Java Hibernate事务和JTA

所以我在回顾我几年前参与的一个遗留项目。我注意到一些困扰了我几天的事情。此应用程序使用两个不同的筛选器进行事务处理。一个过滤器名为HibernateFilter，另一个过滤器名为TransactionFilter（请参阅下面的代码）

我的问题是：为什么要使用第二个TransactionFilter？HibernateFilter还不够吗

我希望这里有人能解释这一点，或者如果我遗漏了什么

休眠过滤器：

     public void doFilter(ServletRequest request,
                       ServletResponse response,
                       FilterChain chain)
      throws IOException, ServletException {
    if (request.getAttribute(FILTER_APPLIED) == null) {
      request.setAttribute(FILTER_APPLIED, FILTER_APPLIED);
      applyFilter(request, response, chain);
    } else {
      chain.doFilter(request, response);
    }
  }

  private void applyFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException {
    try {
      if (sf == null) {
        log.info("SessionFactory assigned from XMLConfig!");
        sf = XMLConfig.getSessionFactory();
      }
      log.debug("Starting a database transaction");
      sf.getCurrentSession().beginTransaction();

      // Call the next filter (continue request processing)
      chain.doFilter(request, response);

      // Commit and cleanup
      log.debug("Committing the database transaction");
      sf.getCurrentSession().getTransaction().commit();

    } catch (Throwable ex) {
      log.error("HibernateFilter, intressting error: " + getRequestUrl(request) + " " + ex, ex);
      // Rollback only
      try {
        log.debug("Trying to rollback database transaction after exception");
        sf.getCurrentSession().getTransaction().rollback();
      } catch (Throwable rbEx) {
        log.error("Could not rollback transaction after exception!", rbEx);
      }

      // Let others handle it... maybe another interceptor for exceptions?
      throw new ServletException(ex);
    }
  }

     public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

    // Boot the session!!!
    HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
    HttpSession session = httpServletRequest.getSession(true);
    session.setAttribute(this.getClass().getName(),"Session forced to start!");

    // Start orion transaction...
    Object attribute = servletRequest.getAttribute(FILTER_APPLIED);
    if (attribute == null) {
      servletRequest.setAttribute(FILTER_APPLIED, FILTER_APPLIED);
      applyFilter(servletRequest, servletResponse, filterChain);
    } else {// Skip filter if run more than once for a request.
      filterChain.doFilter(servletRequest, servletResponse);
    }

  }

  private void applyFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws ServletException {
    TransactionManager manager = null;
    try {
      manager = (TransactionManager) new InitialContext().lookup("java:comp/UserTransaction");
      if (manager != null) {
        manager.begin();
      }
    } catch (NamingException e) {
      LOG.error("Cant find TransactionManager!", e);
    } catch (SystemException e) {
      LOG.error("Error starting transaction!", e);
    } catch (NotSupportedException e) {
      LOG.error("begin() not supported!", e);
    }
    try {
      filterChain.doFilter(servletRequest, servletResponse);
      if (manager != null) {
        manager.commit();
      }
    } catch (Exception e) {
      try {
        if (manager != null) {
          manager.rollback();
          // Let others handle the rest... maybe another interceptor for exceptions?
          throw new ServletException(e);
        }
      } catch (SystemException e1) {
        LOG.error("Couldn't rollback!", e1);
      }
    }

TransactionFilter:

     public void doFilter(ServletRequest request,
                       ServletResponse response,
                       FilterChain chain)
      throws IOException, ServletException {
    if (request.getAttribute(FILTER_APPLIED) == null) {
      request.setAttribute(FILTER_APPLIED, FILTER_APPLIED);
      applyFilter(request, response, chain);
    } else {
      chain.doFilter(request, response);
    }
  }

  private void applyFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException {
    try {
      if (sf == null) {
        log.info("SessionFactory assigned from XMLConfig!");
        sf = XMLConfig.getSessionFactory();
      }
      log.debug("Starting a database transaction");
      sf.getCurrentSession().beginTransaction();

      // Call the next filter (continue request processing)
      chain.doFilter(request, response);

      // Commit and cleanup
      log.debug("Committing the database transaction");
      sf.getCurrentSession().getTransaction().commit();

