[Java知识库]SpringBoot事件机制

SpringBoot事件机制

启动入口

SpringApplication.run(H2Application.class, args);方法

public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		DefaultBootstrapContext bootstrapContext = createBootstrapContext();
		ConfigurableApplicationContext context = null;
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
    	//1.发送ApplicationStartingEvent事件，回调starting
		listeners.starting(bootstrapContext, this.mainApplicationClass);
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //2.发送ApplicationEnvironmentPreparedEvent事件，回调environmentPrepared,
            //listeners.environmentPrepared(bootstrapContext, environment);
			ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			context.setApplicationStartup(this.applicationStartup);
            //3.listeners.contextPrepared(context);
            //4.listeners.contextLoaded(context);
			prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
            //5.ApplicationStartedEvent事件 listeners.started(context);
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
            //ApplicationFailedEvent
			handleRunFailure(context, ex, listeners);
			throw new IllegalStateException(ex);
		}

		try {
            //6.ApplicationReadyEvent事件 listeners.running(context);
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

事件整理

事件含义：

自定义事件

复用SpringBoot内置事件机制，自定义，参考：context.publishEvent(new ExitCodeEvent(context, exitCode));

这里顺便梳理一下SprinBoot的启动流程，我们知道SpringBoot的启动入口是SpringApplication#run，涉及SpringApplication的构造函数和run方法。

• SpringApplication的构造函数

  1. 将启动类放入primarySource；this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));

  2. 推算当前web应用类型；this.webApplicationType = WebApplicationType.deduceFromClasspath();

  3. 读取ApplicationContextInitializer初始化器，ApplicationListener配置并赋值

     getSpringFactoriesInstances(ApplicationContextInitializer.class)//this.initializers
     getSpringFactoriesInstances(ApplicationListener.class))//this.listeners
     

  4. 将main方法所有的类放入mainApplicationClass; this.mainApplicationClass = deduceMainApplicationClass();

• run方法

  1. 记录启动时间，开启hendless,读取SpringApplicationRunListener配置；发布ApplicationStartingEvent

  2. 封装命令行参数applicationArgument，读取环境配置prepareEnvironment，在其中发布ApplicationEnvironmentPreparedEvent

  3. 设置忽略的bean，configureIgnoreBeanInfo，从系统变量中获取"spring.beaninfo.ignore"并设置

  4. 打印banner

  5. 创建applicationContext

  6. 准备applicationContext，在其中发布ApplicationContextInitializedEvent

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  7. 刷新applicationContext

  8. 刷新后applicationContext，留待扩展，完成后发布ApplicationStartedEvent，执行完Runners后，发布ApplicationReadyEvent

定阅事件

@Component
public class UserRegisterSendSMSListener implements ApplicationListener<UserRegisterEvent> {
 
    private static final Logger LOGGER = LoggerFactory.getLogger(UserRegisterSendSMSListener.class);
 
    @Override
    public void onApplicationEvent(UserRegisterEvent userRegisterEvent) {
        // 发送短信
        LOGGER.info("新注册用户 {} 短信发送成功", userRegisterEvent.getUser().getUserName());
    }
}

发布事件

@RestController
@RequestMapping("user")
public class UserController {
 
    @Autowired
    private ApplicationEventPublisher applicationEventPublisher;
 
    @PostMapping
    public String register(@RequestBody UserModel model) {
        // 验证
        // 注册
        // 事件
        UserRegisterEvent userRegisterEvent = new UserRegisterEvent(this, model);
        applicationEventPublisher.publishEvent(userRegisterEvent);
        return Boolean.TRUE.toString();
    }
}

自定义监听

package com.dxz.controller;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;

public class SampleSpringApplicationRunListener implements SpringApplicationRunListener {
    private final SpringApplication application;
    private final String[] args;
	
    //任何一个SpringApplicationRunListener实现类的构造方法都需要有两个构造参数，一个参数的类型就是我们的org.springframework.boot.SpringApplication,另外一个参数就是args参数列表的String[]
    public SampleSpringApplicationRunListener(SpringApplication sa, String[] args) {
        this.application = sa;
        this.args = args;
    }

    @Override
    public void starting() {
        System.out.println("自定义starting");
    }

    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        System.out.println("自定义environmentPrepared");
    }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("自定义contextPrepared");
    }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("自定义contextLoaded");
    }

    @Override
    public void finished(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("自定义finished");
    }
}

org.springframework.boot.SpringApplicationRunListener=\
    com.dxz.SampleSpringApplicationRunListener