spring中的事件 applicationevent 讲的确实不错（转）

event，listener是observer模式一种体现，在spring 3.0.5中，已经可以使用annotation实现event和eventListner里。
我们以spring-webflow里的hotel booking为例，看一下实现，步骤如下：
1，建立event

public class BookingCreatedEvent extends ApplicationEvent {
 private static final long serialVersionUID = 3039313222160544111L; private Booking booking; public BookingCreatedEvent(Object source) { super(source); } public BookingCreatedEvent(Object source, Booking booking) { super(source); this.booking = booking; } public Booking getBooking() { return booking; } }

 
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event需要继承ApplicationEvent。

2，建立listener

@Component
public class BookingEventsListener implements ApplicationListener<BookingCreatedEvent> {
 private static final Logger log = Logger.getLogger(); //listener实现 public void onApplicationEvent(BookingCreatedEvent event) { log.debug("bookingId:" + event.getBooking().getId()); //do something  } }

 
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listener需要实现ApplicationListener。
注意在spring 3.0.5中的ApplicationListener是带泛型的，这样BookingEventsListener只会监听BookingCreatedEvent事件。
另外可以用@Component来注册组件，这样就不需要在spring的配置文件中指定了。

3，触发event

@Service("bookingService")
@Repository
public class JpaBookingService implements BookingService, ApplicationContextAware {

 private ApplicationContext context; public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { log.debug("Autowired applicationContext"); this.context = applicationContext; } //省略的代码  @Transactional public void persistBooking(Booking booking) throws HibernateException, SQLException { em.persist(booking); log.debug("fire BookingCreatedEvent"); BookingCreatedEvent bookingCreatedEvent = new BookingCreatedEvent(this, booking); //触发event this.context.publishEvent(bookingCreatedEvent); } }

 
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触发要实现ApplicationContextAware，用于引入ApplicationContext，由于bookingService也是spring组件，所以在系统启动的时候，ApplicationContext已经注入。也可以用如下方式直接注入 ApplicationContext。

@Autowired
private ApplicationContext applicationContext;

 
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那么event listener这种模式的好处是什么呢？举个例子，如果客人booking了hotel以后，系统要发email给客人，那我们就可以在listener的do something处加入发送email的代码。
上面我们讲起用@Component把listener注册成了spring的组件，这样listener的用途是在runtime的时候解耦。
而如果我们把listener用配置文件的方式注册的话，主要的用途是在部署时解耦。
在实际应用中，两种情况都有。

另外要注意的一点是，service和listener是同步的，在service中的persistBooking有注册 @Transactional的情况下，listener中的do something和service中的persistBooking是在同一个tansaction下。
如果要做异步，需要通过MQ或者数据库中转。

public class BookingCreatedEvent extends ApplicationEvent {
 private static final long serialVersionUID = 3039313222160544111L; private Booking booking; public BookingCreatedEvent(Object source) { super(source); } public BookingCreatedEvent(Object source, Booking booking) { super(source); this.booking = booking; } public Booking getBooking() { return booking; } }

 
        <code  
        class 
        = 
        "hljs java" 
        ><span  
        class 
        = 
        "hljs-keyword" 
        > </span></code>

event需要继承ApplicationEvent。

2，建立listener

@Component
public class BookingEventsListener implements ApplicationListener<BookingCreatedEvent> {
 private static final Logger log = Logger.getLogger(); //listener实现 public void onApplicationEvent(BookingCreatedEvent event) { log.debug("bookingId:" + event.getBooking().getId()); //do something  } }

 
        <code  
        class 
        = 
        "hljs java" 
        ><span  
        class 
        = 
        "hljs-meta" 
        ><span style= 
        "background-color: #ff6600; color: #99cc00;" 
        > </span></span></code>

3，触发event

@Service("bookingService")
@Repository
public class JpaBookingService implements BookingService, ApplicationContextAware {

 private ApplicationContext context; public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { log.debug("Autowired applicationContext"); this.context = applicationContext; } //省略的代码  @Transactional public void persistBooking(Booking booking) throws HibernateException, SQLException { em.persist(booking); log.debug("fire BookingCreatedEvent"); BookingCreatedEvent bookingCreatedEvent = new BookingCreatedEvent(this, booking); //触发event this.context.publishEvent(bookingCreatedEvent); } }

 
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@Autowired
private ApplicationContext applicationContext;

 
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        > </code>

spring中的事件 applicationevent 讲的确实不错（转）

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