spring boot实战(第二篇)事件监听

spring boot实战(第二篇)事件监听

前言

spring boot在启动过程中增加事件监听机制，为用户功能拓展提供极大的便利。

支持的事件类型四种

ApplicationStartedEvent

ApplicationEnvironmentPreparedEvent

ApplicationPreparedEvent

ApplicationFailedEvent

实现监听步骤：

1.监听类实现ApplicationListener接口 
2.将监听类添加到SpringApplication实例

ApplicationStartedEvent

ApplicationStartedEvent：spring boot启动开始时执行的事件

创建对应的监听类 MyApplicationStartedEventListener.java

package com.lkl.springboot.listener;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.ApplicationListener;

/**
 * spring boot 启动监听类
 * 
 * @author liaokailin
 * @version $Id: MyApplicationStartedEventListener.java, v 0.1 2015年9月2日 下午11:06:04 liaokailin Exp $
 */
public class MyApplicationStartedEventListener implements ApplicationListener<ApplicationStartedEvent> {

    private Logger logger = LoggerFactory.getLogger(MyApplicationStartedEventListener.class);

    @Override
    public void onApplicationEvent(ApplicationStartedEvent event) {
        SpringApplication app = event.getSpringApplication();
        app.setShowBanner(false);// 不显示banner信息
        logger.info("==MyApplicationStartedEventListener==");
    }
}

• 
  

在该事件中可以获取到SpringApplication对象，可做一些执行前的设置.

Application.java类

package com.lkl.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import com.lkl.springboot.listener.MyApplicationStartedEventListener;

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(Application.class); 
        app.addListeners(new MyApplicationStartedEventListener());
        app.run(args);
    }

ApplicationEnvironmentPreparedEvent

ApplicationEnvironmentPreparedEvent：spring boot 对应Enviroment已经准备完毕，但此时上下文context还没有创建。

MyApplicationEnvironmentPreparedEventListener.java

package com.lkl.springboot.listener;

import java.util.Iterator;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.MutablePropertySources;
import org.springframework.core.env.PropertySource;

/**
 * spring boot 配置环境事件监听
 * @author liaokailin
 * @version $Id: MyApplicationEnvironmentPreparedEventListener.java, v 0.1 2015年9月2日 下午11:21:15 liaokailin Exp $
 */
public class MyApplicationEnvironmentPreparedEventListener implements
                                                          ApplicationListener {
    private Logger logger = LoggerFactory.getLogger(MyApplicationEnvironmentPreparedEventListener.class);

    @Override
    public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {

        ConfigurableEnvironment envi = event.getEnvironment();
        MutablePropertySources mps = envi.getPropertySources();
        if (mps != null) {
            Iterator> iter = mps.iterator();
            while (iter.hasNext()) {
                PropertySource ps = iter.next();
                logger
                    .info("ps.getName:{};ps.getSource:{};ps.getClass:{}", ps.getName(), ps.getSource(), ps.getClass());
            }
        }
    }

}

• 
  

在该监听中获取到ConfigurableEnvironment后可以对配置信息做操作，例如：修改默认的配置信息，增加额外的配置信息等等~~~

ApplicationPreparedEvent

ApplicationPreparedEvent:spring boot上下文context创建完成，但此时spring中的bean是没有完全加载完成的。

MyApplicationPreparedEventListener.java

package com.lkl.springboot.listener;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.context.event.ApplicationPreparedEvent;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.ConfigurableApplicationContext;

/**
 * 上下文创建完成后执行的事件监听器
 * 
 * @author liaokailin
 * @version $Id: MyApplicationPreparedEventListener.java, v 0.1 2015年9月2日 下午11:29:38 liaokailin Exp $
 */
public class MyApplicationPreparedEventListener implements ApplicationListener<ApplicationPreparedEvent> {
    private Logger logger = LoggerFactory.getLogger(MyApplicationPreparedEventListener.class);

    @Override
    public void onApplicationEvent(ApplicationPreparedEvent event) {
        ConfigurableApplicationContext cac = event.getApplicationContext();
        passContextInfo(cac);
    }

    /**
     * 传递上下文
     * @param cac
     */
    private void passContextInfo(ApplicationContext cac) {
        //dosomething()
    }

}

• 
  

在获取完上下文后，可以将上下文传递出去做一些额外的操作。

在该监听器中是无法获取自定义bean并进行操作的。

ApplicationFailedEvent

ApplicationFailedEvent:spring boot启动异常时执行事件 
MyApplicationFailedEventListener.java

package com.lkl.springboot.listener;

import org.springframework.boot.context.event.ApplicationFailedEvent;
import org.springframework.context.ApplicationListener;

public class MyApplicationFailedEventListener implements ApplicationListener<ApplicationFailedEvent> {

    @Override
    public void onApplicationEvent(ApplicationFailedEvent event) {
        Throwable throwable = event.getException();
        handleThrowable(throwable);
    }

    /*处理异常*/
    private void handleThrowable(Throwable throwable) {
    }

}

• 
  

在异常发生时，最好是添加虚拟机对应的钩子进行资源的回收与释放，能友善的处理异常信息。

在spring boot中已经为大家考虑了这一点，默认情况开启了对应的功能：

public void registerShutdownHook() {
        if (this.shutdownHook == null) {
            // No shutdown hook registered yet.
            this.shutdownHook = new Thread() {
                @Override
                public void run() {
                    doClose();
                }
            };
            Runtime.getRuntime().addShutdownHook(this.shutdownHook);
        }
    }

