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    <p>EJB are transactional components. The transaction can be managed either by the applicaiton server itself (CMT - container-managed transaction), or manually by yourself within the EJB (BMT - bean-managed transaction).</p> <p>EJB supports distributed transaction through the JTA specification. The distributed transaction is controlled using <a href="http://java.sun.com/products/jta/javadocs-1.0.1/javax/transaction/UserTransaction.html" rel="noreferrer"><code>UserTransaction</code></a>, which has methods <code>begin</code>, <code>commit</code>, <code>rollback</code>.</p> <p>With CMT, the application server starts, commit and rollback the transaction (according to the <a href="http://java.sun.com/products/ejb/javadoc-3_0-fr/javax/ejb/TransactionAttributeType.html" rel="noreferrer">transaction annotations</a>) for you and you are not allowed to interfere. This means you must not access the <code>UserTransaction</code> in this case. However, with BMT, you do that manually and you control the transaction yourself using the <code>UserTransaction</code>.</p> <p>Let's move now to the <code>EntityManager</code>. A JPA implementation can be used either within an application server or stand-alone. If use in stand-alone, you need to use <code>EntityManage.getTransaction</code> to demarcate the JDBC transaction yourself. If used within an application server, the <code>EntityManager</code> cooperated with the JTA distributed transaction manager transparently for you. </p> <p>Most of the time, you use CMT with <code>@Required</code> annotation on the EJB. This means that you don't need to access neither <code>UserTransaction</code> nor <code>EntityManager.getTransaction</code>. The app. server starts and commits the transaction, but also takes care to rollback if an exception is raised. This is what I would recommend for your facade.</p> <p>(There are more subtleties, such as the <a href="http://java.sun.com/javaee/5/docs/api/javax/persistence/PersistenceContextType.html#TRANSACTION" rel="noreferrer"><code>PersistenceContextType</code></a> or the manual enlistment of the entity manager in distributed transaction with <a href="http://java.sun.com/javaee/5/docs/api/javax/persistence/EntityManager.html#joinTransaction%28%29" rel="noreferrer"><code>EntityManager.joinTransaction</code></a>, but that's only if you use the technologies in a different ways as the default).</p>
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    1. POWhat is difference between @Resource UserTransaction and EntityManager.getTransaction()
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    1. POWhat is difference between @Resource UserTransaction and EntityManager.getTransaction()
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    1. COAre you sure that `EntityManager#getTransaction()` cooperates with the JTA distributed transaction when running inside an app server? I don't think it does, my understanding is that it returns a resource-local transaction that can be used to persist data *outside* of the current JTA transaction.
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    2. CO@Pascal The `EntityManager` cooperates with JTA so you shouldn't use `EntityManager#getTransaction` at all. As per the javadoc, `EntityManager#getTransaction` throws `IllegalStateException` if invoked on a JTA EntityManager.
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    3. COIndeed, `getTransaction` throws an exception when invoked on a JTA EntityManager). Actually, the example I had in mind (from "Pro JPA 2") is to get an application managed, resource-local EM in a Session Bean - e.g. for audit logging - and a resource local transaction that you can begin/commit as many time as you want outside the JTA transaction. But I realize that I misread your answer, this is different from what you wrote. Thanks!
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