Hibernate源码分析杂记

最近在看hibernate在load entity过程中的操作， 包括为实体类做增强，自动flush，一级缓存，在这里记录一下，慢慢会继续更新。

DefaultLoadEventListener:

final PersistenceContext persistenceContext = event.getSession().getPersistenceContext();

StatefulPersistenceContext.proxiesByKey 缓存实体

DefaultLoadEventListener：

private Object createProxyIfNecessary(
Object proxy = persister.createProxy( event.getEntityId(), event.getSession() );
		persistenceContext.getBatchFetchQueue().addBatchLoadableEntityKey( keyToLoad );
		persistenceContext.addProxy( keyToLoad, proxy );

EventListenerRegistryImpl 注册所有listener， 

private Map<EventType,EventListenerGroupImpl> registeredEventListenersMap = prepareListenerMap();

prepareListenerMap初始化需要的listener，调用prepareListeners完成实际动作。

prepareListeners(
				PRE_COLLECTION_UPDATE,
				workMap
		);

EventType与lisnter接口类对应，保存了event对应的实际处理的lisnter类。 

private EventType(String eventName, Class<? extends T> baseListenerInterface) {
		this.eventName = eventName;
		this.baseListenerInterface = baseListenerInterface;
	}

本身用static方式初始化了eventype对应的listener。

public static final EventType<MergeEventListener> MERGE
			= new EventType<MergeEventListener>( "merge", MergeEventListener.class );

Listener处理实际的event，以DefaultAutoFlushEventListener为例，该listener接收到AutoFlushEvent， 会查找该event内关联的session（用session接口的子接口EventSource），session的实现类是SessionImpl，其声明如下

public final class SessionImpl extends AbstractSessionImpl implements EventSource

DefaultAutoFlushEventListener的方法onAutoFlush(AutoFlushEvent event) 对event的处理如下：

final int oldSize = source.getActionQueue().numberOfCollectionRemovals();
			flushEverythingToExecutions(event);
			if ( flushIsReallyNeeded(event, source) ) {
				LOG.trace( "Need to execute flush" );

				performExecutions(source);
				postFlush(source);
				// note: performExecutions() clears all collectionXxxxtion
				// collections (the collection actions) in the session

				if ( source.getFactory().getStatistics().isStatisticsEnabled() ) {
					source.getFactory().getStatisticsImplementor().flush();
				}
			}

performExecutions中有如下调用，可以看到其根据session中保存的actionQueue进行处理，对action顺序进行重排：

session.getActionQueue().prepareActions();

session.getActionQueue().executeActions();

prepareAction调用保存的action的beforeExecutions方法，对action进行预处理

public void prepareActions() throws HibernateException {
		prepareActions( collectionRemovals );
		prepareActions( collectionUpdates );
		prepareActions( collectionCreations );
		prepareActions( collectionQueuedOps );
	}

executeActions则按顺序执行保存的action，实际调用的是action的execute方法：

	public void executeActions() throws HibernateException {
		if ( ! unresolvedInsertions.isEmpty() ) {
			throw new IllegalStateException(
					"About to execute actions, but there are unresolved entity insert actions."
			);
		}
		executeActions( insertions );
		executeActions( updates );
		// do before actions are handled in the other collection queues
		executeActions( collectionQueuedOps );
		executeActions( collectionRemovals );
		executeActions( collectionUpdates );
		executeActions( collectionCreations );
		executeActions( deletions );
	}

各种CRUD的action都实现了Executable的接口，该接口主要定义了execute()和beforeExecutions()方法，用于执行action前的一些处理操作和之后的实际操作。

action的一些继承层次如下：

public final class EntityInsertAction extends AbstractEntityInsertAction

public abstract class AbstractEntityInsertAction extends EntityAction

public abstract class EntityAction

implements Executable, Serializable, Comparable, AfterTransactionCompletionProcess

performExecutions(EventSource session) 中有这么一句：

session.getTransactionCoordinator().getJdbcCoordinator().flushEnding();

实现类是TransactionCoordinatorImpl， 其构造函数中：

this.jdbcCoordinator = new JdbcCoordinatorImpl( userSuppliedConnection, this );
this.transactionEnvironment = transactionContext.getTransactionEnvironment();

flushEnding中涉及到一个flushDepth，主要处理可能产生多个begin调用，每个begin调用都会让这个depth数量+1， 保证最后的end处理同样数量的flush.

	public void flushEnding() {
		flushDepth--;
		if ( flushDepth < 0 ) {
			throw new HibernateException( "Mismatched flush handling" );
		}
		if ( flushDepth == 0 ) {
			releasesEnabled = true;
		}
		
		afterStatementExecution();
	}

一个查询的处理流程：

Servlet.processRequest->JdbcTransaction.beforeTransactionCommit->SessionImpl.managedFlush->SessinImpl.flush->DefaultFlushEventListener.onFlush

->AbstractFlushingEventListener.performExecutior->JdbcCoordinatorImpl.flushEnding