spring boot實戰(第二篇)事件監聽

前言

spring boot在啓動過程中增加事件監聽機制，爲用戶功能拓展提供極大的便利。

支持的事件類型四種

ApplicationStartedEvent
ApplicationEnvironmentPreparedEvent
ApplicationPreparedEvent
ApplicationFailedEvent

實現監聽步驟：

1.監聽類實現ApplicationListener接口
2.將監聽類添加到SpringApplication實例

ApplicationStartedEvent

ApplicationStartedEvent：spring boot啓動開始時執行的事件

創建對應的監聽類 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 啓動監聽類
 * 
 * @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);// 不顯示banner信息
        logger.info("==MyApplicationStartedEventListener==");
    }
}

在該事件中可以獲取到SpringApplication對象，可做一些執行前的設置.

Application.java類

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 對應Enviroment已經準備完畢，但此時上下文context還沒有創建。

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 配置環境事件監聽
 * @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<ApplicationEnvironmentPreparedEvent> {
    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<PropertySource<?>> iter = mps.iterator();
            while (iter.hasNext()) {
                PropertySource<?> ps = iter.next();
                logger
                    .info("ps.getName:{};ps.getSource:{};ps.getClass:{}", ps.getName(), ps.getSource(), ps.getClass());
            }
        }
    }

}

在該監聽中獲取到ConfigurableEnvironment後可以對配置信息做操作，例如：修改默認的配置信息，增加額外的配置信息等等~~~

ApplicationPreparedEvent

ApplicationPreparedEvent:spring boot上下文context創建完成，但此時spring中的bean是沒有完全加載完成的。

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;

/**
 * 上下文創建完成後執行的事件監聽器
 * 
 * @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);
    }

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

}

在獲取完上下文後，可以將上下文傳遞出去做一些額外的操作。

在該監聽器中是無法獲取自定義bean並進行操作的。

ApplicationFailedEvent

ApplicationFailedEvent:spring boot啓動異常時執行事件
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);
    }

    /*處理異常*/
    private void handleThrowable(Throwable throwable) {
    }

}

在異常發生時，最好是添加虛擬機對應的鉤子進行資源的回收與釋放，能友善的處理異常信息。

在spring boot中已經爲大家考慮了這一點，默認情況開啓了對應的功能：

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()方法中進行資源的回收與釋放。

結束語

spring boot提供的四種監聽事件到這裏就結束了，針對實際業務可添加自定義的監聽器，下一節當中將會對spring boot中的監聽源碼進行分析，理解爲什麼是這樣的。

spring boot監聽器使用

分享牛 2017-04-18 4124℃

摘要：spring boot提供了一系列的監聽器，方便我們開發人員使用和擴展。

本文咱們詳細講解一下spring boot中的監聽器。

spring boot中支持的事件類型定在org.springframework.boot.context.event包中，目前支持的事件類型有如下6種：

ApplicationFailedEvent
ApplicationPreparedEvent
ApplicationReadyEvent
ApplicationStartedEvent
SpringApplicationEvent
ApplicationEnvironmentPreparedEvent

監聽器的使用

第一：首先定義一個自己使用的監聽器類並實現ApplicationListener接口。

第二：通過SpringApplication類中的addListeners方法將自定義的監聽器註冊進去。

ApplicationFailedEvent

ApplicationFailedEvent：該事件爲spring boot啓動失敗時的操作

/**
* spring boot 啓動的時候出現異常事件
* @author www.shareniu.com
*
*/
public class ShareniuApplicationFailedEventListener implements ApplicationListener<ApplicationFailedEvent> {
@Override
public void onApplicationEvent(ApplicationFailedEvent event) {
System.out.println("--------------:ShareniuApplicationFailedEventListener");
Throwable exception = event.getException();
System.out.println(exception);
}
}

可以通過ApplicationFailedEvent 獲取Throwable實例對象獲取異常信息並處理。

ApplicationPreparedEvent

ApplicationPreparedEvent：上下文準備事件。

上下文context已經準備完畢，可以通過ApplicationPreparedEvent獲取到ConfigurableApplicationContext實例對象。ConfigurableApplicationContext類繼承ApplicationContext類，但需要注意這個時候spring容器中的bean還沒有被完全的加載，因此如果通過ConfigurableApplicationContext獲取bean會報錯的。比如報錯：

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

獲取到上下文之後，可以將其注入到其他類中，畢竟ConfigurableApplicationContext爲引用類型

public class ShareniuApplicationPreparedEventListener implements ApplicationListener<ApplicationPreparedEvent> {
@Override
public void onApplicationEvent(ApplicationPreparedEvent event) {
System.out.println("###############"+"ShareniuApplicationPreparedEventListener");
ConfigurableApplicationContext applicationContext = event.getApplicationContext();
//如果執行下面代碼則報錯
//ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);
//System.out.println(shareniuDemo);
}
}

ApplicationReadyEvent

ApplicationReadyEvent：上下文已經準備ok。

這個時候就可以通過ApplicationReadyEvent獲取ConfigurableApplicationContext，然後通過ConfigurableApplicationContext 獲取bean的信息。

public class ShareniuApplicationReadyEventListener implements ApplicationListener<ApplicationReadyEvent> {
@Override
public void onApplicationEvent(ApplicationReadyEvent event) {
System.out.println("--------------------:ShareniuApplicationReadyEventListener");
ConfigurableApplicationContext applicationContext = event.getApplicationContext();
//ShareniuDemo可以根基自身情況進行測試
ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);
}
}

ApplicationStartedEvent

ApplicationStartedEvent：spring boot 啓動監聽類。

可以在SpringApplication啓動之前做一些手腳，比如修改SpringApplication實例對象中的屬性值

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

SpringApplicationEvent

SpringApplicationEvent：獲取SpringApplication

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

ApplicationEnvironmentPreparedEvent

ApplicationEnvironmentPreparedEvent：環境事先準備，spring boot中的環境已經準備ok

可以通過ApplicationEnvironmentPreparedEvent獲取到SpringApplication、ConfigurableEnvironment等等信息，可以通過ConfigurableEnvironment實例對象來修改以及獲取默認的環境信息。

public class ShasreniuApplicationEnvironmentPreparedEventListener  implements ApplicationListener<ApplicationEnvironmentPreparedEvent>{
@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<PropertySource<?>> iterator = propertySources.iterator();
while (iterator.hasNext()) {
PropertySource<?> propertySource = (PropertySource<?>) iterator.next();

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

監聽器註冊

@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);
}
}

spring boot實戰(第二篇)事件監聽

spring boot實戰(第二篇)事件監聽

前言

支持的事件類型四種

實現監聽步驟：

ApplicationStartedEvent

ApplicationEnvironmentPreparedEvent

ApplicationPreparedEvent

ApplicationFailedEvent

結束語

spring boot監聽器使用

監聽器的使用

ApplicationFailedEvent

ApplicationPreparedEvent

ApplicationReadyEvent

ApplicationStartedEvent

SpringApplicationEvent

ApplicationEnvironmentPreparedEvent

監聽器註冊

測試人員都是畫畫大神，讓我看看誰還不會用代碼圖？

Object.values()對象遍歷

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【java虛擬機】java虛擬機的類加載機制

【SpringMVC學習11】SpringMVC中的攔截器

如何寫出正確的單例模式

【SpringMVC學習04】Spring、MyBatis和SpringMVC的整合

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