幾個重要的事件回調機制：
1、配置在META-INF/spring.factories
-
ApplicationContextInitializer
-
SpringApplicationRunlistener
2、需要放在ioc容器中
3、ApplicationRunner
4、CommandLineRunner
一、創建SpringApplication對象
快速創建一個工程，在SpringBootApplication類中，main方法作爲一個入口類，在在run（）方法處打上斷點，debug運行；
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
//保存主配置類
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
//判斷當前是否一個web應用
this.webApplicationType = WebApplicationType.deduceFromClasspath();
//從類路徑系找到META-INF/spring.factories配置的所有ApplicationContextInitializer，然後保存起來
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
//從類路徑系找到META-INF/spring.factories配置的所有ApplicationListener
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
//從多個配置類中找到有main方法的主配置類
this.mainApplicationClass = deduceMainApplicationClass();
}
二、運行run方法
接着上一步的繼續進行：
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
//獲取SpringApplicationRunListeners ，從類路徑下METTA-INF/spring.factories
SpringApplicationRunListeners listeners = getRunListeners(args);
//回調所有的SpringApplicationRunListeners.starting方法
listeners.starting();
try {
//封裝命令行參數
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
//準備環境
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
//創建環境完成後回調SpringApplicationRunListeners.environmentPrepared();表示環境準備完成
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
//創建applicationContext，決定創建web的ioc還是普通的ioc
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//準備上下文環境；將environment保存到ioc中；而且applyInitializers（）
//applyInitializers()：回調之前保存的所有的ApplicationContextInitializer的Initialize方法
//回調所有的SpringApplicationRunListeners.contextPrepared（）
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
//prepareContext運行完成以後回調所有的SpringApplicationRunListeners的contextLoaded（）
//刷新容器；ioc容器初始化（如果是web應用還會創建嵌入式的tomcat）；spring註解
//掃描，創建，加載所有組件的地方；（配置類，組件，自動配置）
refreshContext(context);
//從ioc容器中獲取所有的ApplicationRunner和CommandLineRunner進行回調
//ApplicationRunner先回調，CommandLineRunner再回調
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);
}
//整個SpringBoot應用啓動完成以後返回啓動的ioc容器
return context;
}
三、事件監聽機制
依次將上面的幾個監聽機制進行創建，
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是需要進行配置的，配置的位置是在META-INF/spring.factories中，因此創建一個META-INF的文件夾，並創建spring.factories文件，
然後在spring.factories文件中進行配置：
org.springframework.context.ApplicationContextInitializer=\
com.itlaoqi.springbootspringbootapplication.listener.HelloApplicationContextInitializer
org.springframework.context.SpringApplicationRunListener=\
com.itlaoqi.springbootspringbootapplication.listener.HelloSpringApplicationRunListener
配置完成後啓動項目即可進行測試。