Observer mode -- ApplicationContext

One 、 Observer mode definition ：

Refers to the existence of one to many dependencies among multiple objects , When the state of an object changes , All objects that depend on it are notified and automatically updated . This pattern is sometimes called Publishing - A subscription model 、 Model - View mode , It's an object behavior pattern

advantage ：

1. It reduces the coupling between the target and the observer , There is an abstract coupling between the two . It conforms to the principle of dependency inversion .
2. There is a trigger mechanism between the target and the observer .

shortcoming ：

1. The dependence between the target and the observer is not completely relieved , And it's possible to have circular references .
2. When there are many observers , The announcement conference took a lot of time , Affect the efficiency of the program .

Two 、 spring in ApplicationContext An example of an application observer is as follows ：

import javax.annotation.Resource;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.ApplicationContext;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@Slf4j
@RestController
public class Test1Controller {

    @Resource
    private ApplicationContext applicationContext;

    @GetMapping(value = "/test")
    public void test(){
        String message = " Xiao Li, your black s The needle doesn't poke , Come to my office ";
        applicationContext.publishEvent(new TestEvent(this,message));
    }

}

import lombok.Getter;
import org.springframework.context.ApplicationEvent;

@Getter
public class TestEvent extends ApplicationEvent {

	private final String message;

	public TestEvent(Object source, String message){
		super(source);
		this.message = message;
	}

}

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class TestEventListener {

    @EventListener
    public void receiveMessage(TestEvent testEvent){
        System.out.print(testEvent.getMessage());
    }
}

A simple code for you , Official account will be developed later. , If you have any questions, please add me wechat , Learning together ～