[原]Jackrabbit使用介绍

编程

spring modules jcr

spring-modules-jcr 是jackrabbit与spring集成的第三方模块，可以简化JSR-170 API使用。连接：http://www.infoq.com/cn/articles/spring-modules-jcr

spring-modules-jcr主要是通过JcrTemplate中的execute方法操作jackrabbit的读写。在没有事务的环境下，每一个execute都使用独立的session，方法执行完后立即释放。

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/**
	 * @see org.springmodules.jcr.JcrOperations#execute(org.springmodules.jcr.JcrCallback,
	 *      boolean)
	 */
	public Object execute(JcrCallback action, boolean exposeNativeSession) throws DataAccessException {
 		Session session = getSession();
                //判断当前是否在事务下
		boolean existingTransaction = SessionFactoryUtils.isSessionThreadBound(session, getSessionFactory());
		if (existingTransaction) {
			logger.debug("Found thread-bound Session for JcrTemplate");
		}

		try {
			Session sessionToExpose = (exposeNativeSession ? session : createSessionProxy(session));
			Object result = action.doInJcr(sessionToExpose);
			// TODO: does flushing (session.refresh) should work here?
			// flushIfNecessary(session, existingTransaction);
			return result;
		}
		catch (RepositoryException ex) {
			throw convertJcrAccessException(ex);
			// IOException are not converted here
		}
		catch (IOException ex) {
			// use method to decouple the static call
			throw convertJcrAccessException(ex);
		}
		catch (RuntimeException ex) {
			// Callback code threw application exception...
			throw convertJcrAccessException(ex);
		}
		finally {
			if (existingTransaction) {
				logger.debug("Not closing pre-bound Jcr Session after JcrTemplate");
			}
			else {
                     //不在事务环境下，立即释放session
				SessionFactoryUtils.releaseSession(session, getSessionFactory());

			}
		}
	}
~

测试代码

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public void executeTask()
	{
		logger.debug("get the Gadget class Bean,DagetDao={}", dao);
                //添加节点
		dao.addNodeIfAbsent("Gadget");
                //查询节点
		boolean result = dao.nodeExists("Gadget");
		logger.debug("add Node success or not ,{}",result);
		try{
                //删除节点
			dao.deleteNodebyName("Gadget");

		}
		catch (Exception e)
		{
			e.printStackTrace();
		}
                //再次查询节点
		logger.debug("Node exist or not ,{}",dao.nodeExists("Gadget"));
	}

上面测试代码总共4次操作jackrabbit，应该使用4个session

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2015-08-20 20:24:42 [main] DEBUG org.springmodules.jcr.JcrSessionFactory -no session holder provider manager set; using the default one
2015-08-20 20:24:42 [thread-0] DEBUG com.huawei.jackrabbit.test.service.GadgetnoTransactionService -get the Gadget class Bean,DagetDao=com.huawei.jackrabbit.test.DAO.GadgetDao@1e22c75
2015-08-20 20:24:42 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Opening JCR Session
2015-08-20 20:24:42 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -Starting from root node.  node=node /
2015-08-20 20:24:43 [thread-0] INFO  com.huawei.jackrabbit.test.DAO.GadgetDao -Saved node.  node=node /Gadget
2015-08-20 20:24:43 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Closing JCR Session
2015-08-20 20:24:43 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Opening JCR Session
2015-08-20 20:24:43 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -Starting from root node.  node=node /
2015-08-20 20:24:43 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Closing JCR Session
2015-08-20 20:24:43 [thread-0] DEBUG com.huawei.jackrabbit.test.service.GadgetnoTransactionService -add Node success or not ,true
2015-08-20 20:24:43 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Opening JCR Session
2015-08-20 20:24:43 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -delete the node name =Gadget
2015-08-20 20:24:43 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -the node exist or not ,false
2015-08-20 20:24:43 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Closing JCR Session
2015-08-20 20:24:43 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Opening JCR Session
2015-08-20 20:24:43 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -Starting from root node.  node=node /
2015-08-20 20:24:43 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Closing JCR Session
2015-08-20 20:24:43 [thread-0] DEBUG com.huawei.jackrabbit.test.service.GadgetnoTransactionService -Node exist or not ,false

