SpringBoot中WEB的啟動流程分析
更新時間：2022年03月30日 12:02:02 作者：這是一條海魚
今天我們就來分析下springboot啟動web項目整個流程，本文通過實例代碼給大家介紹的非常詳細(xì)，對大家的學(xué)習(xí)或工作具有一定的參考借鑒價值，需要的朋友參考下吧
想必大家都體驗過springboot的便捷，以前想要運行web項目，我們首先需要將項目打成war包，然后再運行Tomcat啟動項目，不過自從有了springboot，我們可以像啟動jar包一樣簡單的啟動一個web項目，今天我們就來分析下springboot啟動web項目整個流程。
老規(guī)矩，我們從spring.factories文件開始。
spring-boot-starter-web下沒有spring.factories文件
所以我們從spring-boot-autoconfigure下的spring.factories開始
一、DispatcherServlet的注冊
1.1 把DispatcherServlet注入IOC容器
DispatcherServlet是通過DispatcherServletAutoConfiguration注冊的
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {
public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";
@Configuration(proxyBeanMethods = false)
@Conditional(DefaultDispatcherServletCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })
protected static class DispatcherServletConfiguration {
@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet(HttpProperties httpProperties, WebMvcProperties webMvcProperties) {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
dispatcherServlet.setEnableLoggingRequestDetails(httpProperties.isLogRequestDetails());
return dispatcherServlet;
}
@Bean
@ConditionalOnBean(MultipartResolver.class)
@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
public MultipartResolver multipartResolver(MultipartResolver resolver) {
// Detect if the user has created a MultipartResolver but named it incorrectly
return resolver;
}
}
@Configuration(proxyBeanMethods = false)
@Conditional(DispatcherServletRegistrationCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
@Import(DispatcherServletConfiguration.class)
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) {
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;
}
}
@Order(Ordered.LOWEST_PRECEDENCE - 10)
private static class DefaultDispatcherServletCondition extends SpringBootCondition {
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
ConditionMessage.Builder message = ConditionMessage.forCondition("Default DispatcherServlet");
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
List<String> dispatchServletBeans = Arrays
.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
if (dispatchServletBeans.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
return ConditionOutcome
.noMatch(message.found("dispatcher servlet bean").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
if (beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
return ConditionOutcome.noMatch(
message.found("non dispatcher servlet bean").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
if (dispatchServletBeans.isEmpty()) {
return ConditionOutcome.match(message.didNotFind("dispatcher servlet beans").atAll());
}
return ConditionOutcome.match(message.found("dispatcher servlet bean", "dispatcher servlet beans")
.items(Style.QUOTE, dispatchServletBeans)
.append("and none is named " + DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
}
@Order(Ordered.LOWEST_PRECEDENCE - 10)
private static class DispatcherServletRegistrationCondition extends SpringBootCondition {
@Override
public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
ConditionOutcome outcome = checkDefaultDispatcherName(beanFactory);
if (!outcome.isMatch()) {
return outcome;
}
return checkServletRegistration(beanFactory);
}
private ConditionOutcome checkDefaultDispatcherName(ConfigurableListableBeanFactory beanFactory) {
List<String> servlets = Arrays
.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
boolean containsDispatcherBean = beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
if (containsDispatcherBean && !servlets.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
return ConditionOutcome.noMatch(
startMessage().found("non dispatcher servlet").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
}
return ConditionOutcome.match();
}
private ConditionOutcome checkServletRegistration(ConfigurableListableBeanFactory beanFactory) {
ConditionMessage.Builder message = startMessage();
List<String> registrations = Arrays
.asList(beanFactory.getBeanNamesForType(ServletRegistrationBean.class, false, false));
boolean containsDispatcherRegistrationBean = beanFactory
.containsBean(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
if (registrations.isEmpty()) {
if (containsDispatcherRegistrationBean) {
return ConditionOutcome.noMatch(message.found("non servlet registration bean")
.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
return ConditionOutcome.match(message.didNotFind("servlet registration bean").atAll());
}
if (registrations.contains(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)) {
return ConditionOutcome.noMatch(message.found("servlet registration bean")
.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
if (containsDispatcherRegistrationBean) {
return ConditionOutcome.noMatch(message.found("non servlet registration bean")
.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
return ConditionOutcome.match(message.found("servlet registration beans").items(Style.QUOTE, registrations)
.append("and none is named " + DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
}
private ConditionMessage.Builder startMessage() {
