52.                         int currentHoldability = con.getHoldability();
  53.                         if (currentHoldability != ResultSet.HOLD_CURSORS_OVER_COMMIT) {
  54.                             txObject.setPreviousHoldability(currentHoldability);
  55.                             con.setHoldability(ResultSet.HOLD_CURSORS_OVER_COMMIT);
  56.                         }
  57.                     }
  58.                 }
  59.                 else {
  60.                     // Not allowed to change the transaction settings of the JDBC Connection.
  61.                     if (isolationLevelNeeded) {
  62.                         // We should set a specific isolation level but are not allowed to...
  63.                         throw new InvalidIsolationLevelException(
  64.                                 "HibernateTransactionManager is not allowed to support custom isolation levels: " +
  65.                                 "make sure that its 'prepareConnection' flag is on (the default) and that the " +
  66.                                 "Hibernate connection release mode is set to 'on_close' (the default for JDBC).");
  67.                     }
  68.                     if (logger.isDebugEnabled()) {
  69.                         logger.debug("Not preparing JDBC Connection of Hibernate Session [" + session + "]");
  70.                     }
  71.                 }
  72.             }
  74.             if (definition.isReadOnly() && txObject.isNewSession()) {
  75.                 // Just set to MANUAL in case of a new Session for this transaction.
  76.                 session.setFlushMode(FlushMode.MANUAL);
  77.                 // As of 5.1, we're also setting Hibernate's read-only entity mode by default.
  78.                 session.setDefaultReadOnly(true);
  79.             }
  81.             if (!definition.isReadOnly() && !txObject.isNewSession()) {
  82.                 // We need AUTO or COMMIT for a non-read-only transaction.
  83.                 FlushMode flushMode = SessionFactoryUtils.getFlushMode(session);
  84.                 if (FlushMode.MANUAL.equals(flushMode)) {
  85.                     session.setFlushMode(FlushMode.AUTO);
  86.                     txObject.getSessionHolder().setPreviousFlushMode(flushMode);
  87.                 }
  88.             }
  90.             Transaction hibTx;
  92.             // Register transaction timeout.
  93.             int timeout = determineTimeout(definition);
  94.             if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
  95.                 // Use Hibernate's own transaction timeout mechanism on Hibernate 3.1+
  96.                 // Applies to all statements, also to inserts, updates and deletes!
  97.                 hibTx = session.getTransaction();
  98.                 hibTx.setTimeout(timeout);
  99.                 hibTx.begin();
  100.             }
  101.             else {
  102.                 // Open a plain Hibernate transaction without specified timeout.
  103.                 hibTx = session.beginTransaction();
  104.             }
  106.             // Add the Hibernate transaction to the session holder.
  107.             txObject.getSessionHolder().setTransaction(hibTx);
  109.             // Register the Hibernate Session's JDBC Connection for the DataSource, if set.
  110.             if (getDataSource() != null) {
  111.                 SessionImplementor sessionImpl = (SessionImplementor) session;
  112.                 // The following needs to use a lambda expression instead of a method reference
  113.                 // for compatibility with Hibernate ORM <5.2 where connection() is defined on
  114.                 // SessionImplementor itself instead of on SharedSessionContractImplementor...
  115.                 ConnectionHolder conHolder = new ConnectionHolder(() -> sessionImpl.connection());
  116.                 if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
  117.                     conHolder.setTimeoutInSeconds(timeout);
  118.                 }
  119.                 if (logger.isDebugEnabled()) {
  120.                     logger.debug("Exposing Hibernate transaction as JDBC [" + conHolder.getConnectionHandle() + "]");
  121.                 }
  122.                 TransactionSynchronizationManager.bindResource(getDataSource(), conHolder);
  123.                 txObject.setConnectionHolder(conHolder);
  124.             }
  126.             // Bind the session holder to the thread.
  127.             if (txObject.isNewSessionHolder()) {
  128.                 TransactionSynchronizationManager.bindResource(obtainSessionFactory(), txObject.getSessionHolder());
  129.             }
  130.             txObject.getSessionHolder().setSynchronizedWithTransaction(true);
  131.         }
  133.         catch (Throwable ex) {
  134.             if (txObject.isNewSession()) {
  135.                 try {
  136.                     if (session != null && session.getTransaction().getStatus() == TransactionStatus.ACTIVE) {
  137.                         session.getTransaction().rollback();
  138.                     }
  139.                 }
  140.                 catch (Throwable ex2) {
  141.                     logger.debug("Could not rollback Session after failed transaction begin", ex);
  142.                 }
  143.                 finally {
  144.                     SessionFactoryUtils.closeSession(session);
  145.                     txObject.setSessionHolder(null);
  146.                 }
  147.             }
  148.             throw new CannotCreateTransactionException("Could not open Hibernate Session for transaction", ex);
  149.         }
  150.     }