打印日志可以看出4次打开和关闭session

在事务环境下，每个事务都独立使用一个session，事务提交之后立即释放。所以上面的测试代码在事务下只使用一个session

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2015-08-21 09:16:06 [main] DEBUG org.springmodules.jcr.JcrSessionFactory -no session holder provider manager set; using the default one
2015-08-21 09:16:06 [thread-0] DEBUG org.springmodules.jcr.jackrabbit.LocalTransactionManager -Creating new transaction with name [com.huawei.jackrabbit.test.service.GadgetService.executeTask]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT; ''
2015-08-21 09:16:06 [thread-0] DEBUG org.springmodules.jcr.jackrabbit.LocalTransactionManager -Opened new session [session-admin-3] for JCR transaction
2015-08-21 09:16:06 [thread-0] DEBUG com.huawei.jackrabbit.test.service.GadgetService -get the Gadget class Bean,DagetDao=com.huawei.jackrabbit.test.DAO.GadgetDao@115470e
2015-08-21 09:16:06 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Found thread-bound Session for JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -Starting from root node.  node=node /
2015-08-21 09:16:07 [thread-0] INFO  com.huawei.jackrabbit.test.DAO.GadgetDao -Saved node.  node=node /Gadget
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Not closing pre-bound Jcr Session after JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Found thread-bound Session for JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -Starting from root node.  node=node /
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Not closing pre-bound Jcr Session after JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG com.huawei.jackrabbit.test.service.GadgetService -add Node success or not ,true
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Found thread-bound Session for JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -delete the node name =Gadget
2015-08-21 09:16:07 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -the node exist or not ,false
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Not closing pre-bound Jcr Session after JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Found thread-bound Session for JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG com.huawei.jackrabbit.test.DAO.GadgetDao -Starting from root node.  node=node /
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.JcrTemplate -Not closing pre-bound Jcr Session after JcrTemplate
2015-08-21 09:16:07 [thread-0] DEBUG com.huawei.jackrabbit.test.service.GadgetService -Node exist or not ,false
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.jackrabbit.LocalTransactionManager -Initiating transaction commit
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.jackrabbit.LocalTransactionManager -Committing JCR transaction on session [session-admin-3]
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.jackrabbit.LocalTransactionManager -Closing JCR session [session-admin-3] after transaction
2015-08-21 09:16:07 [thread-0] DEBUG org.springmodules.jcr.SessionFactoryUtils -Closing JCR Session

上面的日志显示本次操作只使用了[session-admin-3] session

嵌套事务使用
spring中默认配置事务传播机制为PROPAGATION_REQUIRED

如果当前处在事务中调用另一事务方法，会被合成一个事务。图中事务方法2发生异常，进行事务回滚后，事务方法1结束后会提交事务，事务已经回滚再次提交会报异常

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encountered an error.org.springframework.transaction.UnexpectedRollbackException: Transaction rolled back because it has been marked as rollback-only
    at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:252)
    at java.util.concurrent.FutureTask.get(FutureTask.java:111)

在实际使用中需要注意嵌套事务的使用。

事务和非事务性能对比

根据节点名来查询jackrabbit节点是否存在，比较在事务和非事务下的性能差异

在事务和非事务下使用50线程分别查询节点并统计查询消耗的平均时间、最大和最大时间
非事务下又分为使用单一session和多session场景，下面是数据统计：

  1. 使用事务，50个线程有50个事务

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    -average time:88(ms), max time :94(ms), min time :86(ms)

  2. 非事务，每次查询都使用新session

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    -average time:44(ms), max time :54(ms), min time :39(ms)

  3. 非事务，每次查询使用同一session

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    -average time:12(ms), max time :23(ms), min time :8(ms)

对比使用单一session耗时最小，性能最佳，使用事务性能最差，但是从事务的ACID特性考虑，使用单一session和多个session不满足原子性要求
上面测试代码executeTask方法在多线程下使用单一session操作会报 javax.jcr.InvalidItemStateException异常，使用多session操作 报javax.jcr.ItemNotFoundException异常。而在事务环境下可以正常完成。
是否使用事务需要从业务的使用场景考虑，如果业务场景就满足原子性操作，或者异常有处理措施保证数据一致性，那么不使用事务也可以，但是这种往往比较复杂对session使用也需要谨慎考虑。
考虑一种场景，一次性添加多个节点，要不全部成功要不全部失败，如果中途失败，前面添加的节点都需要删除，在事务下可以回滚状态，在非事务下就必须代码删除，这样处理很复杂而且容易出错