springboot启动一个项目代码例子如下
SpringApplication.run(xxxx.class, args);
跟踪进去如下
public static ConfigurableApplicationContext run(Class<?> primarySource,
String... args) {
return run(new Class<?>[] { primarySource }, args);
}
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
return new SpringApplication(primarySources).run(args);
}
上面是创建了一个SpringApplication对象，然后调用其run方法
SpringApplication构造方法：
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
//上面传null
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
//上面传运行的主方法的类
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
//三种类型：REACTIVE|NONE|SERVLET；REACTIVE对应spring5新增的webflux；SERVLET是传统servlet
this.webApplicationType = deduceWebApplicationType();
//从META-INF/spring.factories文件获取ApplicationContextInitializer类型的类
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
//从META-INF/spring.factories文件获取ApplicationListener类型的类
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
//获取运行的主方法的类
this.mainApplicationClass = deduceMainApplicationClass();
}
创建了SpringApplication对象后，接着执行它的run方法
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();//性能监控
//Spring容器类
ConfigurableApplicationContext context = null;
//SpringBootExceptionReporter类
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();//设置系统的“java.awt.headless”属性
//从META-INF/spring.factories中获得SpringApplicationRunListener类型的类，放进SpringApplicationRunListeners
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();//开始事件
try {
//命令行启动的参数封装到DefaultApplicationArguments
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//【标记1】实例或配置好environment
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
//对系统中的“spring.beaninfo.ignore”属性进行处理
configureIgnoreBeanInfo(environment);
//打印招牌
Banner printedBanner = printBanner(environment);
//【标记2】创建容器，三种类型
context = createApplicationContext();
//从META-INF/spring.factories中获取SpringBootExceptionReporter类型的类
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//【标记3】准备容器
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
//刷新容器
refreshContext(context);
//留给子类实现
afterRefresh(context, applicationArguments);
//性能监控停止
stopWatch.stop();
//打印信息，主要关于启动时间
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
//监听器回调started
listeners.started(context);
//执行ApplicationRunner、CommandLineRunner（还没看懂怎么启动的）
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
//会回调listener的failed方法
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
//监听器回调running方法
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
上面的springboot的启动流程一目了然了，准备好环境environment，准备好容器context，然后加载好各种资源到容器中，接着启动。
【标记1】实例或配置好environment
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// 创建Environment类型对象，三种：StandardServletEnvironment|StandardReactiveWebEnvironment|StandardEnvironment
ConfigurableEnvironment environment = getOrCreateEnvironment();
//配置Environment的一些属性
configureEnvironment(environment, applicationArguments.getSourceArgs());
//监听器回调environmentPrepared方法
listeners.environmentPrepared(environment);
//绑定environment（其实还没看懂干嘛）
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
//这里再次检测是否需要把environment转为对应类型的environment，上面getOrCreateEnvironment里不是判断过了吗？？
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
//这里把environment中的propertySources成员中的configurationProperties键对应的值替换为SpringConfigurationPropertySources
ConfigurationPropertySources.attach(environment);
return environment;
}
【标记2】创建容器，三种类型
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
case SERVLET:
contextClass = Class.forName(DEFAULT_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch...
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
【标记3】准备容器
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
//设置environment
context.setEnvironment(environment);
//设置bean名字生成器、resourceloader、classloader、ApplicationConversionService
postProcessApplicationContext(context);
//执行从META-INF/spring.factories中获取的ApplicationContextInitializer类型的initialize方法
applyInitializers(context);
//监听器回调contextPrepared方法，容器已经准备好
listeners.contextPrepared(context);
//打印信息：主要关于active profile的
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
//向beanFactory注册了bean
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
if (beanFactory instanceof DefaultListableBeanFactory) {
//设置是否允许覆盖bean
((DefaultListableBeanFactory) beanFactory)
.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
// Load the sources
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
//开始加载资源
load(context, sources.toArray(new Object[0]));
//监听器回调contextLoaded，容器已经加载完
listeners.contextLoaded(context);
}
prepareContext方法中会执行ApplicationContextInitializer的initialize方法，执行完的时候，当prepareContext方法执行完容器已加载好了资源
总结一下SpringApplicationRunListener的回调顺序
SpringApplicationRunListener共7个方法，回调顺序为：
starting -> environmentPrepared -> contextPrepared -> contextLoaded -> started -> running
failed方法在running前执行有错误发现才回调