Die in diesem Artikel verwendete Spring-Version ist Spring6, die SpringBoot-Version ist 3 und das JDK ist 17. Es unterscheidet sich möglicherweise geringfügig von zuvor, aber der Gesamtprozess unterscheidet sich nicht allzu sehr.
Wenn die bereitgestellte Anwendung im Tomcat-Webapps-Verzeichnis gestartet wird, müssen Sie das Web konfigurieren. Sie können das context-param-Tag verwenden, um Initialisierungsparameter festzulegen. Diese Parameter sind in der gesamten Webanwendung verfügbar und können über die Methode getInitParameter() des ServletContext-Objekts abgerufen werden.
ContextLoaderListener implementiert die ServletContextListener-Schnittstelle. Diese Schnittstelle wird von Tomcat für die Initialisierung der Kontextumgebung verwendet. Sie wird zum Laden des ApplicationContext verwendet, wenn die Webanwendung gestartet wird.
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/spring/application-context.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>ContextLoaderListener erbt auch die ContextLoader-Klasse und alle Kontextoperationen werden in dieser Klasse ausgeführt.
// 在所有的servlet和filter初始化之前被调用
default public void contextInitialized(ServletContextEvent sce) {
}
// 在所有的servlet和filter销毁之后被调用
default public void contextDestroyed(ServletContextEvent sce) {
}Spring-Kontext initialisieren.
InitWebApplicationContext-Methodenschlüsselcode
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}ApplicationContext erstellen
In der Methode „createWebApplicationContext“ rufen Sie zunächst die Methode „defineContextClass“ auf, um zu bestimmen, welcher ApplicationContext verwendet werden soll.
...
if (this.context == null) {
// 创建ApplicationContext
this.context = createWebApplicationContext(servletContext);
}
...
// 刷新ApplicationContext
configureAndRefreshWebApplicationContext(cwac, servletContext);
...
// 将当前ApplicationContext添加到ServletContext的属性中，后面有用再说
// String ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE = WebApplicationContext.class.getName() + ".ROOT";
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
...Die Konfiguration in web.xml lautet wie folgt:
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
Diese Klasse ist in der Datei ContextLoader.properties unter demselben Pfadpaket wie ContextLoader definiert.
<context-param>
<param-name>contextClass</param-name>
<param-value>com.xxx.XxxContext</param-value>
</context-param>ApplicationContext konfigurieren und aktualisieren
configureAndRefreshWebApplicationContext-Schlüsselcode
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext
Zu diesem Zeitpunkt hat Tomcat die Spring-Umgebung gestartet, und die Folge ist der Spring-Initialisierungsprozess, der hier nicht beschrieben wird.
DispatcherServlet initialisieren
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac,ServletContext sc) {
// ...
// 获取web.xml中配置的contextConfigLocation参数
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}
// ...
// 刷新上下文
wac.refresh();
}<servlet>
<servlet-name>dispatcher</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/spring/dispatcher-servlet.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>DispatcherServlet-Klassendiagramm
Sie können sehen Das DispatcherServlet implementiert die Servlet-Schnittstelle. In der Servlet-Schnittstelle gibt es eine Init-Methode, und die SpringMVC-Konfiguration wird während der Initialisierung geladen. Die Schlüsselcodes befinden sich in den Methoden HttpServletBean.init() und FrameworkServlet.initServletBean(). HttpServletBean.init()<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-4.3.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd">
<!-- 扫描控制器和其他组件 -->
<context:component-scan base-package="com.example.controller" />
<!-- 配置视图解析器 -->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/views/" />
<property name="suffix" value=".jsp" />
</bean>
<!-- 启用Spring MVC注解支持 -->
<mvc:annotation-driven />
</beans>
FrameworkServlet.initServletBean()public final void init() throws ServletException {
// Set bean properties from init parameters.
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
// Let subclasses do whatever initialization they like.
initServletBean();
}FrameworkServlet.initWebApplicationContext()
protected final void initServletBean() throws ServletException {
...
