1.0jpa 2.0

Java EE 7中的非同步持久性上下文

JPA 2.1引入了非同步持久性上下文的概念，該概念允許對JPA實體管理器的刷新進行細粒度控制，即通過顯式調用EntityManager＃joinTransaction 。 以前，這默認情況下是JTA事務的結束，例如在典型的Stateless EJB中，實體管理器會在方法結束時（默認情況下開始和結束事務）將其狀態刷新到DB。 您可以在此處和此處閱讀有關此內容的更多信息。

在Java EE 7之前的時代（EE 5和EE 6）也有可能

可以對Java EE 5和6進行調整，以實現與Java EE 7中非同步持久性上下文所獲得的結果相同的結果。

想象一下一個用例，其中按順序（使用流程之類的向導）編輯客戶詳細信息，例如屏幕1中的地址信息，屏幕2中的聯系信息等。您希望在客戶輸入是但不希望將整個狀態推送到數據庫，直到該過程完成，即用戶輸入了所有類別的信息

package com.abhirockzz.conversationalee;import com.abhirockzz.conversationalee.entity.Customer; import java.util.Date; import javax.annotation.PostConstruct; import javax.annotation.PreDestroy; import javax.ejb.Remove; import javax.ejb.Stateful; import javax.ejb.TransactionAttribute; import javax.ejb.TransactionAttributeType; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.PersistenceContextType;@Stateful @TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED) public class CustomerEditorFacade{@PersistenceContext(type = PersistenceContextType.EXTENDED)EntityManager em;@Inject //this won't work in Java EE 5Principal authenticatedUser;private Customer customer;@PostConstructpublic void init(){System.out.println("CustomerEditorFacade created at " + new Date().toString()); }@PreDestroypublic void destroy(){System.out.println("CustomerEditorFacade destroyed at " + new Date().toString()); }//step 1public void updateCity(String custID, String city){String custID = authenticatedUser.getName(); //assume we have an authenticated principal which is the same as the customer ID in the DatabaseCustomer customerFromDB = em.find(Customer.class, Integer.valueOf(custID)); //obtain a 'managed' entitycustomerFromDB.setCity(city); //no need to call em.persistcustomer = customerFromDB; //just switch references//Customer state will NOT be pushed to DB}//step 2public void updateEmail(String email){customer.setEmail(email); //not pushed to DB yet}@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)public void save(){//dummy method to trigger transaction and flush EM state to DB}@Removepublic void finish(){//optional method to provide a way to evict this bean once used//not required if this is session scoped}}

代碼注釋是自我解釋（希望如此）

干杯!

翻譯自: https://www.javacodegeeks.com/2015/12/pre-java-ee-7-alternative-jpa-2-1-unsynchronized-persistence-context.html

1.0jpa 2.0

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