如何自定义Hibernate脏检查机制

介绍

在上一篇文章中，我描述了Hibernate自动脏检查机制。尽管您应该始终喜欢它，但是有时您可能想添加自己的自定义污垢检测策略。

自定义脏检查策略

Hibernate提供以下定制机制：

休眠拦截器#findDirty（）
CustomEntityDirtinessStrategy

手动检查脏物

作为练习，我将构建一个手动的脏检查机制，以说明自定义更改检测策略的难易程度：

自脏检查实体

首先，我将定义一个DirtyAware接口，所有手动脏检查实体都必须实现：

public interface DirtyAware {Set<String> getDirtyProperties();void clearDirtyProperties();
}

接下来，我将在基类中封装当前的脏检查逻辑：

public abstract class SelfDirtyCheckingEntity implements DirtyAware {private final Map<String, String> setterToPropertyMap = new HashMap<String, String>();@Transientprivate Set<String> dirtyProperties = new LinkedHashSet<String>();public SelfDirtyCheckingEntity() {try {BeanInfo beanInfo = Introspector.getBeanInfo(getClass());PropertyDescriptor[] descriptors = beanInfo.getPropertyDescriptors();for (PropertyDescriptor descriptor : descriptors) {Method setter = descriptor.getWriteMethod();if (setter != null) {setterToPropertyMap.put(setter.getName(), descriptor.getName());}}} catch (IntrospectionException e) {throw new IllegalStateException(e);}}@Overridepublic Set<String> getDirtyProperties() {return dirtyProperties;}@Overridepublic void clearDirtyProperties() {dirtyProperties.clear();}protected void markDirtyProperty() {String methodName = Thread.currentThread().getStackTrace()[2].getMethodName();dirtyProperties.add(setterToPropertyMap.get(methodName));}
}

所有手动的脏检查实体都必须扩展此基类，并通过调用markDirtyProperty方法显式标记脏属性。

实际的自脏检查实体如下所示：

@Entity
@Table(name = "ORDER_LINE")
public class OrderLine extends SelfDirtyCheckingEntity {@Id@GeneratedValue(strategy = GenerationType.AUTO)private Long id;private Long number;private String orderedBy;private Date orderedOn;public Long getId() {return id;}public Long getNumber() {return number;}public void setNumber(Long number) {this.number = number;markDirtyProperty();}public String getOrderedBy() {return orderedBy;}public void setOrderedBy(String orderedBy) {this.orderedBy = orderedBy;markDirtyProperty();}public Date getOrderedOn() {return orderedOn;}public void setOrderedOn(Date orderedOn) {this.orderedOn = orderedOn;markDirtyProperty();}
}

每当调用setter时，关联的属性就会变脏。为简单起见，当我们将属性还原为其原始值时，此简单练习不涵盖用例。

脏检查测试

为了测试自脏检查机制，我将运行以下测试用例：

@Test
public void testDirtyChecking() {doInTransaction(new TransactionCallable<Void>() {@Overridepublic Void execute(Session session) {OrderLine orderLine = new OrderLine();session.persist(orderLine);session.flush();orderLine.setNumber(123L);orderLine.setOrderedBy("Vlad");orderLine.setOrderedOn(new Date());session.flush();orderLine.setOrderedBy("Alex");return null;}});
}

Hibernate拦截器解决方案

Hibernate Interceptor findDirty回调使我们能够控制脏属性发现过程。该方法可能返回：

null ，将脏检查委托给Hibernate默认策略
一个int []数组，其中包含修改后的属性索引

我们的Hibernate脏检查拦截器如下所示：

public class DirtyCheckingInterceptor extends EmptyInterceptor {@Overridepublic int[] findDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types) {if(entity instanceof DirtyAware) {DirtyAware dirtyAware = (DirtyAware) entity;Set<String> dirtyProperties = dirtyAware.getDirtyProperties();int[] dirtyPropertiesIndices = new int[dirtyProperties.size()];List<String> propertyNamesList = Arrays.asList(propertyNames);int i = 0;for(String dirtyProperty : dirtyProperties) {LOGGER.info("The {} property is dirty", dirtyProperty);dirtyPropertiesIndices[i++] = propertyNamesList.indexOf(dirtyProperty);}dirtyAware.clearDirtyProperties();return dirtyPropertiesIndices;}return super.findDirty(entity, id, currentState, previousState, propertyNames, types);}}

