Spring Boot 2.x：SpringBoot

几个重要的事件回调机制：

1、配置在META-INF/spring.factories

ApplicationContextInitializer

SpringApplicationRunlistener

2、需要放在ioc容器中

3、ApplicationRunner

4、CommandLineRunner

一、创建SpringApplication对象

快速创建一个工程，在SpringBootApplication类中，main方法作为一个入口类，在在run（）方法处打上断点，debug运行；

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {

//保存主配置类

this.resourceLoader = resourceLoader;

Assert.notNull(primarySources, "PrimarySources must not be null");

this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));

//判断当前是否一个web应用

this.webApplicationType = WebApplicationType.deduceFromClasspath();

//从类路径系找到META-INF/spring.factories配置的所有ApplicationContextInitializer，然后保存起来

setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));

//从类路径系找到META-INF/spring.factories配置的所有ApplicationListener

setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));

//从多个配置类中找到有main方法的主配置类

this.mainApplicationClass = deduceMainApplicationClass();

}

二、运行run方法

接着上一步的继续进行：

public ConfigurableApplicationContext run(String... args) {

StopWatch stopWatch = new StopWatch();

stopWatch.start();

ConfigurableApplicationContext context = null;

Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();

configureHeadlessProperty();

//获取SpringApplicationRunListeners ，从类路径下METTA-INF/spring.factories

SpringApplicationRunListeners listeners = getRunListeners(args);

//回调所有的SpringApplicationRunListeners.starting方法

listeners.starting();

try {

//封装命令行参数

ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);

//准备环境

ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);

//创建环境完成后回调SpringApplicationRunListeners.environmentPrepared();表示环境准备完成

configureIgnoreBeanInfo(environment);

Banner printedBanner = printBanner(environment);

//创建applicationContext，决定创建web的ioc还是普通的ioc

context = createApplicationContext();

exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,

new Class[] { ConfigurableApplicationContext.class }, context);

//准备上下文环境；将environment保存到ioc中；而且applyInitializers（）

//applyInitializers()：回调之前保存的所有的ApplicationContextInitializer的Initialize方法

//回调所有的SpringApplicationRunListeners.contextPrepared（）

prepareContext(context, environment, listeners, applicationArguments, printedBanner);

//prepareContext运行完成以后回调所有的SpringApplicationRunListeners的contextLoaded（）

//刷新容器；ioc容器初始化（如果是web应用还会创建嵌入式的tomcat）；spring注解

//扫描，创建，加载所有组件的地方；（配置类，组件，自动配置）

refreshContext(context);

//从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调

//ApplicationRunner先回调，CommandLineRunner再回调

afterRefresh(context, applicationArguments);

stopWatch.stop();

if (this.logStartupInfo) {

new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);

}

listeners.started(context);

callRunners(context, applicationArguments);

}

catch (Throwable ex) {

handleRunFailure(context, ex, exceptionReporters, listeners);

throw new IllegalStateException(ex);

}

try {

listeners.running(context);

}

catch (Throwable ex) {

handleRunFailure(context, ex, exceptionReporters, null);

throw new IllegalStateException(ex);

}

//整个SpringBoot应用启动完成外汇返佣以后返回启动的ioc容器

return context;

}三、事件监听机制

依次将上面的几个监听机制进行创建，

HelloApplicationContextInitializer：

public class HelloApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

@Override

public void initialize(ConfigurableApplicationContext applicationContext) {

System.out.println("ApplicationContextInitializer...initialize..." + applicationContext);

}

}

HelloSpringApplicationRunListener：

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {

public HelloSpringApplicationRunListener(SpringApplication application, String[] args){

}

@Override

public void starting() {

System.out.println("SpringApplicationRunListener...starting...");

}

@Override

public void environmentPrepared(ConfigurableEnvironment environment) {

Object o = environment.getSystemProperties().get("os.name");

System.out.println("SpringApplicationRunListener...environment" +o);

}

@Override

public void contextPrepared(ConfigurableApplicationContext context) {

System.out.println("SpringApplicationRunListener...contextPrepared");

}

@Override

public void contextLoaded(ConfigurableApplicationContext context) {

System.out.println("SpringApplicationRunListener...contextLoaded");

}

@Override

public void started(ConfigurableApplicationContext context) {

System.out.println("SpringApplicationRunListener...started");

}

@Override

public void running(ConfigurableApplicationContext context) {

System.out.println("SpringApplicationRunListener...running");

}

@Override

public void failed(ConfigurableApplicationContext context, Throwable exception) {

System.out.println("SpringApplicationRunListener...failed");

}

}

HelloApplicationRunner：

@Component

public class HelloAppicationRunner implements ApplicationRunner {

@Override

public void run(ApplicationArguments args) throws Exception {

System.out.println("ApplicationRunner...run..");

}

}

HelloCommandLineRuinner：

@Component

public class HelloCommandLineRunner implements CommandLineRunner{

@Override

public void run(String... args) throws Exception {

System.out.println("CommandLineRunner...run..." + Arrays.asList());

}

}

前面提到的ApplicationContextInitializer和SpringApplicationRunlistener是需要进行配置的，配置的位置是在META-INF/spring.factories中，因此创建一个META-INF的文件夹，并创建spring.factories文件，

org.springframework.context.ApplicationContextInitializer=\

com.itlaoqi.springbootspringbootapplication.listener.HelloApplicationContextInitializer

org.springframework.context.SpringApplicationRunListener=\

com.itlaoqi.springbootspringbootapplication.listener.HelloSpringApplicationRunListener

配置完成后启动项目即可进行测试。

原文链接：https://blog.csdn.net/cyl101816/article/details/103582373