简述 Hibernate 拦截器和事件监听

05 March 2019

Hibernate 作为一个成熟的“ORM”框架，提供了Interceptor和EventListener让应用可以介入和了解它的执行过程。

配置
源码解析

配置

以”Spring Boot”项目(spring-boot-starter-data-jpa-2.1.0.RELEASE)为例:

JpaProperties的properties属性负责存储”JPA”的相关配置，如下所示:

spring.jpa.properties.hibernate.session_factory.interceptor=xx.MyInterceptor
spring.jpa.properties.hibernate.ejb.event.load=xx.MyLoadEventListener

MyLoadEventListener，实现LoadEventListener接口，也就是说可以监听”load”事件。

public class MyLoadEventListener implements LoadEventListener {

    private static final long serialVersionUID = -7776598890958220332L;

    @Override
    public void onLoad(LoadEvent event, LoadType loadType) throws HibernateException {
        System.out.println(event.getEntityClassName());
    }
}

MyInterceptor，实现Interceptor接口，使用时直接继承EmptyInterceptor即可，可根据需求实现对应的方法，本例实现onPrepareStatement方法，即在预编译SQL时会调用该方法(建议使用StatementInspector取代)。

public class MyInterceptor extends EmptyInterceptor {

    private static final long serialVersionUID = 304244397266301266L;

    @Override
    public String onPrepareStatement(String sql) {
        return super.onPrepareStatement(sql);
    }
}

源码解析

SessionFactoryImpl负责解析项目中的相关配置，session创建等，当然也包括 Interceptor 和 EventListener。

SessionFactoryImpl的内部类SessionBuilderImpl的configuredInterceptor方法创建”interceptor”，其中具体的解析操作由SessionFactoryOptionsBuilder(SessionFactoryOptions)完成。

public static Interceptor configuredInterceptor(Interceptor interceptor, SessionFactoryOptions options) {
    // NOTE : DO NOT return EmptyInterceptor.INSTANCE from here as a "default for the Session"
    // 		we "filter" that one out here.  The return from here should represent the
    //		explicitly configured Interceptor (if one).  Return null from here instead; Session
    //		will handle it

    if ( interceptor != null && interceptor != EmptyInterceptor.INSTANCE ) {
        return interceptor;
    }

    // prefer the SF-scoped interceptor, prefer that to any Session-scoped interceptor prototype
    if ( options.getInterceptor() != null && options.getInterceptor() != EmptyInterceptor.INSTANCE ) {
        return options.getInterceptor();
    }

    // then check the Session-scoped interceptor prototype
    if ( options.getStatelessInterceptorImplementor() != null && options.getStatelessInterceptorImplementorSupplier() != null ) {
        throw new HibernateException(
                "A session scoped interceptor class or supplier are allowed, but not both!" );
    }
    else if ( options.getStatelessInterceptorImplementor() != null ) {
        try {
            /**
                * We could remove the getStatelessInterceptorImplementor method and use just the getStatelessInterceptorImplementorSupplier
                * since it can cover both cases when the user has given a Supplier<? extends Interceptor> or just the
                * Class<? extends Interceptor>, in which case, we simply instantiate the Interceptor when calling the Supplier.
                */
            return options.getStatelessInterceptorImplementor().newInstance();
        }
        catch (InstantiationException | IllegalAccessException e) {
            throw new HibernateException( "Could not supply session-scoped SessionFactory Interceptor", e );
        }
    }
    else if ( options.getStatelessInterceptorImplementorSupplier() != null ) {
        return options.getStatelessInterceptorImplementorSupplier().get();
    }

    return null;
}

SessionFactoryImpl的构造方法通过调用prepareEventListeners方法创建配置的”EventListener”。

private void prepareEventListeners(MetadataImplementor metadata) {
    final EventListenerRegistry eventListenerRegistry = serviceRegistry.getService( EventListenerRegistry.class );
    final ConfigurationService cfgService = serviceRegistry.getService( ConfigurationService.class );
    final ClassLoaderService classLoaderService = serviceRegistry.getService( ClassLoaderService.class );

    eventListenerRegistry.prepare( metadata );

    for ( Map.Entry entry : ( (Map<?, ?>) cfgService.getSettings() ).entrySet() ) {
        if ( !String.class.isInstance( entry.getKey() ) ) {
            continue;
        }
        final String propertyName = (String) entry.getKey();
        if ( !propertyName.startsWith( org.hibernate.jpa.AvailableSettings.EVENT_LISTENER_PREFIX ) ) {
            continue;
        }
        final String eventTypeName = propertyName.substring(
                org.hibernate.jpa.AvailableSettings.EVENT_LISTENER_PREFIX.length() + 1
        );
        final EventType eventType = EventType.resolveEventTypeByName( eventTypeName );
        final EventListenerGroup eventListenerGroup = eventListenerRegistry.getEventListenerGroup( eventType );
        for ( String listenerImpl : ( (String) entry.getValue() ).split( " ," ) ) {
            eventListenerGroup.appendListener( instantiate( listenerImpl, classLoaderService ) );
        }
    }
}

其中，配置可参考以下类，它们定义了可配置项。

org.hibernate.jpa.AvailableSettings
org.hibernate.cfg.AvailableSettings
org.hibernate.cfg.Environment

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