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