SpringBoot中是如何创建WebServer的？

本文这里环境是springboot 2.2.4.RELEASE。创建WebServer是在refresh方法的onRefresh方法中实现的。其也是refresh方法体系的一个重要步骤。

ServletWebServerApplicationContext的onRefresh方法。如下所示其首先调用父类的onRefresh方法初始化ThemeSource，然后调用createWebServer创建WebServer。

@Override protected void onRefresh() { 
    super.onRefresh(); try { 
    createWebServer(); } catch (Throwable ex) { 
    throw new ApplicationContextException("Unable to start web server", ex); } } //GenericWebApplicationContext @Override protected void onRefresh() { 
    this.themeSource = UiApplicationContextUtils.initThemeSource(this); } 

【1】createWebServer

ServletWebServerApplicationContext的createWebServer方法如下。

private void createWebServer() { 
    WebServer webServer = this.webServer; // 获取的是GenericWebApplicationContext的servletContext  ServletContext servletContext = getServletContext(); if (webServer == null && servletContext == null) { 
    // 本文环境获取的是tomcatServletWebServerFactory 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(); } 

关于initPropertySources();方法可以参考博文：Spring中refresh分析之onRefresh方法详解 。

① 获取WebServerFactory

如下所示，从容器中获取ServletWebServerFactory类型的bean，唯一一个，否则抛出异常。本文环境获取的是tomcatServletWebServerFactory。

protected ServletWebServerFactory getWebServerFactory() { 
    // Use bean names so that we don't consider the hierarchy String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class); if (beanNames.length == 0) { 
    throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing " + "ServletWebServerFactory bean."); } if (beanNames.length > 1) { 
    throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple " + "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames)); } return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class); } 

② getSelfInitializer

ServletWebServerApplicationContext的getSelfInitializer方法，返回的是ServletContextInitializer。

private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() { 
    return this::selfInitialize; } 

看到this::selfInitialize是不是比较迷糊？典型的java8的lambda写法。我们看一下ServletContextInitializer 可能就明白了。

如下所示，其是一个函数式接口，只有一个onStartup方法。函数式接口(有且仅有一个抽象方法的接口)可以使用lambda式的写法。

@FunctionalInterface public interface ServletContextInitializer { 
    // 初始化过程中，使用给定的servlets、filters、listeners //context-params and attributes necessary配置ServletContext void onStartup(ServletContext servletContext) throws ServletException; } 

this指的是AnnotationConfigServletWebServerApplicationContext，其继承于ServletWebServerApplicationContext

private void selfInitialize(ServletContext servletContext) throws ServletException { 
    prepareWebApplicationContext(servletContext); registerApplicationScope(servletContext); WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext); for (ServletContextInitializer beans : getServletContextInitializerBeans()) { 
    beans.onStartup(servletContext); } } 

其实换成匿名类的写法则是：

new ServletContextInitializer() { 
    @Override public void onStartup(ServletContext servletContext) throws ServletException { 
    selfInitialize(servletContext); } }; 

【2】getWebServer

本文这里是TomcatServletWebServerFactory的getWebServer方法。

@Override public WebServer getWebServer(ServletContextInitializer... initializers) { 
    if (this.disableMBeanRegistry) { 
    // registry = new NoDescriptorRegistry(); Registry.disableRegistry(); } //实例化Tomcat Tomcat tomcat = new Tomcat(); //获取临时路径 C:\Users\12746\AppData\Local\Temp\tomcat..8188 File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat"); //设置基础路径 tomcat.setBaseDir(baseDir.getAbsolutePath()); //实例化Connector 并进行配置 Connector connector = new Connector(this.protocol); connector.setThrowOnFailure(true); //这里会实例化server service tomcat.getService().addConnector(connector); customizeConnector(connector); //对Connector做配置比如Protocol、URIEncoding tomcat.setConnector(connector); //这里会实例化Engine、Host tomcat.getHost().setAutoDeploy(false); configureEngine(tomcat.getEngine()); for (Connector additionalConnector : this.additionalTomcatConnectors) { 
    tomcat.getService().addConnector(additionalConnector); } prepareContext(tomcat.getHost(), initializers); return getTomcatWebServer(tomcat); } 

