在线一区二区三区视频,国产成人97精品免费看片,亚洲片在线资源

gembin

OSGi, Eclipse Equinox, ECF, Virgo, Gemini, Apache Felix, Karaf, Aires, Camel, Eclipse RCP

HBase, Hadoop, ZooKeeper, Cassandra

Flex4, AS3, Swiz framework, GraniteDS, BlazeDS etc.

There is nothing that software can't fix. Unfortunately, there is also nothing that software can't completely fuck up. That gap is called talent.

About Me

Thread-safety when injecting JPA EntityManager

Injecting EJB 3 stateful beans into servlet instance fields is not thread-safe. Along the same line, injecting EntityManager with @PersistenceContext into servlet instance variables is not thread-safe, either. EntityManager is just not designed to be thread-safe.

For example, the following code snippet of a servlet class is incorrect:

?

1

2

3

4

5

6

7

public class EMTestServlet extends HttpServlet {

  //This field injection is not thread-safe.

  //FIXME

  @PersistenceContext

  private EntityManager em;

...

}

One way to fix this is to inject EntityManagerFactory instead. EntityManagerFactory is guaranteed to be thread-safe. For example:

?

public class EMTestServlet extends HttpServlet {

  //This field injection is thread-safe

  @PersistenceUnit

  private EntityManagerFactory emf;

  protected void doGet(HttpServletRequest request,

             HttpServletResponse response)

  throws ServletException, IOException {

  EntityManager em = emf.createEntityManager();

  //work with em

}

}

Continuing container-managed EntityManager vs application-managed EntityManager.

There are important differences between the injected EntityManager, and the EntityManager created from an injected EntityManagerFactory. Basically, injected EntityManager is container-managed, meaning all of its lifecycle is controlled by the container (web container or EJB container). Application code cannot close it, or otherwise interfere with its life.

In addition, for a container-managed EntityManager, its associated PersistenceContext is automatically propagated along with the underlying JTA, from servlet A to servlet B, from servlet to EJB, from EJB a to EJB B, and so on. As such, EntityManager of the same configuration injected into various classes can share the same PersistenceContext in a call stack.

On the other hand, EntityManager created from EntityManagerFactory is application-managed EntityManager. Application code is responsible for managing its whole lifecycle. And there is no PersistenceContext propagation for application-managed EntityManager.

Are all EntityManager's obtained from EntityManagerFactory application-managed EntityManager? Yes.

Is it possible to get a container-managed EntityManager from EntityManagerFactory? No.

You may have read about the method EntityManagerFactory.getEntityManager(), which returns a container-managed EntityManager. This method was considered and included in the early draft version of Java Persistence API, but was eventually removed from its final release.

posted on 2013-02-04 10:49 gembin 閱讀(819) 評論(0) 編輯收藏所屬分類: JavaEE

新用戶注冊刷新評論列表


只有注冊用戶登錄后才能發表評論。




網站導航: 博客園 IT新聞 Chat2DB C++博客博問管理
相關文章: Thread-safety when injecting JPA EntityManager WebLogic's Classloading Framework Common Problems with Authentication Provider Configuration Enterprise Java Community: Modularizing Existing Web Applications With OSGi: A Migration Path to OSGi [zhuan] Higgins 1.0: Identity Management Solutions from the Eclipse Foundation JSP使用URLRewirte實現url地址偽靜態化(轉) filter過濾器 Apache Common fileUpload API 詳解 Core J2EE Pattern Job Scheduling in J2EE Applications

gembin

Thread-safety when injecting JPA EntityManager

導航

統計

常用鏈接

留言簿(6)

隨筆分類(440)

隨筆檔案(378)

文章檔案(6)

新聞檔案(1)

相冊

收藏夾(9)

Adobe

Android

AS3

Blog-Links

Build

Design Pattern

Eclipse

Favorite Links

Flickr

Game Dev

HBase

Identity Management

IT resources

JEE

Language

OpenID

OSGi

SOA

Version Control

最新隨筆

搜索

積分與排名

最新評論

閱讀排行榜

評論排行榜