如上 :若 txObject.hasSessionHolder() || txObject.getSessionHolder().isSynchronizedWithTransaction() 返回ture则会新建session

  1. 其中txObject.hasSessionHolder() 一般应返回true,因为多在OpenSessionInViewFilter中新建了

  2. 那txObject.getSessionHolder().isSynchronizedWithTransaction() 何时为true呢?

  • 在try代码块的末尾会设置其为true: txObject.getSessionHolder().setSynchronizedWithTransaction(true);

  • txObject(HibernateTransactionObject)对象来自doGetTransaction()方法

    • txObject的sessionFactory属性来自:(SessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

    • 可知在一个线程中确实是一个对象

HibernateTransactionManager#doGetTransaction
  1.     protected Object doGetTransaction() {
  2.         HibernateTransactionObject txObject = new HibernateTransactionObject();
  3.         txObject.setSavepointAllowed(isNestedTransactionAllowed());
  4.         //获取 sessionFactory, 来自当前HibernateTransactionManager实例的sessionFactory属性
  5.         SessionFactory sessionFactory = obtainSessionFactory();
  6.         //获取当前线程绑定的sessionHolder,来自TransactionSynchronizationManager 的ThreadLocal<Map<Object, Object>> resources
  7.         SessionHolder sessionHolder, =
  8.                 (SessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
  9.         if (sessionHolder != null) {
  10.             if (logger.isDebugEnabled()) {
  11.                 logger.debug("Found thread-bound Session [" + sessionHolder.getSession() + "] for Hibernate transaction");
  12.             }
  13.             txObject.setSessionHolder(sessionHolder);
  14.         }
  15.         else if (this.hibernateManagedSession) {
  16.             try {
  17.                 Session session = sessionFactory.getCurrentSession();
  18.                 if (logger.isDebugEnabled()) {
  19.                     logger.debug("Found Hibernate-managed Session [" + session + "] for Spring-managed transaction");
  20.                 }
  21.                 txObject.setExistingSession(session);
  22.             }
  23.             catch (HibernateException ex) {
  24.                 throw new DataAccessResourceFailureException(
  25.                         "Could not obtain Hibernate-managed Session for Spring-managed transaction", ex);
  26.             }
  27.         }
  29.         if (getDataSource() != null) {
  30.             ConnectionHolder conHolder = (ConnectionHolder)
  31.                     TransactionSynchronizationManager.getResource(getDataSource());
  32.             txObject.setConnectionHolder(conHolder);
  33.         }
  35.         return txObject;
  36.     }

追踪代码而知, 在新建事务的时候,若当前线程之前已经新建了事务,且进入了doBegin方法,则hibernate的事务对象HibernateTransactionObject中持有的SessionHolder对象的synchronizedWithTransaction属性会被设置为true;在这种情况下,新事务下的session为新打开的session,造成和先前的session不一致的情况.

6 留下的疑问:

项目中的serviceA的A方法并没有开启事务(虽然进入事务切面, 但是传播级别是 SUPPORTS)

根据源码只会新建一个空的事务(Create “empty” transaction: no actual transaction, but potentially synchronization.),

而不会进入doBegin,也就不会设置SessionHolder对象的synchronizedWithTransaction属性为true,

那么serviceB的B方法开启新事务的时候, 理应不会打开新的session才对………………….

由于项目在内网环境,无法debug进入源码, 暂时未追踪运行时进入事务源码的代码,且留个疑问, 有暇在外网搭建个环境的时候,再做补充吧.

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