getService

getService首先会触发getServer然后获取service。getServer如下所示会实例化Server并对其进行配置。

public Service getService() { 
    return getServer().findServices()[0]; } public Server getServer() { 
    if (server != null) { 
    return server; } System.setProperty("catalina.useNaming", "false"); // 实例化 server server = new StandardServer(); // 对basedir做处理 initBaseDir(); // Set configuration source ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(new File(basedir), null)); // 为server设置port和service server.setPort( -1 ); //实例化service Service service = new StandardService(); service.setName("Tomcat"); server.addService(service); return server; } 

prepareContext

这里会实例化TomcatEmbeddedContext并对其进行配置。

protected void prepareContext(Host host, ServletContextInitializer[] initializers) { 
    File documentRoot = getValidDocumentRoot(); TomcatEmbeddedContext context = new TomcatEmbeddedContext(); if (documentRoot != null) { 
    context.setResources(new LoaderHidingResourceRoot(context)); } context.setName(getContextPath()); context.setDisplayName(getDisplayName()); context.setPath(getContextPath()); File docBase = (documentRoot != null) ? documentRoot : createTempDir("tomcat-docbase"); context.setDocBase(docBase.getAbsolutePath()); context.addLifecycleListener(new FixContextListener()); context.setParentClassLoader((this.resourceLoader != null) ? this.resourceLoader.getClassLoader() : ClassUtils.getDefaultClassLoader()); resetDefaultLocaleMapping(context); addLocaleMappings(context); context.setUseRelativeRedirects(false); try { 
    context.setCreateUploadTargets(true); } catch (NoSuchMethodError ex) { 
    // Tomcat is < 8.5.39. Continue. } configureTldSkipPatterns(context); WebappLoader loader = new WebappLoader(context.getParentClassLoader()); loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName()); loader.setDelegate(true); context.setLoader(loader); if (isRegisterDefaultServlet()) { 
    addDefaultServlet(context); } if (shouldRegisterJspServlet()) { 
    addJspServlet(context); addJasperInitializer(context); } context.addLifecycleListener(new StaticResourceConfigurer(context)); ServletContextInitializer[] initializersToUse = mergeInitializers(initializers); host.addChild(context); configureContext(context, initializersToUse); postProcessContext(context); } 

getTomcatWebServer

这个方法很简单，只是直接实例化了TomcatWebServer返回。其构造方法触发了initialize，这会引起后续一系列动作，包括tomcat.start。

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) { 
    return new TomcatWebServer(tomcat, getPort() >= 0); } public TomcatWebServer(Tomcat tomcat, boolean autoStart) { 
    Assert.notNull(tomcat, "Tomcat Server must not be null"); this.tomcat = tomcat; this.autoStart = autoStart; initialize(); } 

【3】selfInitialize

获取到TomcatWebServer后，就触发了selfInitialize方法。这里servletContext其实是获取了ApplicationContext的一个门面/外观–ApplicationContextCade。

// ServletWebServerApplicationContext private void selfInitialize(ServletContext servletContext) throws ServletException { 
    prepareWebApplicationContext(servletContext); registerApplicationScope(servletContext); WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext); for (ServletContextInitializer beans : getServletContextInitializerBeans()) { 
    beans.onStartup(servletContext); } } 

① prepareWebApplicationContext

ServletWebServerApplicationContext的prepareWebApplicationContext方法如下所示，简单来讲就是为servletContext设置根容器属性并为当前应用上下文ApplicationContext设置servletContext引用。

protected void prepareWebApplicationContext(ServletContext servletContext) { 
    //尝试从servletContext中获取rootContext  Object rootContext = servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE); if (rootContext != null) { 
    if (rootContext == this) { 
    throw new IllegalStateException( "Cannot initialize context because there is already a root application context present - " + "check whether you have multiple ServletContextInitializers!"); } return; } Log logger = LogFactory.getLog(ContextLoader.class); // 这个日志是不是很熟悉？！ servletContext.log("Initializing Spring embedded WebApplicationContext"); try { 
    //向servletContext设置属性 ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this); if (logger.isDebugEnabled()) { 
    logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" + WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]"); } // 为ApplicationContext设置servletContext引用 setServletContext(servletContext); if (logger.isInfoEnabled()) { 
    long elapsedTime = System.currentTimeMillis() - getStartupDate(); logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms"); } } catch (RuntimeException | Error ex) { 
    logger.error("Context initialization failed", ex); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex); throw ex; } } 