    } catch (Throwable ex) {
      log.error("HibernateFilter, intressting error: " + getRequestUrl(request) + " " + ex, ex);
      // Rollback only
      try {
        log.debug("Trying to rollback database transaction after exception");
        sf.getCurrentSession().getTransaction().rollback();
      } catch (Throwable rbEx) {
        log.error("Could not rollback transaction after exception!", rbEx);
      }

      // Let others handle it... maybe another interceptor for exceptions?
      throw new ServletException(ex);
    }
  }

     public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

    // Boot the session!!!
    HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
    HttpSession session = httpServletRequest.getSession(true);
    session.setAttribute(this.getClass().getName(),"Session forced to start!");

    // Start orion transaction...
    Object attribute = servletRequest.getAttribute(FILTER_APPLIED);
    if (attribute == null) {
      servletRequest.setAttribute(FILTER_APPLIED, FILTER_APPLIED);
      applyFilter(servletRequest, servletResponse, filterChain);
    } else {// Skip filter if run more than once for a request.
      filterChain.doFilter(servletRequest, servletResponse);
    }

  }

  private void applyFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws ServletException {
    TransactionManager manager = null;
    try {
      manager = (TransactionManager) new InitialContext().lookup("java:comp/UserTransaction");
      if (manager != null) {
        manager.begin();
      }
    } catch (NamingException e) {
      LOG.error("Cant find TransactionManager!", e);
    } catch (SystemException e) {
      LOG.error("Error starting transaction!", e);
    } catch (NotSupportedException e) {
      LOG.error("begin() not supported!", e);
    }
    try {
      filterChain.doFilter(servletRequest, servletResponse);
      if (manager != null) {
        manager.commit();
      }
    } catch (Exception e) {
      try {
        if (manager != null) {
          manager.rollback();
          // Let others handle the rest... maybe another interceptor for exceptions?
          throw new ServletException(e);
        }
      } catch (SystemException e1) {
        LOG.error("Couldn't rollback!", e1);
      }
    }

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为什么要这样做，有不同的选择，大多数都是当时没有人知道的

但至少我可以给你一个场景，在这个场景中，这部分是有意义的。但在此之前，我要介绍一些hibernate/JPA/JTA的基本原理

Hibernate尤其是SessionFactory是一个只支持Hibernate的机制，而不是java标准的一部分。这就是您的团队用于hibernate相关交互的内容

JPA是关于对象关系映射的java标准，它的大部分灵感来自hibernate。与JPA结合使用更常见的是EntityManager和EntityManager工厂。这可以与hibernate结合使用，因为hibernate是标准的实现。在大多数情况下，您可以启动事务提交，。。。使用Hibernate会话和EntityManager

JTA是Java事务API。这只是在应用程序中处理事务的标准。@Transactional注释是本规范的一部分，通常与JPA实现结合使用。这两个标准旨在很好地协同工作。不可能同时使用EntityManager和JTA规范中的事务管理（如果我没记错的话）。但是除了与JPA结合使用之外，该规范根本不限于JPA或数据库。此标准还可用于确保JMS资源的事务处理。基本上，任何正确实现标准的东西都可以被“事务性”处理。只要将某个东西视为数据源，不管它是什么

让我们来看看为什么使用它。我假设有一个应用服务器正在使用，其中配置了数据源并处理事务。例如JMS资源。另一方面，他们希望使用hibernate作为持久性提供者。现在有了不同的选项，为什么他们没有使用基于JPA的数据源和hibernate作为持久性提供者。一个是应用服务器有一个捆绑的JPA实现，团队无法否决/替换它。另一个原因是他们想使用hibernate自定义特性，这些特性不是JPA规范的一部分，他们无法将其与JPA方式结合起来

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总而言之，有很多选择，我的答案是很多猜测，但我希望它至少有一点帮助

正如我正确理解的那样，第一个处理数据库事务，而不考虑通过低级HibernateAPI关闭任何用户会话。第二种方法强制每个请求都有一个用户会话，该请求在开始和结束时启动和提交。关于环境，这是运行第二个应该会导致与第一个相同的行为。