// 在这里初始化ApplicationContext
this.webApplicationContext = initWebApplicationContext();
// 初始化servlet
initFrameworkServlet();
}protected WebApplicationContext initWebApplicationContext() {
// 此处获取根容器，就是Spring初始化的XmlWebApplicationContext，
// 在上面把它添加到了ServletContext的属性中，标记根容器，这里把它获取出来
// String ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE = WebApplicationContext.class.getName() + ".ROOT";
// servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
// 此时webApplicationContext还是null，因为DispatchServlet是被tomcat创建的，需要无参构造器
// 构造器中没有设置webApplicationContext的代码，所以此时webApplicationContext还是null
// 注意：在SpringBoot使用嵌入式Tomcat时，这个webApplicationContext不为null，因为FrameworkServlet还
// 实现了ApplicationContextAware接口，所以当SpringBoot的上下文准备好之后，会回调setApplicationContext方法
// 注入ApplicationContext，后面在细说
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext cwac && !cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
// 此处主要是获取web.xml配置的WebApplicationContext
// 可以通过设置参数contextAttribute来设置加载SpringMVC的ApplicationContext
// 比如下面这样。除非项目中有多个WebApplicationContext，需要使用其他WebApplicationContext才会用到
// 一般都是null
// <context-param>
// <param-name>contextAttribute</param-name>
// <param-value>myWebApplicationContext</param-value>
// </context-param>
wac = findWebApplicationContext();
}
if (wac == null) {
// 现在进入到创建SpringMVC的ApplicationContext流程
// 也就是加载contextConfigLocation定义的xml文件
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
synchronized (this.onRefreshMonitor) {
// 初始化策略对象
// 比如：HandlerMapping，HandlerAdapter，ViewResolver等等
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}DispatchServlet-Initialisierung abgeschlossen
Warum brauchen wir einen Eltern-Kind-Container?In der dreistufigen J2EE-Architektur verwenden wir im Allgemeinen das Spring-Framework in der Serviceschicht, während es in der Webschicht viele Auswahlmöglichkeiten gibt, wie z. B. Spring MVC, Struts usw. Damit die Webschicht die Beans der Serviceschicht verwenden kann, müssen wir den Serviceschichtcontainer als übergeordneten Container des Webschichtcontainers verwenden, damit die Framework-Integration erreicht werden kann.
Die Rolle des Eltern-Kind-Containers besteht darin, dass wir, wenn wir versuchen, eine Bean aus dem untergeordneten Container (Servlet WebApplicationContext) abzurufen, sie, wenn sie nicht gefunden wird, zur Suche an den übergeordneten Container (Root WebApplicationContext) delegieren Es. Die wiederholte Definition derselben Beans in jedem Untercontainer wird vermieden, wodurch die Wiederverwendbarkeit und Wartbarkeit des Codes verbessert wird.
Empfangen Sie die Anfrage
doDispatch-Schlüsselcode
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
// SpringMVC所使用的contextClass，可以在<servlet>标签下设置
// <init-param>
// <param-name>contextClass</param-name>
// <param-value>org.springframework.web.context.support.XmlWebApplicationContext</param-value>
// </init-param>
// 默认为XmlWebApplicationContext
Class<?> contextClass = getContextClass();
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
// 实例化ApplicationContext
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
// 设置环境参数
wac.setEnvironment(getEnvironment());
// 设置父容器为Spring的ApplicationContext
wac.setParent(parent);
// 获取SpringMVC的contextConfigLocation文件
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
// 配置并刷新ApplicationContext
configureAndRefreshWebApplicationContext(wac);
return wac;
}HandlerExecutionChain ist die Handler-Ausführungskette, die das Handler-Objekt und eine Reihe von HandlerInterceptor umschließt. HandlerInterceptor ist ein Interceptor, der vor und nach der Ausführung des Handlers einige zusätzliche Vorgänge ausführen kann, z. B. Berechtigungsprüfung, Protokollierung usw.
HandlerAdapter ist der Handler-Adapter. Er kann verschiedene Arten von Handler-Objekten verarbeiten, die entsprechenden Methoden aufrufen und ModelAndView-Objekte zurückgeben. HandlerAdapter kann je nach Typ des Handlerobjekts Parameterbindung, Rückgabewertverarbeitung und andere Vorgänge durchführen.
