在上一章中我们介绍了springboot中分析脉络的两个方向,一个是顺着主入口来分析,一个是带着疑问springboot是如何去掉web.xml来分析,本文我们先分析第一个方向
在启动springboot的时候可谓是相当简单,只需要执行以下代码
public static void main(String[] args) {
SpringApplication.run(HppaApplication.class, args);
}
那些看似简单的事物,其实并不简单。我们之所以觉得他简单,是因为复杂性都被隐藏了。通过上诉代码,你大概率可以提出以下几个疑问
SpringApplication.run(HppaApplication.class, args);
这个会最终调用到一个同名方法run(String… args)
public ConfigurableApplicationContext run(String... args) {
//StopWatch主要是用来统计每项任务执行时长,例如Spring Boot启动占用总时长。
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
//第一步:获取并启动监听器 通过加载META-INF/spring.factories 完成了SpringApplicationRunListener实例化工作
SpringApplicationRunListeners listeners = getRunListeners(args);
//实际上是调用了EventPublishingRunListener类的starting()方法
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
//第二步:构造容器环境,简而言之就是加载系统变量,环境变量,配置文件
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
//设置需要忽略的bean
configureIgnoreBeanInfo(environment);
//打印banner
Banner printedBanner = printBanner(environment);
//第三步:创建容器
context = createApplicationContext();
//第四步:实例化SpringBootExceptionReporter.class,用来支持报告关于启动的错误
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//第五步:准备容器 这一步主要是在容器刷新之前的准备动作。包含一个非常关键的操作:将启动类注入容器,为后续开启自动化配置奠定基础。
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
//第六步:刷新容器 springBoot相关的处理工作已经结束,接下的工作就交给了spring。 内部会调用spring的refresh方法,
// refresh方法在spring整个源码体系中举足轻重,是实现 ioc 和 aop的关键。
refreshContext(context);
//第七步:刷新容器后的扩展接口 设计模式中的模板方法,默认为空实现。如果有自定义需求,可以重写该方法。比如打印一些启动结束log,或者一些其它后置处理。
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
//发布应用已经启动的事件
listeners.started(context);
/*
* 遍历所有注册的ApplicationRunner和CommandLineRunner,并执行其run()方法。
* 我们可以实现自己的ApplicationRunner或者CommandLineRunner,来对SpringBoot的启动过程进行扩展。
*/
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
//应用已经启动完成的监听事件
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
很长是吧,这个方法大概做了以下几件事
那么内置tomcat启动源码,就是隐藏在上诉第六步:refreshContext方法里面,该方法最终会调用到AbstractApplicationContext类的refresh()方法
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
onRefresh()会调用到ServletWebServerApplicationContext中的createWebServer()
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
if (webServer == null && servletContext == null) {
ServletWebServerFactory factory = getWebServerFactory();
this.webServer = factory.getWebServer(getSelfInitializer());
}
else if (servletContext != null) {
try {
getSelfInitializer().onStartup(servletContext);
}
catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context", ex);
}
}
initPropertySources();
}
createWebServer()就是启动web服务,但是还没有真正启动Tomcat,既然webServer是通过ServletWebServerFactory来获取的,那就来看看这个工厂的真面目。
可以看到,tomcat,Jetty都实现了这个getWebServer方法,我们看TomcatServletWebServerFactory中的getWebServer(ServletContextInitializer… initializers).
public WebServer getWebServer(ServletContextInitializer... initializers) {
if (this.disableMBeanRegistry) {
Registry.disableRegistry();
}
Tomcat tomcat = new Tomcat();
File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
tomcat.setBaseDir(baseDir.getAbsolutePath());
Connector connector = new Connector(this.protocol);
connector.setThrowOnFailure(true);
tomcat.getService().addConnector(connector);
customizeConnector(connector);
tomcat.setConnector(connector);
tomcat.getHost().setAutoDeploy(false);
configureEngine(tomcat.getEngine());
for (Connector additionalConnector : this.additionalTomcatConnectors) {
tomcat.getService().addConnector(additionalConnector);
}
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}
到此,不知道你有没有看出来内置tomcat是如何启动的,其实就是New了一个Tomcat,你还不知道原来Tomcat还能这样启动啊,确实是可以的,我在没看到源码之前我也不知道还能这样启动。
springboot的内部通过new Tomcat()
的方式启动了一个内置Tomcat。但是这里还有一个问题,这里只是启动了tomcat,但是我们的springmvc是如何加载的呢?下一章我们讲接收,springboot是如何自动装配springmvc的