• 
  
• 
  

在doClose()方法中进行资源的回收与释放。

结束语

spring boot提供的四种监听事件到这里就结束了，针对实际业务可添加自定义的监听器，下一节当中将会对spring boot中的监听源码进行分析，理解为什么是这样的。

spring boot监听器使用

   分享牛   2017-04-18   4124℃

摘要：spring boot提供了一系列的监听器，方便我们开发人员使用和扩展。

本文咱们详细讲解一下spring boot中的监听器。

spring boot中支持的事件类型定在org.springframework.boot.context.event包中，目前支持的事件类型有如下6种：

1. ApplicationFailedEvent

2. ApplicationPreparedEvent

3. ApplicationReadyEvent

4. ApplicationStartedEvent

5. SpringApplicationEvent

6. ApplicationEnvironmentPreparedEvent

监听器的使用

第一：首先定义一个自己使用的监听器类并实现ApplicationListener接口。

第二：通过SpringApplication类中的addListeners方法将自定义的监听器注册进去。

ApplicationFailedEvent

ApplicationFailedEvent：该事件为spring boot启动失败时的操作

/**
* spring boot 启动的时候出现异常事件
* @author www.shareniu.com
*
*/
public class ShareniuApplicationFailedEventListener implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationFailedEvent event) {
System.out.println("--------------:ShareniuApplicationFailedEventListener");
Throwable exception = event.getException();
System.out.println(exception);
}
}

可以通过ApplicationFailedEvent 获取Throwable实例对象获取异常信息并处理。

ApplicationPreparedEvent

ApplicationPreparedEvent：上下文准备事件。

上下文context已经准备完毕 ，可以通过ApplicationPreparedEvent获取到ConfigurableApplicationContext实例对象。ConfigurableApplicationContext类继承ApplicationContext类，但需要注意这个时候spring容器中的bean还没有被完全的加载，因此如果通过ConfigurableApplicationContext获取bean会报错的。比如报错：

Exception in thread "main" java.lang.IllegalStateException: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@69b0fd6f has not been refreshed yet

获取到上下文之后，可以将其注入到其他类中，毕竟ConfigurableApplicationContext为引用类型

public class ShareniuApplicationPreparedEventListener implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationPreparedEvent event) {
System.out.println("###############"+"ShareniuApplicationPreparedEventListener");
ConfigurableApplicationContext applicationContext = event.getApplicationContext();
//如果执行下面代码则报错
//ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);
//System.out.println(shareniuDemo);
}
}

ApplicationReadyEvent

ApplicationReadyEvent：上下文已经准备ok。

这个时候就可以通过ApplicationReadyEvent获取ConfigurableApplicationContext，然后通过ConfigurableApplicationContext 获取bean的信息。

public class ShareniuApplicationReadyEventListener implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationReadyEvent event) {
System.out.println("--------------------:ShareniuApplicationReadyEventListener");
ConfigurableApplicationContext applicationContext = event.getApplicationContext();
//ShareniuDemo可以根基自身情况进行测试
ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);
}
}

ApplicationStartedEvent

ApplicationStartedEvent：spring boot 启动监听类。

可以在SpringApplication启动之前做一些手脚，比如修改SpringApplication实例对象中的属性值

public class ShareniuApplicationStartedEventListener  implements ApplicationListener{
@Override
public void onApplicationEvent(ApplicationStartedEvent event) {
SpringApplication springApplication = event.getSpringApplication();
springApplication.setShowBanner(false);
System.out.println("##############################ShareniuApplicationStartedEventListener");
}
}

SpringApplicationEvent

SpringApplicationEvent：获取SpringApplication

public class ShareniuSpringApplicationEventListener implements ApplicationListener {
@Override
public void onApplicationEvent(SpringApplicationEvent event) {
System.out.println("-----------------------:ShareniuSpringApplicationEventListener");
SpringApplication springApplication = event.getSpringApplication();
System.out.println("###############"+springApplication);
}
}

ApplicationEnvironmentPreparedEvent

ApplicationEnvironmentPreparedEvent：环境事先准备，spring boot中的环境已经准备ok

可以通过ApplicationEnvironmentPreparedEvent获取到SpringApplication、ConfigurableEnvironment等等信息， 可以通过ConfigurableEnvironment实例对象来修改以及获取默认的环境信息。

public class ShasreniuApplicationEnvironmentPreparedEventListener  implements ApplicationListener{
@Override
public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
System.out.println("###############"+"ShasreniuApplicationEnvironmentPreparedEventListener");
SpringApplication springApplication = event.getSpringApplication();
ConfigurableEnvironment environment = event.getEnvironment();
long timestamp = event.getTimestamp();
Object source = event.getSource();
System.out.println("########################"+springApplication);
System.out.println("########################"+environment);
System.out.println("########################"+timestamp);
System.out.println("########################"+source);

MutablePropertySources propertySources = environment.getPropertySources();
if (propertySources!=null) {
Iterator> iterator = propertySources.iterator();
while (iterator.hasNext()) {
PropertySource propertySource = (PropertySource) iterator.next();

System.out.println("##############:propertySource"+propertySource);
}
}
}
}

监听器注册

@RestController
@SpringBootApplication()
public class Application {
@RequestMapping("/")
String index() {
return "xxxxxxxxxxxxx";
}
public static void main(String[] args) {
SpringApplication springApplication = new SpringApplication(Application.class);
springApplication.addListeners(new ShareniuApplicationStartedEventListener());
springApplication.addListeners(new ShasreniuApplicationEnvironmentPreparedEventListener());
springApplication.addListeners(new ShareniuApplicationPreparedEventListener());
springApplication.addListeners(new ShareniuApplicationFailedEventListener());
springApplication.addListeners(new ShareniuApplicationReadyEventListener());
springApplication.addListeners(new ShareniuSpringApplicationEventListener());
springApplication.run(args);
}
}