在preHandle方法中，可以获取请求和响应对象，进行预处理，比如检查请求头中的token，或者判断请求的url是否有权限访问等。如果返回true，则继续执行后续的拦截器或者处理器；如果返回false，则中断请求，不再执行后续的拦截器或者处理器。
在postHandle方法中，可以获取请求和响应对象，以及处理器返回的ModelAndView对象，进行后处理，比如修改模型数据或者视图信息等。只有在preHandle方法返回true并且处理器成功执行后，该方法才会被调用。
在afterCompletion方法中，可以获取请求和响应对象，以及处理器抛出的异常对象（如果有的话），进行清理资源或者异常处理等。只有当preHandle方法返回true时，无论处理器是否成功执行，该方法才会被调用。
在SpringMVC配置文件中，需注册拦截器类并指定拦截的URL模式。可以注册多个拦截器，并指定顺序。拦截器会按照顺序执行preHandle方法，然后按照逆序执行postHandle和afterCompletion方法。
HandlerInterceptor和Filter的区别
HandlerInterceptor利用Java反射机制实现，而Filter则通过函数回调方式实现。HandlerInterceptor可以利用Spring的AOP技术，实现更灵活的拦截逻辑，而Filter只能在请求前后进行简单的处理。
HandlerInterceptor不依赖于Servlet容器，而Filter依赖于Servlet容器。HandlerInterceptor是SpringMVC框架提供的，可以在任何情况下使用，而Filter是Servlet规范的一部分，只能在Web应用中使用。
HandlerInterceptor的执行由SpringMVC框架控制，而Filter的执行由Servlet容器控制。HandlerInterceptor可以通过IoC容器来管理，可以注入其他的Bean，而Filter则需要在web.xml中配置，或者使用@WebFilter注解，并且需要@ServletComponentScan扫描。
HandlerInterceptor只能拦截DispatcherServlet处理的请求，而Filter可以拦截任何请求。HandlerInterceptor只能对Controller方法进行拦截，而Filter可以对静态资源、JSP页面等进行拦截。
HandlerInterceptor有三个方法：preHandle，postHandle和afterCompletion，分别在请求处理前后和视图渲染前后执行，而Filter只有一个方法：doFilter，在请求处理前后执行。
对于被controller方法，使用的适配器是RequestMappingHandlerAdapter，在handlerAdapter.handle方法执行时，会去执行对应的controller方法，处理controller方法返回的结果。
invocableMethod.invokeAndHandle(webRequest, mavContainer);
ServletInvocableHandlerMethod.invokeAndHandle
// 执行controller方法
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
...
// 处理返回数据，会判断是不是有@ResponseBody注解，如果有，会使用RequestResponseBodyMethodProcessor来处理返回值
// 然后会解析请求头等等，判断应该返回什么类型的数据，然后使用对应的HttpMessageConverter写入输出流
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);SpringBoot使用嵌入式Servlet容器启动应用，有Tomcat，Jetty，Undertow。
SpringBoot默认使用Tomcat，可以在配置文件中看出。
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>web模块自动引入了tomcat
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-tomcat</artifactId> </dependency>
如果不使用Tomcat可以排除，引入其他服务器。
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<!-- 剔除Tomcat -->
<exclusions>
<exclusion>
<artifactId>spring-boot-starter-tomcat</artifactId>
<groupId>org.springframework.boot</groupId>
</exclusion>
</exclusions>
</dependency>
<!-- 使用jetty -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jetty</artifactId>
</dependency>如果没有排除Tomcat，直接引入其他服务器，比如下面。
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <!-- 没有排除Tomcat --> </dependency> <!-- 引入jetty --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jetty</artifactId> </dependency>
如果项目中同时引入了Tomcat和其他服务器的依赖，那么SpringBoot会按照以下顺序来选择启动的服务器。
Tomcat > Jetty > Undertow
也就是说，如果有Tomcat，就优先使用Tomcat，如果没有Tomcat，就看有没有Jetty，如果有Jetty，就使用Jetty，以此类推。这个顺序是在SpringBoot的ServletWebServerFactoryConfiguration类中定义的。
// 只展示必要代码
class ServletWebServerFactoryConfiguration {
// 当Servlet、Tomcat、UpgradeProtocol类在类路径存在时
// 并且ServletWebServerFactory类存在，则会创建tomcatServletWebServerFactory bean。
@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedTomcat {
@Bean
TomcatServletWebServerFactory tomcatServletWebServerFactory(
... 代码省略
}
}
// 当Servlet、Server、WebAppContext类在类路径存在时
// 并且ServletWebServerFactory类型的Bean不存在时，则会创建JettyServletWebServerFactory bean。
// ServletWebServerFactory是TomcatServletWebServerFactory、JettyServletWebServerFactory、
// UndertowServletWebServerFactory的父类
// 所以如果Tomcat被引入，上面的tomcatServletWebServerFactory就会被创建，这里的条件就不满足，不会被创建。
@ConditionalOnClass({ Servlet.class, Server.class, Loader.class, WebAppContext.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedJetty {
@Bean
JettyServletWebServerFactory JettyServletWebServerFactory(
... 代码省略
}
}
// 分析同上
@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedUndertow {
@Bean
UndertowServletWebServerFactory undertowServletWebServerFactory(
... 代码省略
}
}下面继续以Tomcat为例
Tomcat是在Spring容器启动的时候启动的
SpringApplication.run方法
首先创建一个ConfigurableApplicationContext对象，并调用其refresh()方法，这个对象一般是AnnotationConfigServletWebServerApplicationContext。
context = createApplicationContext(); -> refreshContext(context); -> refresh(context); -> applicationContext.refresh();
refresh()方法会调用其父类ServletWebServerApplicationContext的refresh()方法，在父类的refresh()中再次调用父类AbstractApplicationContext的refresh()方法，主要在onRefresh阶段，会进行服务器的配置。
... refresh()代码简略 // 这里会初始化Tomcat配置 onRefresh(); // 这里会启动Tomcat finishRefresh(); ...