将此拦截器传递到当前的SessionFactory配置时，我们将获得以下输出：

INFO  [main]: c.v.h.m.l.f.InterceptorDirtyCheckingTest - The number property is dirty
INFO  [main]: c.v.h.m.l.f.InterceptorDirtyCheckingTest - The orderedBy property is dirty
INFO  [main]: c.v.h.m.l.f.InterceptorDirtyCheckingTest - The orderedOn property is dirty
DEBUG [main]: o.h.e.i.AbstractFlushingEventListener - Flushed: 0 insertions, 1 updates, 0 deletions to 1 objects
DEBUG [main]: n.t.d.l.SLF4JQueryLoggingListener - Name: Time:1 Num:1 Query:{[update ORDER_LINE set number=?, orderedBy=?, orderedOn=? where id=?][123,Vlad,2014-08-20 07:35:05.649,1]} 
INFO  [main]: c.v.h.m.l.f.InterceptorDirtyCheckingTest - The orderedBy property is dirty
DEBUG [main]: o.h.e.i.AbstractFlushingEventListener - Flushed: 0 insertions, 1 updates, 0 deletions to 1 objects
DEBUG [main]: n.t.d.l.SLF4JQueryLoggingListener - Name: Time:0 Num:1 Query:{[update ORDER_LINE set number=?, orderedBy=?, orderedOn=? where id=?][123,Alex,2014-08-20 07:35:05.649,1]}

手动脏检查机制已检测到传入更改，并将其传播到刷新事件侦听器。

鲜为人知的CustomEntityDirtinessStrategy

CustomEntityDirtinessStrategy是Hibernate API的新增功能，它使我们能够提供特定于应用程序的脏检查机制。该接口可以实现如下：

public static class EntityDirtinessStrategy implements CustomEntityDirtinessStrategy {@Overridepublic boolean canDirtyCheck(Object entity, EntityPersister persister, Session session) {return entity instanceof DirtyAware;}@Overridepublic boolean isDirty(Object entity, EntityPersister persister, Session session) {return !cast(entity).getDirtyProperties().isEmpty();}@Overridepublic void resetDirty(Object entity, EntityPersister persister, Session session) {cast(entity).clearDirtyProperties();}@Overridepublic void findDirty(Object entity, EntityPersister persister, Session session, DirtyCheckContext dirtyCheckContext) {final DirtyAware dirtyAware = cast(entity);dirtyCheckContext.doDirtyChecking(new AttributeChecker() {@Overridepublic boolean isDirty(AttributeInformation attributeInformation) {String propertyName = attributeInformation.getName();boolean dirty = dirtyAware.getDirtyProperties().contains( propertyName );if (dirty) {LOGGER.info("The {} property is dirty", propertyName);}return dirty;}});}private DirtyAware cast(Object entity) {return DirtyAware.class.cast(entity);}}

要注册CustomEntityDirtinessStrategy实现，我们必须设置以下Hibernate属性：

properties.setProperty("hibernate.entity_dirtiness_strategy", EntityDirtinessStrategy.class.getName());

运行我们的测试将产生以下输出：

INFO  [main]: c.v.h.m.l.f.CustomEntityDirtinessStrategyTest - The number property is dirty
INFO  [main]: c.v.h.m.l.f.CustomEntityDirtinessStrategyTest - The orderedBy property is dirty
INFO  [main]: c.v.h.m.l.f.CustomEntityDirtinessStrategyTest - The orderedOn property is dirty
DEBUG [main]: o.h.e.i.AbstractFlushingEventListener - Flushed: 0 insertions, 1 updates, 0 deletions to 1 objects
DEBUG [main]: n.t.d.l.SLF4JQueryLoggingListener - Name: Time:1 Num:1 Query:{[update ORDER_LINE set number=?, orderedBy=?, orderedOn=? where id=?][123,Vlad,2014-08-20 12:51:30.068,1]} 
INFO  [main]: c.v.h.m.l.f.CustomEntityDirtinessStrategyTest - The orderedBy property is dirty
DEBUG [main]: o.h.e.i.AbstractFlushingEventListener - Flushed: 0 insertions, 1 updates, 0 deletions to 1 objects
DEBUG [main]: n.t.d.l.SLF4JQueryLoggingListener - Name: Time:0 Num:1 Query:{[update ORDER_LINE set number=?, orderedBy=?, orderedOn=? where id=?][123,Alex,2014-08-20 12:51:30.068,1]}