hibernate 使用的设计模式（一） 观察者（50校招生网）

hibernate 使用的设计模式（一） 观察者（50校招生网）

  以hibernate.get(String, Serializable)方法为例：

  get()的方法实现为：

   图1：

public Object get(String entityName, Serializable id, LockMode lockMode) throws HibernateException {LoadEvent event = new LoadEvent(id, entityName, lockMode, this);   fireLoad(event, LoadEventListener.GET);return event.getResult();}private void fireLoad(LoadEvent event, LoadType loadType) {errorIfClosed();checkTransactionSynchStatus();LoadEventListener[] loadEventListener = listeners.getLoadEventListeners();for ( int i = 0; i < loadEventListener.length; i++ ) {loadEventListener[i].onLoad(event, loadType);}}

   图2：

public void onLoad(LoadEvent event, LoadEventListener.LoadType loadType) throws HibernateException {final SessionImplementor source = event.getSession();EntityPersister persister;if ( event.getInstanceToLoad() != null ) {persister = source.getEntityPersister( null, event.getInstanceToLoad() ); //the load() which takes an entity does not pass an entityNameevent.setEntityClassName( event.getInstanceToLoad().getClass().getName() );}else {persister = source.getFactory().getEntityPersister( event.getEntityClassName() );}if ( persister == null ) {throw new HibernateException("Unable to locate persister: " +event.getEntityClassName());}if ( persister.getIdentifierType().isComponentType() && EntityMode.DOM4J == event.getSession().getEntityMode() ) {// skip this check for composite-ids relating to dom4j entity-mode;// alternatively, we could add a check to make sure the incoming id value is// an instance of Element...}else {Class idClass = persister.getIdentifierType().getReturnedClass();if ( idClass != null && ! idClass.isInstance( event.getEntityId() ) ) {throw new TypeMismatchException("Provided id of the wrong type for class " + persister.getEntityName() + ". Expected: " + idClass + ", got " + event.getEntityId().getClass());}}EntityKey keyToLoad = new EntityKey( event.getEntityId(), persister, source.getEntityMode()  );try {if ( loadType.isNakedEntityReturned() ) {//do not return a proxy!//(this option indicates we are initializing a proxy)event.setResult( load(event, persister, keyToLoad, loadType) );}else {//return a proxy if appropriateif ( event.getLockMode() == LockMode.NONE ) {event.setResult( proxyOrLoad(event, persister, keyToLoad, loadType) );}else {event.setResult( lockAndLoad(event, persister, keyToLoad, loadType, source) );}}}catch(HibernateException e) {log.info("Error performing load command", e);throw e;}}

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   如代码所示：当执行get()方法时，首先创建一个loadEvent，然后触发加载操作，获取对应listeners做出对应的响应；

   SessionImpl为被观察者， listers为观察者， event为事件， event中包含了事件相关的属性。

ps:图1中为SessionImpl中的代码（SessionImpl为session的实现类）， 图2为DefaultLoadEventListener的代码（DefaultLoadEventListener为LoadEventListener的实现类）