回到ServletWebServerApplicationContext类的onRefresh()方法，会调用createWebServer()方法，创建web服务器。
protected void onRefresh() {
super.onRefresh();
try {
// 创建服务器
createWebServer();
}
catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}private void createWebServer() {
... 代码简略
// 获取工厂类，这里获取的就是在配置类中生效的那一个，这里为TomcatServletWebServerFactory
ServletWebServerFactory factory = getWebServerFactory();
createWebServer.tag("factory", factory.getClass().toString());
// 获取服务器
this.webServer = factory.getWebServer(getSelfInitializer());
}TomcatServletWebServerFactory.getWebServer
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());
for (LifecycleListener listener : this.serverLifecycleListeners) {
tomcat.getServer().addLifecycleListener(listener);
}
// 设置Connector，对应与Tomcat Server.xml 中的<Connector></Connector>
Connector connector = new Connector(this.protocol);
connector.setThrowOnFailure(true);
// 对应于Server.xml 中
// <Service name="Catalina">
// <Connector port="8080" protocol="HTTP/1.1"
// connectionTimeout="20000"
// redirectPort="8443" relaxedQueryChars="[|]"/>
// </Service>
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);
}
// 准备好Context组件
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}// 创建Tomcat服务器
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
return new TomcatWebServer(tomcat, getPort() >= 0, getShutdown());
}至此，Tomcat配置已经初始化完成，准备启动。
在finishRefresh()方法中，会启动Tomcat
getLifecycleProcessor().onRefresh(); > DefaultLifecycleProcessor.startBeans(true); > LifecycleGroup::start > doStart(this.lifecycleBeans, member.name, this.autoStartupOnly); > bean.start(); > WebServerStartStopLifecycle.start > TomcatWebServer.start();
private void startBeans(boolean autoStartupOnly) {
Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
Map<Integer, LifecycleGroup> phases = new TreeMap<>();
lifecycleBeans.forEach((beanName, bean) -> {
if (!autoStartupOnly || (bean instanceof SmartLifecycle smartLifecycle && smartLifecycle.isAutoStartup())) {
int phase = getPhase(bean);
phases.computeIfAbsent(
phase,
p -> new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly)
).add(beanName, bean);
}
});
if (!phases.isEmpty()) {
phases.values().forEach(LifecycleGroup::start);
}
}public void start() {
this.webServer.start();
this.running = true;
this.applicationContext
.publishEvent(new ServletWebServerInitializedEvent(this.webServer, this.applicationContext));
}在prepareContext方法中，有一个方法configureContext
configureContext(context, initializersToUse);
configureContext方法，在这里面创建了一个TomcatStarter对象，这个类实现了ServletContainerInitializer接口，所以在容器启动过程中会被调用。
TomcatStarter starter = new TomcatStarter(initializers); context.addServletContainerInitializer(starter, NO_CLASSES);
initializers是Spring自己定义的初始化接口ServletContextInitializer，传入TomcatStarter之后，在onStartup方法中循环调用onStartup方法。
public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException {
try {
for (ServletContextInitializer initializer : this.initializers) {
initializer.onStartup(servletContext);
}
}
...
