Java UserTransaction 和 EntityTransaction 的区别
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Difference between UserTransaction and EntityTransaction
提问by bguiz
Title says it all: What is the difference between a UserTransactionand an EntityTransaction?
标题说明了一切： aUserTransaction和 an之间有什么区别EntityTransaction？
My rudimentary understanding is that UserTransactionis used when JTA is required (e.g. to do queries on mulitple things), and that EntityTransactionis used when JPA only is required (e.g. when the query is atomic).
我的基本理解是UserTransaction在需要 JTA 时使用（例如对多个事物进行查询），而EntityTransaction在仅需要 JPA 时使用（例如当查询是原子时）。
Is that the only difference between the two or is there more to it than that?
这是两者之间的唯一区别还是除此之外还有更多区别？
采纳答案by ewernli
My rudimentary understanding is that UserTransaction is used when JTA is required (e.g. to do queries on mulitple things), and that EntityTransaction is used when JPA only is required (e.g. when the query is atomic).
我的基本理解是 UserTransaction 在需要 JTA 时使用（例如对多个事物进行查询），而 EntityTransaction 在仅需要 JPA 时使用（例如当查询是原子的时）。
That's basically right, but your description of "multiple things" and "atomic" is a bit strange. JTA allows the developper to use distributed transaction to perform changes on multiples resources (database, JMS broker, etc.) atomically (all-or-nothing). If only one resource is accessed (e.g. one single database), you don't need JTA, but the transaction is still atomic (all-or-nothing). That's for instance the case when you use a regular JDBC transaction on one database.
基本上是对的，但是你对“多事物”和“原子”的描述有点奇怪。JTA 允许开发人员使用分布式事务以原子方式（全有或全无）对多个资源（数据库、JMS 代理等）执行更改。如果只访问一个资源（例如一个数据库），则不需要 JTA，但事务仍然是原子的（全有或全无）。例如，当您在一个数据库上使用常规 JDBC 事务时就是这种情况。
Considering UserTransactionvs. EntityTransaction:
考虑UserTransactionvs. EntityTransaction：
- If JPA is use stand-alone, you use
EntityTransactionto demarcate the transaction yourself. - If JPA is used within a managed environment where it integrates with JTA, you use
UserTransaction. TheEntityManagerhooks itself into the JTA distributed transaction manager. The only subtlety I'm aware of considers the flush of the changes. WhenEntityTransactionis used, JPA know it needs to flush the changes. If transaction are controlled usingUserTransaction, it needs to register a callback using JTAregisterSynchronization, so that the changes are flushed to the database before the transaction completes. If you use EJB with CMT (container managed transaction), you don't even need to useUserTransaction: the app server starts and stops the transactions for you.
- 如果 JPA 是独立使用的，则使用您
EntityTransaction自己来划分事务。 - 如果在与 JTA 集成的托管环境中使用 JPA，则使用
UserTransaction. 将EntityManager自身挂接到 JTA 分布式事务管理器中。我所知道的唯一微妙之处是考虑了变化的冲洗。何时EntityTransaction使用，JPA 知道它需要刷新更改。如果使用 控制事务UserTransaction，则需要使用 JTA 注册回调registerSynchronization，以便在事务完成之前将更改刷新到数据库。如果您将 EJB 与 CMT（容器管理事务）一起使用，您甚至不需要使用UserTransaction：应用服务器为您启动和停止事务。
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