009-Spring Boot 事件监听

一、概念

1.事件监听的流程

　　步骤一、自定义事件，一般是继承ApplicationEvent抽象类

　　步骤二、定义事件监听器，一般是实现ApplicationListener接口

　　步骤三、启动时，需要将监听器加入到Spring容器中

　　步骤四、发布事件

对于配置监听器的方式【即第三步】

　　方式一、app.addListeners(new MyApplicationListener());添加监听器

　　方式二、把监听器使用纳入Spring配置中管理如使用@Component标注

　　方式三、再application.properties中添加context.listener.classes配置项配置

　　方式四、使用注解@EventListener在方法上，且该类需要在Spring上管理

2、示例【方式一】：

步骤一、自定义事件MyApplicationEvent

package com.lhx.spring.springboot_event;

import org.springframework.context.ApplicationEvent;

/**
 * 定义事件
 * @author Administrator
 *
 */
public class MyApplicationEvent extends ApplicationEvent {
    private static final long serialVersionUID = 1L;

    public MyApplicationEvent(Object source) {
        super(source);
    }
}

步骤二、定义事件监听器MyApplicationListener

package com.lhx.spring.springboot_event;

import org.springframework.context.ApplicationListener;

public class MyApplicationListener implements ApplicationListener<MyApplicationEvent> {

    @Override
    public void onApplicationEvent(MyApplicationEvent event) {
        System.out.println("接收到事件:" + event.getClass());
    }

}

步骤三、在App启动程序中添加以及发布

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        // ConfigurableApplicationContext context = SpringApplication.run(App.class,
        // args);
        SpringApplication app = new SpringApplication(App.class);
        app.addListeners(new MyApplicationListener());
        ConfigurableApplicationContext context = app.run(args);
        context.publishEvent(new MyApplicationEvent(new Object()));
        context.close();
    }
}

3、示例【方式二】：

注意：其实在示例步骤三，也可以用注解方式将时间监听器纳入Spring管理中

步骤一、与示例一一致

步骤二、将事件监听器添加@Component注解。

步骤三、启动类

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(App.class);
        //app.addListeners(new MyApplicationListener());
        ConfigurableApplicationContext context = app.run(args);
        context.publishEvent(new MyApplicationEvent(new Object()));
        context.close();
    }
}

4、示例【方式四】：

步骤一、与示例一一致

步骤二、与示例一一致

步骤三、增加单独处理类

package com.lhx.spring.springboot_event;

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

@Component
public class MyEventHandle {
    @EventListener
    public void event(MyApplicationEvent event) {
        System.out.println("MyEventHandle 接收到事件:" + event.getClass());
    }

    @EventListener
    public void event2(ContextStoppedEvent event) {
        System.out.println("应用停止  接收到事件:" + event.getClass());
    }
}

步骤三、启动类

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(App.class);、
        ConfigurableApplicationContext context = app.run(args);
        context.publishEvent(new MyApplicationEvent(new Object()));
        context.close();
    }
}

二、配置监听器的方式原理

1.方式三实现，在application.properties中添加context.listener.classes配置项配置

查看：DelegatingApplicationListener

public class DelegatingApplicationListener
        implements ApplicationListener<ApplicationEvent>, Ordered {

    // NOTE: Similar to org.springframework.web.context.ContextLoader

    private static final String PROPERTY_NAME = "context.listener.classes";

核心逻辑

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            List<ApplicationListener<ApplicationEvent>> delegates = getListeners(
                    ((ApplicationEnvironmentPreparedEvent) event).getEnvironment());
            if (delegates.isEmpty()) {
                return;
            }
            this.multicaster = new SimpleApplicationEventMulticaster();
            for (ApplicationListener<ApplicationEvent> listener : delegates) {
                this.multicaster.addApplicationListener(listener);
            }
        }
        if (this.multicaster != null) {
            this.multicaster.multicastEvent(event);
        }
    }

    @SuppressWarnings("unchecked")
    private List<ApplicationListener<ApplicationEvent>> getListeners(
            ConfigurableEnvironment environment) {
        if (environment == null) {
            return Collections.emptyList();
        }
        String classNames = environment.getProperty(PROPERTY_NAME);
        List<ApplicationListener<ApplicationEvent>> listeners = new ArrayList<ApplicationListener<ApplicationEvent>>();
        if (StringUtils.hasLength(classNames)) {
            for (String className : StringUtils.commaDelimitedListToSet(classNames)) {
                try {
                    Class<?> clazz = ClassUtils.forName(className,
                            ClassUtils.getDefaultClassLoader());
                    Assert.isAssignable(ApplicationListener.class, clazz, "class ["
                            + className + "] must implement ApplicationListener");
                    listeners.add((ApplicationListener<ApplicationEvent>) BeanUtils
                            .instantiateClass(clazz));
                }
                catch (Exception ex) {
                    throw new ApplicationContextException(
                            "Failed to load context listener class [" + className + "]",
                            ex);
                }
            }
        }
        AnnotationAwareOrderComparator.sort(listeners);
        return listeners;
    }

