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Definition:

The Observer pattern is a behavioral design pattern that allows you to define a subscription mechanism to notify multiple other objects that “observe” an object when an event occurs on that object.

Practical requirements:

After the consumer leaves a message in the system, the system administrator needs to be notified by the information in the system station and the administrator needs to be notified by email

Code:

Message entity class: CustomerLeaveMessage. Java

public class CustomerLeaveMessage implements Serializable { private static final long serialVersionUID = 1L; private String id; Private String name; // Private String phone; Private String email; // Contact email private String content; }Copy the code

Create a new Event, inherit ApplicationEvent and pass a CustomerLeaveMessage parameter to the business logic:

/ * * * @ the author frequently the wind * * consumer message events @ the date 2021-07-16 14:26 * / public class CustomerLeaveMessageEvent extends ApplicationEvent  { public CustomerLeaveMessageEvent(CustomerLeaveMessage source) { super(source); }}Copy the code

At this point, there are two ways to implement the listener: one is to implement the ApplicationListener interface, and the other is to implement the annotation using @EventListener

  1. Implement the ApplicationListener interface

/ * * * listening CustomerLeaveMessageEvent logic * @ the author frequently after the wind * @ the date comes to 2021-07-16 * / @ Slf4j @ Service public class CustomerLeaveMessageEventService implements ApplicationListener < CustomerLeaveMessageEvent > {/ * * * after execution monitoring logic * @ param CustomerLeaveMessageEvent * / @ Override @ Async / / asynchronous public void onApplicationEvent (customerLeaveMessageEvent CustomerLeaveMessageEvent) {log. The info (" user comments after logical response, on-site notice sending to an administrator: {} ", customerLeaveMessageEvent. The toString ()); }}Copy the code

  1. This is done by annotating @eventListener.

@Service @Slf4j public class CustomerLeaveMessageEventListener { @EventListener public void SendEmail (CustomerLeaveMessageEvent event) {the info (" sends E-mail to the administrator "); }}Copy the code

Finally use in service:

(1) Inject ApplicationContext
@Autowired
private ApplicationContext applicationContext;
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(2) Then append the statement to the logic behind the customer message
applicationContext.publishEvent(new CustomerLeaveMessageEvent(customerLeaveMessage));
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