org.springframework.context.ApplicationListener<ApplicationReadyEvent>

**
 * 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
 */
public interface ApplicationListener<E extends ApplicationEvent> extends EventListener

在一些业务场景中，当容器初始化完成之后，需要处理一些操作，比如一些数据的加载、初始化缓存、特定任务的注册，加载权限，菜单到redis，执行监听的job等等。这个时候我们就可以使用Spring提供的ApplicationListener来进行操作。

实现ApplicationListener接口并实现onApplicationEvent方法。把需要处理的操作放在onApplicationEvent中进行处理

@Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        System.out.println("我的父容器为：" + contextRefreshedEvent.getApplicationContext().getParent());
        System.out.println("初始化时我被调用了。");
    }

使用Spring boot来进行操作，没有出现二次调用的问题。在使用传统的application.xml和project-servlet.xml配置中会出现二次调用的问题。主要原因是初始化root容器之后，会初始化project-servlet.xml对应的子容器。我们需要的是只执行一遍即可。那么上面打印父容器的代码用来进行判断排除子容器即可。在业务处理之前添加如下判断：

if(contextRefreshedEvent.getApplicationContext().getParent() != null){
            return;
}

代替写法为：

InitializingBean:spring 容器初始化之前执行

org.springframework.beans.factory.InitializingBean

/**
 * Interface to be implemented by beans that need to react once all their
 * properties have been set by a BeanFactory: for example, to perform custom
 * initialization, or merely to check that all mandatory properties have been set.
 *
 * <p>An alternative to implementing InitializingBean is specifying a custom
 * init-method, for example in an XML bean definition.
 * For a list of all bean lifecycle methods, see the BeanFactory javadocs.
 *
 * @author Rod Johnson
 * @see BeanNameAware
 * @see BeanFactoryAware
 * @see BeanFactory
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
 * @see org.springframework.context.ApplicationContextAware
 */
public interface InitializingBean

@Override
    public void afterPropertiesSet() throws Exception {
        loadParams();
        loadConfig();
    }

org.springframework.context.ApplicationListener<ApplicationReadyEvent>

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