② registerApplicationScope

ServletWebServerApplicationContext的registerApplicationScope方法如下所示，简单来讲就是(扩展)注册scope-application。这里会实例化一个ServletContextScope (包装了servletContext)，然后注册到BeanFactory中并为servletContext设置属性。

private void registerApplicationScope(ServletContext servletContext) { 
    ServletContextScope appScope = new ServletContextScope(servletContext); // application getBeanFactory().registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope); // Register as ServletContext attribute, for ContextCleanupListener to detect it. servletContext.setAttribute(ServletContextScope.class.getName(), appScope); } 

我们在Spring中refresh分析之postProcessBeanFactory方法详解提到了request-RequestScope，session–SessionScope的注册，本文这里注册了application-ServletContextScope注册。

③ registerEnvironmentBeans

WebApplicationContextUtils的registerEnvironmentBeans方法。

public static void registerEnvironmentBeans(ConfigurableListableBeanFactory bf, @Nullable ServletContext sc) { 
    registerEnvironmentBeans(bf, sc, null); } public static void registerEnvironmentBeans(ConfigurableListableBeanFactory bf, @Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) { 
    //将servletContext作为单例注册容器 if (servletContext != null && !bf.containsBean(WebApplicationContext.SERVLET_CONTEXT_BEAN_NAME)) { 
    bf.registerSingleton(WebApplicationContext.SERVLET_CONTEXT_BEAN_NAME, servletContext); } // 将servletConfig 作为单例注册容器本文这里没有触发 if (servletConfig != null && !bf.containsBean(ConfigurableWebApplicationContext.SERVLET_CONFIG_BEAN_NAME)) { 
    bf.registerSingleton(ConfigurableWebApplicationContext.SERVLET_CONFIG_BEAN_NAME, servletConfig); } // String CONTEXT_PARAMETERS_BEAN_NAME = "contextParameters"; if (!bf.containsBean(WebApplicationContext.CONTEXT_PARAMETERS_BEAN_NAME)) { 
    Map<String, String> parameterMap = new HashMap<>(); if (servletContext != null) { 
    // 获取servletContextd的初始化参数 Enumeration<?> paramNameEnum = servletContext.getInitParameterNames(); while (paramNameEnum.hasMoreElements()) { 
    String paramName = (String) paramNameEnum.nextElement(); parameterMap.put(paramName, servletContext.getInitParameter(paramName)); } } // 本文这里servletConfig 为null if (servletConfig != null) { 
    // // 获取servletConfig的初始化参数 Enumeration<?> paramNameEnum = servletConfig.getInitParameterNames(); while (paramNameEnum.hasMoreElements()) { 
    String paramName = (String) paramNameEnum.nextElement(); parameterMap.put(paramName, servletConfig.getInitParameter(paramName)); } } // 将contextParameters作为单例注册到容器 bf.registerSingleton(WebApplicationContext.CONTEXT_PARAMETERS_BEAN_NAME, Collections.unmodifiableMap(parameterMap)); } // String CONTEXT_ATTRIBUTES_BEAN_NAME = "contextAttributes"; if (!bf.containsBean(WebApplicationContext.CONTEXT_ATTRIBUTES_BEAN_NAME)) { 
    Map<String, Object> attributeMap = new HashMap<>(); if (servletContext != null) { 
    Enumeration<?> attrNameEnum = servletContext.getAttributeNames(); while (attrNameEnum.hasMoreElements()) { 
    String attrName = (String) attrNameEnum.nextElement(); attributeMap.put(attrName, servletContext.getAttribute(attrName)); } } // 将contextAttributes作为单例注册到容器 bf.registerSingleton(WebApplicationContext.CONTEXT_ATTRIBUTES_BEAN_NAME, Collections.unmodifiableMap(attributeMap)); } } 

④ 触发ServletContextInitializer的onStartup

如下所示，这里会获取ServletContextInitializer的所有实例，遍历触发其onStartup方法。

for (ServletContextInitializer beans : getServletContextInitializerBeans()) { 
    beans.onStartup(servletContext); }