2、方式四实现

查看：EventListenerMethodProcessor的processBean

    protected void processBean(final List<EventListenerFactory> factories, final String beanName, final Class<?> targetType) {
        if (!this.nonAnnotatedClasses.contains(targetType)) {
            Map<Method, EventListener> annotatedMethods = null;
            try {
                annotatedMethods = MethodIntrospector.selectMethods(targetType,
                        new MethodIntrospector.MetadataLookup<EventListener>() {
                            @Override
                            public EventListener inspect(Method method) {
                                return AnnotatedElementUtils.findMergedAnnotation(method, EventListener.class);
                            }
                        });
            }
            catch (Throwable ex) {
                // An unresolvable type in a method signature, probably from a lazy bean - let‘s ignore it.
                if (logger.isDebugEnabled()) {
                    logger.debug("Could not resolve methods for bean with name ‘" + beanName + "‘", ex);
                }
            }
            if (CollectionUtils.isEmpty(annotatedMethods)) {
                this.nonAnnotatedClasses.add(targetType);
                if (logger.isTraceEnabled()) {
                    logger.trace("No @EventListener annotations found on bean class: " + targetType.getName());
                }
            }
            else {
                // Non-empty set of methods
                for (Method method : annotatedMethods.keySet()) {
                    for (EventListenerFactory factory : factories) {
                        if (factory.supportsMethod(method)) {
                            Method methodToUse = AopUtils.selectInvocableMethod(
                                    method, this.applicationContext.getType(beanName));
                            ApplicationListener<?> applicationListener =
                                    factory.createApplicationListener(beanName, targetType, methodToUse);
                            if (applicationListener instanceof ApplicationListenerMethodAdapter) {
                                ((ApplicationListenerMethodAdapter) applicationListener)
                                        .init(this.applicationContext, this.evaluator);
                            }
                            this.applicationContext.addApplicationListener(applicationListener);
                            break;
                        }
                    }
                }
                if (logger.isDebugEnabled()) {
                    logger.debug(annotatedMethods.size() + " @EventListener methods processed on bean ‘" +
                            beanName + "‘: " + annotatedMethods);
                }
            }
        }
    }

EventListener

                annotatedMethods = MethodIntrospector.selectMethods(targetType,
                        new MethodIntrospector.MetadataLookup<EventListener>() {
                            @Override
                            public EventListener inspect(Method method) {
                                return AnnotatedElementUtils.findMergedAnnotation(method, EventListener.class);
                            }
                        });

查看for

                for (Method method : annotatedMethods.keySet()) {
                    for (EventListenerFactory factory : factories) {
                        if (factory.supportsMethod(method)) {
                            Method methodToUse = AopUtils.selectInvocableMethod(
                                    method, this.applicationContext.getType(beanName));
                            ApplicationListener<?> applicationListener =
                                    factory.createApplicationListener(beanName, targetType, methodToUse);
                            if (applicationListener instanceof ApplicationListenerMethodAdapter) {
                                ((ApplicationListenerMethodAdapter) applicationListener)
                                        .init(this.applicationContext, this.evaluator);
                            }
                            this.applicationContext.addApplicationListener(applicationListener);
                            break;
                        }
                    }
                }

其中factory即EventListenerFactory factory

/*
 * Copyright 2002-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.event;

import java.lang.reflect.Method;

import org.springframework.context.ApplicationListener;

/**
 * Strategy interface for creating {@link ApplicationListener} for methods
 * annotated with {@link EventListener}.
 *
 * @author Stephane Nicoll
 * @since 4.2
 */
public interface EventListenerFactory {

    /**
     * Specify if this factory supports the specified {@link Method}.
     * @param method an {@link EventListener} annotated method
     * @return {@code true} if this factory supports the specified method
     */
    boolean supportsMethod(Method method);

    /**
     * Create an {@link ApplicationListener} for the specified method.
     * @param beanName the name of the bean
     * @param type the target type of the instance
     * @param method the {@link EventListener} annotated method
     * @return an application listener, suitable to invoke the specified method
     */
    ApplicationListener<?> createApplicationListener(String beanName, Class<?> type, Method method);

}

三、spring、Spring boot内置事件

1.Spring

jar包：Spring-context-4.3.13.RELEASE

　　包：org.springframwork.context.event;

常用：ContextClosedEvent、ContextStartedEvent、ContextStopedEvent

示例

@Component
public class MyEventHandle {
    @EventListener
    public void event2(ContextStoppedEvent event) {
        System.out.println("应用停止  接收到事件:" + event.getClass());
    }
}

当然：app中Context要停止

@SpringBootApplication
public class App {
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(App.class);
        ConfigurableApplicationContext context = app.run(args);
        context.publishEvent(new MyApplicationEvent(new Object()));
        context.stop();
    }
}

2.Spring-boot

jar包：Spring-boot-1.5.9.RELEASE

　　包：org.springframework.boot.context.event;

常用：ApplicationEnvironmentPreparedEvent、ApplicationFailedEvent等

原文地址：https://www.cnblogs.com/bjlhx/p/8343855.html

时间： 2024-08-11 01:19:56

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