springboot 初始化完成时执行方法，ApplicationListener

ApplicationListener调用过程详解：

实现接口ApplicationListener，并重写public void onApplicationEvent(ApplicationEvent event) {｝可以在容器初始话的时候执行这个方法，其中源码为：

/*
 * Copyright 2002-2016 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;

import java.util.EventListener;

/**
 * Interface to be implemented by application event listeners.
 * Based on the standard {@code java.util.EventListener} interface
 * for the Observer design pattern.
 *
 * <p>As of Spring 3.0, an ApplicationListener can generically declare the event type
 * that it is interested in. When registered with a Spring ApplicationContext, events
 * will be filtered accordingly, with the listener getting invoked for matching event
 * objects only.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @param <E> the specific ApplicationEvent subclass to listen to
 * @see org.springframework.context.event.ApplicationEventMulticaster
 */
@FunctionalInterface
public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {

	/**
	 * Handle an application event.
	 * @param event the event to respond to
	 */
	void onApplicationEvent(E event);

}

事件类型：

1、ApplicationContextEvent

是spring内置事件的父抽象类，构造方法传入spring的context容器，同时也有获取spring的context容器的方法。

2、ContextRefreshedEvent

当spring容器初始化或刷新时，会触发此事件。此事件在开发中常用，用于在spring容器启动时，导入自定义的bean实例到spring容器中。

3、ContextStartedEvent

当spring启动时，或者说是context调用start()方法时，会触发此事件。

4、ContextStoppedEvent

当spring停止时，或者说context调用stop()方法时，会触发此事件。

5、ContextClosedEvent

当spring关闭时，或者说context调用close()方法时，会触发此事件。

 

实际项目中根据需求使用对应事件：

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;

import com.jh.ta.scheduler.Scheduler;

/**
 * <br/>
 * Author:杨杰超<br/>
 * Date:2018年10月28日 下午9:18:05 <br/>
 * Copyright (c) 2018, yangjiechao@dingtalk.com All Rights Reserved.<br/>
 *
 */
public class ApplicationStartup implements ApplicationListener<ContextRefreshedEvent> {

    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        // 初始化完成后. 执行一次同步系统参数
        Scheduler scheduler = contextRefreshedEvent.getApplicationContext().getBean(Scheduler.class);
        scheduler.syncSysParam();
    }
}

可以在ApplicationStartup中添加类注解@Component，让spring容器管理起来。

或者在springboot启动类中手动添加listeners

    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(App.class);
        app.addListeners(new ApplicationStartup());
        app.run(args);
    }

2种方式皆可，