// 未分类
SpringBoot启动发生了什么。
发布 2019-02-10 · 永久链接
稍微看了下Springboot启动的时候会做些什么
首先是`SpringApplication.run` 方法，方法拿到一个 `primary source` 然后解析加载配置（就是那个传进来的App.class）。
然后创建了个`SpringApplication`,创建的时候会检测这个是什么类型的项目，`this.webApplicationType = WebApplicationType.deduceFromClasspath();`
``` java
public static ConfigurableApplicationContext run(Class[] primarySources,
String[] args) {
return new SpringApplication(primarySources).run(args);
}
```
把参数传进去，然后`run()`,根据项目类型创建`ConfigurableApplicationContext`，
``` java
public ConfigurableApplicationContext run(String... args) {
// 启动计时器
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
// 这个东西用来管理多个listener，在创建的时候，从 META-INF/spring.factories拿到要创建的listener名字，创建实例
SpringApplicationRunListeners listeners = getRunListeners(args);
// 启动listener
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
// 创建运行参数
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
// 输出开头那段Spring boot 什么什么的
Banner printedBanner = printBanner(environment);
// 创建上下文
context = createApplicationContext();
// 异常报告
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//前置上下文配置
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
// 刷新上下文
refreshContext(context);
afterRefresh(context, applicationArguments);
// 计时完毕
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);
}
return context;
}
```
listeners 是拿到这些名字来创建东西的：
``` java
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.ConfigFileApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
```
也就是说，我们是可以自定义Listener然后，监听相应的Event
只要实现`ApplicationListener`
``` java
/**
* @author dqn
* created at 2019/2/10 19:20
*/
public class MyListener implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationEvent event) {
// 监听ApplicationStartingEvent
if (event instanceof ApplicationStartedEvent) {
System.out.println("ApplicationStartedEvent listened");
}
// 监听ApplicationEnvironmentPreparedEvent
else if (event instanceof ApplicationEnvironmentPreparedEvent) {
System.out.println("ApplicationEnvironmentPreparedEvent listened");
}
// 监听ApplicationPreparedEvent
else if (event instanceof ApplicationPreparedEvent) {
System.out.println("ApplicationPreparedEvent listened");
}
// 监听ApplicationReadyEvent
else if (event instanceof ApplicationReadyEvent) {
System.out.println("ApplicationReadyEvent listened");
}
// 监听ApplicationFailedEvent
else if (event instanceof ApplicationFailedEvent) {
System.out.println("ApplicationFailedEvent listened");
}
}
}
```
在`META-INF/spring.factories`加上
```
org.springframework.context.ApplicationListener=\
me.dqn.listener.MyListener
```
即可。当然也可以手动添加：
``` java
public static void main(String[] args) {
SpringApplication application = new SpringApplication(App.class);
application.addListeners(new MyListener());
application.run(args);
}
```