}需要注意的是，这里的initializers有些传过来的时候是一个函数式接口，在上面的factory.getWebServer(getSelfInitializer());这里传进来的，就是一个函数式接口
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
return this::selfInitialize;
}实际调用在下面这个方法
private void selfInitialize(ServletContext servletContext) throws ServletException {
prepareWebApplicationContext(servletContext);
registerApplicationScope(servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}在此处绕过所有ServletContextInitializer，随后执行它们的onStartup方法。
其中有一个DispatcherServletRegistrationBean，这个类实现了ServletContextInitializer接口，主要是用来添加DispatchServlet。
DispatcherServletAutoConfiguration配置类中有DispatcherServlet，DispatcherServletRegistrationBean两个Bean。
protected static class DispatcherServletRegistrationConfiguration {
@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
// 创建DispatcherServletRegistrationBean，并把dispatcherServlet传进去
DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
webMvcProperties.getServlet().getPath());
registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
multipartConfig.ifAvailable(registration::setMultipartConfig);
return registration;
}
}
protected static class DispatcherServletConfiguration {
@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
// 创建DispatcherServlet
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
return dispatcherServlet;
}
}ServletContextInitializer.onStartup方法由子类RegistrationBean实现
public final void onStartup(ServletContext servletContext) throws ServletException {
String description = getDescription();
if (!isEnabled()) {
logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
return;
}
// register是一个抽象方法，由子类DynamicRegistrationBean实现
register(description, servletContext);
}
protected abstract void register(String description, ServletContext servletContext);DynamicRegistrationBean.register
protected final void register(String description, ServletContext servletContext) {
// addRegistration是一个抽象方法，由子类ServletRegistrationBean实现
D registration = addRegistration(description, servletContext);
if (registration == null) {
logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");
return;
}
// Servlet被添加到Context后，这里对Servlet进行配置，如拦截路径
configure(registration);
}
protected abstract D addRegistration(String description, ServletContext servletContext);ServletRegistrationBean.addRegistration，作用类似下面
<servlet>
<servlet-name>dispatcher</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
</servlet>protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) {
String name = getServletName();
// 添加Servlet到Context中，这里的servlet就是DispatchServlet。
return servletContext.addServlet(name, this.servlet);
}ServletRegistrationBean.configure，作用类似下面
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>protected void configure(ServletRegistration.Dynamic registration) {
super.configure(registration);
String[] urlMapping = StringUtils.toStringArray(this.urlMappings);
if (urlMapping.length == 0 && this.alwaysMapUrl) {
// DEFAULT_MAPPINGS默是“/”
urlMapping = DEFAULT_MAPPINGS;
}
if (!ObjectUtils.isEmpty(urlMapping)) {
// 设置mapping
registration.addMapping(urlMapping);
}
registration.setLoadOnStartup(this.loadOnStartup);
if (this.multipartConfig != null) {
registration.setMultipartConfig(this.multipartConfig);
}
}至此，DispatchServlet已配置好，后续流程和web.xml配置调用流程基本相同。
protected WebApplicationContext initWebApplicationContext() {
// 此处获取根容器，就是Spring初始化的XmlWebApplicationContext，
// 在上面把它添加到了ServletContext的属性中，标记根容器，这里把它获取出来
// String ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE = WebApplicationContext.class.getName() + ".ROOT";
// servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
// ===========上面为使用web.xml时的分析，下面为SpringBoot嵌入式Tomcat分析============
// 同样是获取根容器，不过一般为AnnotationConfigServletWebServerApplicationContext
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
// 此时webApplicationContext还是null，因为DispatchServlet是被tomcat创建的，需要无参构造器
// 构造器中没有设置webApplicationContext的代码，所以此时webApplicationContext还是null
// ===========上面为使用web.xml时的分析，下面为SpringBoot嵌入式Tomcat分析============
// 注意：在SpringBoot使用嵌入式Tomcat时，这个webApplicationContext不为null，因为FrameworkServlet还
// 实现了ApplicationContextAware接口，所以当SpringBoot的上下文准备好之后，会回调setApplicationContext方法
// 注入ApplicationContext，后面在细说
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext cwac && !cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
// 此处主要是获取web.xml配置的WebApplicationContext
// 可以通过设置参数contextAttribute来设置加载SpringMVC的ApplicationContext
// 比如下面这样。除非项目中有多个WebApplicationContext，需要使用其他WebApplicationContext才会用到
// 一般都是null
// <context-param>
// <param-name>contextAttribute</param-name>
// <param-value>myWebApplicationContext</param-value>
// </context-param>
// ===========上面为使用web.xml时的分析，下面为SpringBoot嵌入式Tomcat分析
// 因为wac此时不为null，这里不会进入
wac = findWebApplicationContext();
}
if (wac == null) {
// 现在进入到创建SpringMVC的ApplicationContext流程
// 也就是加载contextConfigLocation定义的xml文件
// ===========上面为使用web.xml时的分析，下面为SpringBoot嵌入式Tomcat分析
// 因为wac此时不为null，这里不会进入，所以没有SpringMVC的容器，也就是没有父子容器之分，SpringBoot项目中只有一个容器
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
synchronized (this.onRefreshMonitor) {
// 初始化策略对象
// 比如：HandlerMapping，HandlerAdapter，ViewResolver等等
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}Das obige ist der detaillierte Inhalt vonweb.xml Mit welcher Methode verpackt SpringBoot ausführbare Jars, um SpringMVC auszuführen?. Für weitere Informationen folgen Sie bitte anderen verwandten Artikeln auf der PHP chinesischen Website!
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