06. Spring中的事件监听器

一 概念

1. Spring中的事件监听

在一个Spring容器中，我们可以发送消息给Spring容器，容器收到消息后自动接受消息并进行处理

事件监听主要有两部分组成，一个是事件源，另一个是监听事件并处理的对象

使用的时候，我们只需要自定义事件继承事件对象ApplicationEvent，自定义监听器实现监听器ApplicationListener，并将监听器注册到Spring容器中即可

1.1 事件

Spring事件对象为ApplicationEvent，继承自ObjectEvent

public abstract class ApplicationEvent extends EventObject {

	/**
	 * Create a new ApplicationEvent.
	 * 创建一个新的应用事件对象
	 * @param source the object on which the event initially occurred (never {@code null})
	 */
	public ApplicationEvent(Object source) {
		super(source);
		this.timestamp = System.currentTimeMillis();
	}
}

1.2 事件监听器

当事件对象被发布到Spring中的监听器，将会找出对应的监听器对事件进行处理

Spring中的事件监听器为ApplicationListener，继承自EventListener

public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {
    void onApplicationEvent(E var1);
}

二. Spring使用方式

创建事件对象

public class MyApplicationEvent extends ApplicationEvent {
    public MyApplicationEvent(Object source) {
        super(source);
    }
}

创建监听器

public class MyApplicationListener implements ApplicationListener<MyApplicationEvent> {
    @Override
    public void onApplicationEvent(MyApplicationEvent event) {
        System.out.println("收到事件：" + event);
    }
}

注册监听器

public class ApplicationEventBootstrap {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context =
                new AnnotationConfigApplicationContext();
        // 注册自定义事件监听器
        context.addApplicationListener(new MyApplicationListener());
        // 启动上下文
        context.refresh();
        // 发布事件
        context.publishEvent(new MyApplicationEvent(context));
        // 结束
        context.close();
    }
}

三 SpringBoot中的推荐使用方式

1. 事件对象继承ApplicationEvent、事件监听器实现ApplicationListener

举例：浙商资产管理中预警事件

Event

public class WarningEvent extends ApplicationEvent {

    private Map<String,String> content;

    /**
     * Create a new {@code ApplicationEvent}.
     *
     * @param source the object on which the event initially occurred or with
     *               which the event is associated (never {@code null})
     */
    public WarningEvent(Object source) {
        super(source);
    }

    public WarningEvent(Object source, Map<String,String> content) {
        super(source);
        this.content = content;
    }

    public  Map<String,String> getContent() {
        return content;
    }

    public void setContent( Map<String,String> content) {
        this.content = content;
    }
}

Listener

@Slf4j
@Component // 将监听器交给Spring容器管理
public class WarningListener implements ApplicationListener<WarningEvent> {
    
    @Override
    public void onApplicationEvent(WarningEvent event) {
        // do something
    }

}

Test：伪代码，重点在于使用WebApplicationContext容器发布消息

@Component
public class TestEvent{
	@Autowired
    private WebApplicationContext webApplicationContext;

 Map<String,String> params3 = new HashMap<>();
                params3.put("deviceName",deviceName);
                params3.put("deviceSerial",deviceSerial);
                params3.put("url",picUrl);
                params2.put("url",picUrl);
                WarningEvent event = new WarningEvent("object",params3);
                webApplicationContext.publishEvent(event);

}

2. 使用@EventListener注解实现

实现方式：

1. 自定义Event事件对象继承ApplicationEvent
2. 使用类似BeanConfig类的方式，用@EventListener注解声明监听器

事件对象

public class WarningEvent extends ApplicationEvent {

    private Map<String,String> content;

    /**
     * Create a new {@code ApplicationEvent}.
     *
     * @param source the object on which the event initially occurred or with
     *               which the event is associated (never {@code null})
     */
    public WarningEvent(Object source) {
        super(source);
    }

    public WarningEvent(Object source, Map<String,String> content) {
        super(source);
        this.content = content;
    }

    public  Map<String,String> getContent() {
        return content;
    }

    public void setContent( Map<String,String> content) {
        this.content = content;
    }
}

注册监听器

@Component // 也要把该类交给Spring容器管理
public class ListenerConfig{
    
    @Listener(WarningEvent.class) // 标明监听的哪个事件
    public void onEvent(WarnEvent event){
        Object source = event.getSouce();
        // do something
    }
}

发布事件

@Component
public class TestEvent{
	@Autowired
    private WebApplicationContext webApplicationContext;

 Map<String,String> params3 = new HashMap<>();
                params3.put("deviceName",deviceName);
                params3.put("deviceSerial",deviceSerial);
                params3.put("url",picUrl);
                params2.put("url",picUrl);
                WarningEvent event = new WarningEvent("object",params3);
                webApplicationContext.publishEvent(event);

}

3. 使用ConfigurableApplicationContext装载监听

public class MyListener1 implements ApplicationListener<MyEvent>
{
	Logger logger = Logger.getLogger(MyListener1.class);
	
	public void onApplicationEvent(MyEvent event)
	{
		logger.info(String.format("%s监听到事件源：%s.", MyListener1.class.getName(), event.getSource()));
	}
}

@SpringBootApplication
public class LisenterApplication
{
	public static void main(String[] args)
	{
		ConfigurableApplicationContext context = SpringApplication.run(LisenterApplication.class, args);
		//装载监听，完成
		context.addApplicationListener(new MyListener1());
	}
}