return ConditionMessage.forCondition("DispatcherServlet Registration");
}
}
}
這也是SpringBoot中IOC容器和WEB容器是同一個的原因
Spring把DispatcherServlet放到容器中后，在DispatcherServlet的初始化中會執(zhí)行ApplicationContextAwareProcessor的postProcessBeforeInitialization方法，而其postProcessBeforeInitialization底層如下
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof EnvironmentAware) {
((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
}
if (bean instanceof EmbeddedValueResolverAware) {
((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
}
if (bean instanceof ResourceLoaderAware) {
((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
}
if (bean instanceof ApplicationEventPublisherAware) {
((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
}
if (bean instanceof MessageSourceAware) {
((MessageSourceAware) bean).setMessageSource(this.applicationContext);
}
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}
而DispatcherServlet是一個ApplicationContextAware，所以會執(zhí)行其setApplicationContext方法，設(shè)置其屬性webApplicationContext
@Override
public void setApplicationContext(ApplicationContext applicationContext) {
//傳入ioc容器
if (this.webApplicationContext == null && applicationContext instanceof WebApplicationContext) {
this.webApplicationContext = (WebApplicationContext) applicationContext;
this.webApplicationContextInjected = true;
}
}
所以在web容器啟動過程會把web容器設(shè)置成和ioc容器一樣，springMVC容器創(chuàng)建代碼如下，參考文章springMVC全注解啟動和容器的初始化
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
//因為webApplicationContext這里有值了，所以會進入這里
if (this.webApplicationContext != null) {
//把web容器設(shè)置成和ioc容器一樣
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
if (cwac.getParent() == null)
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
wac = findWebApplicationContext();
wac = createWebApplicationContext(rootContext);
if (!this.refreshEventReceived) {
synchronized (this.onRefreshMonitor) {
onRefresh(wac);
if (this.publishContext) {
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
return wac;
}
這里可能要有人問了，為什么在springMVC環(huán)境中，this.webApplicationContext為null,因為在springMVC中DispatcherServlet沒有通過spring容器管理
protected void registerDispatcherServlet(ServletContext servletContext) {
String servletName = getServletName();
Assert.hasLength(servletName, "getServletName() must not return null or empty");
//創(chuàng)建web容器
WebApplicationContext servletAppContext = createServletApplicationContext();
Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");
//創(chuàng)建DispatcherServlet對象
FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null");
dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());
//把dispatcherServlet作為Servlet注冊到上下文中
ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
if (registration == null) {
throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +
"Check if there is another servlet registered under the same name.");
}
//容器在啟動的時候加載這個servlet，其優(yōu)先級為1（正數(shù)的值越小，該servlet的優(yōu)先級越高，應(yīng)用啟動時就越先加載）
registration.setLoadOnStartup(1);
//設(shè)置Servlet映射mapping路徑
//getServletMappings()是模版方法，需要我們自己配置
registration.addMapping(getServletMappings());
//設(shè)置是否支持異步請求
//isAsyncSupported默認(rèn)是true
registration.setAsyncSupported(isAsyncSupported());
//處理自定義的Filter進來，一般我們Filter不這么加進來，而是自己@WebFilter，或者借助Spring，
//備注：這里添加進來的Filter都僅僅只攔截過濾上面注冊的dispatchServlet
Filter[] filters = getServletFilters();
if (!ObjectUtils.isEmpty(filters)) {
for (Filter filter : filters) {
registerServletFilter(servletContext, filter);
}
}
//這個很清楚：調(diào)用者若相對dispatcherServlet有自己更個性化的參數(shù)設(shè)置，復(fù)寫此方法即可
customizeRegistration(registration);
}
1.2 把DispatcherServlet注入Servlet容器
SpringBoot中容器是AnnotationConfigServletWebServerApplicationContext，其onRefresh()方法如下
@Override
protected void onRefresh() {
super.onRefresh();
try {
createWebServer(); //創(chuàng)建Servlet容器
}
catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
if (webServer == null && servletContext == null) {
ServletWebServerFactory factory = getWebServerFactory();
this.webServer = factory.getWebServer(getSelfInitializer());//創(chuàng)建容器，并執(zhí)行所有ServletContextInitializer的onStartup
}
else if (servletContext != null) {
try {
getSelfInitializer().onStartup(servletContext);
}
catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context", ex);
}
}
initPropertySources();
}
注意，這里他不會執(zhí)行SpringServletContainerInitializer。
流程如下
1、通過getSelfInitializer()方法執(zhí)行容器中所有的ServletContextInitializer
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
return this::selfInitialize;
}
private void selfInitialize(ServletContext servletContext) throws ServletException {
prepareWebApplicationContext(servletContext);
registerApplicationScope(servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
而ServletContextInitializer有個子類ServletRegistrationBean，通過其addRegistration方法注入Servlet容器中
@Override
protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) {
String name = getServletName();
return servletContext.addServlet(name, this.servlet);
}
到此這篇關(guān)于SpringBoot中WEB的啟動的文章就介紹到這了,更多相關(guān)SpringBoot WEB啟動內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！
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