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
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();
}
//new了一个Tomcat
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);
}
很关键的依据代码Tomcat tomcat = new Tomcat();
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
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原创声明:本文系作者授权腾讯云开发者社区发表,未经许可,不得转载。
如有侵权,请联系 cloudcommunity@tencent.com 删除。