SpringBoot中Tomcat和SpringMVC整合源码分析

org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration.ConditionalOnClass=javax.servlet.ServletRequest
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration.ConditionalOnWebApplication=SERVLET
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration.AutoConfigureOrder=-2147483648

@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
// 判断是否有 ServletRequest 类
@ConditionalOnClass(ServletRequest.class)
// 判断 WebApplication 是 SERVLET 容器
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <version>2.2.5.RELEASE</version>
    <scope>compile</scope>
</dependency>

// 导入具体服务器类
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsReGIStrar.class,
         ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
         ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
         ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })

@Configuration(proxyBeanMethods = false)
#当前工程下需要有Servlet、Tomcat UpgradeProtocol类
@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
#当前的Spring容器类不能有ServletWebServerFactory类型的Bean，搜索的是当前容器。
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
static class EmbeddedTomcat {
    @Bean
    TomcatServletWebServerFactory tomcatServletWebServerFactory(
        ObjectProvider<TomcatConnectorCustomizer> connectorCustomizers,
        ObjectProvider<TomcatContextCustomizer> contextCustomizers,
        ObjectProvider<TomcatProtocolHandlerCustomizer<?>> protocolHandlerCustomizers) {
        // 创建 TomcatServletWebServerFactory ，是产生TomcatServletWebServer的工厂类
        TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
        factory.getTomcatConnectorCustomizers()
            .addAll(connectorCustomizers.orderedStream().collect(Collectors.toList()));
        factory.getTomcatContextCustomizers()
            .addAll(contextCustomizers.orderedStream().collect(Collectors.toList()));
        factory.getTomcatProtocolHandlerCustomizers()
            .addAll(protocolHandlerCustomizers.orderedStream().collect(Collectors.toList()));
        return factory;
    }
}

<servlet>
    <servlet-name>dispatcherServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:springmvc.xml</param-value>
            </init-param>
            <!--Web服务器一旦启动，Servlet就会实例化创建对象，然后初始化(预备创建对象)-->
            <load-on-startup>1</load-on-startup>
</servlet>

#WebApplication是SERVLET容器
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration.ConditionalOnWebApplication=SERVLET
#工程中需要引入 DispatcherServlet 类
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration.ConditionalOnClass=org.springframework.web.servlet.DispatcherServlet
#容器注入在 ServletWebServerFactoryAutoConfiguration（服务器自动配置类） 类之后，
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration.AutoConfigureAfter=org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration.AutoConfigureOrder=-2147483648

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)

@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;
    }
}

@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;
    }
}

#工程中需要引入Servlet、WebMvcConfigurer、 DispatcherServlet类 org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.ConditionalOnClass=javax.servlet.Servlet,org.springframework.web.servlet.config.annotation.WebMvcConfigurer,org.springframework.web.servlet.DispatcherServlet
# 容器注入在 DispatcherServletAutoConfiguration、TaskExecutionAutoConfiguration、ValidationAutoConfiguration之
# 后
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.AutoConfigureAfter=org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.AutoConfigureOrder=-2147483638

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.2.4.RELEASE</version>
    <scope>compile</scope>
</dependency>

protected void onRefresh() {
    super.onRefresh();
    try {
        // 创建 web 服务器
        createWebServer();
    }
    catch (Throwable ex) {
        throw new ApplicationContextException("Unable to start web server", ex);
    }
}

private void createWebServer() {
    WebServer webServer = this.webServer;
    ServletContext servletContext = getServletContext();
    // 如果为 null，则创建
    if (webServer == null && servletContext == null) {
        // 获取WebServerFactory
        ServletWebServerFactory factory = getWebServerFactory();
       // 获取 webServer ，getSelfInitializer() 返回的是 函数式接口
	   // 是一个 实现了@FunctionalInterface 接口的列表
        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();
}

protected ServletWebServerFactory getWebServerFactory() {
    // 先获 BeanFactory ，再从 BeanFactory取 ServletWebServerFactory 类型的 BeanNames
    String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
    // 如果长度为 0，则抛异常
    if (beanNames.length == 0) {
        throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
                                              + "ServletWebServerFactory bean.");
    }
    // 如果长度大于 1，则抛异常
    if (beanNames.length > 1) {
        throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
                                              + "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
    }
    // 返回根据第一个beanName和ServletWebServerFactory类型获取容器中的Bean
    return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}

@FunctionalInterface
public interface ServletContextInitializer {
	
	void onStartup(ServletContext servletContext) throws ServletException;
}

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

private void selfInitialize(ServletContext servletContext) throws ServletException {
    prepareWebApplicationContext(servletContext);
    registerApplicationScope(servletContext);
    // 注入 servletContext 类型的 bean
    WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
    // 注入实现了ServletContextInitializer 接口的类 ，并进行循环调用onStartup
    for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
        beans.onStartup(servletContext);
    }
}

//getServletContextInitializerBeans具体代码
protected Collection<ServletContextInitializer> getServletContextInitializerBeans() {
    // 构造ServletContextInitializerBeans对象，该对象实现了 AbstractCollection<ServletContextInitializer> 接口
    // 是 ServletContextInitializer的 一个集合类。
    return new ServletContextInitializerBeans(getBeanFactory());
}

// ServletContextInitializerBeans 构造方法
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
                                      Class<? extends ServletContextInitializer>... initializerTypes) {
    // 初始化 initializers
    this.initializers = new LinkedMultiValueMap<>();
    this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
        : Collections.singletonList(ServletContextInitializer.class);
    // 在beanFactory中查找实现了 ServletContextInitializer 接口的类
    // 这里包括了  ServletRegistrationBean 、FilterRegistrationBean
    // DelegatingFilterProxyRegistrationBean、ServletListenerRegistrationBean 和其他。
    // 添加到 initializers 集合中
    addServletContextInitializerBeans(beanFactory);
    // 添加适配的 Bean
    addAdaptableBeans(beanFactory);
    // initializers 排序
    List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
        .flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
        .collect(Collectors.toList());
    // 给该集合可遍历对象赋值
    this.sortedList = Collections.unmodifiableList(sortedInitializers);
    // 返回 initializers
    logMappings(this.initializers);
}

public final void onStartup(ServletContext servletContext) throws ServletException {
    String description = getDescription();
    if (!isEnabled()) {
        logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
        return;
    }
    // 注册 Servlet 到 tomcat的 servletContext中
    register(description, servletContext);
}

@Override
protected final void register(String description, ServletContext servletContext) {
    // 添加当前的 servlet 到 tomcat 的 servletContext 中
    D registration = addRegistration(description, servletContext);
    if (registration == null) {
        logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");
        return;
    }
    configure(registration);
}

@Override
protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) {
    // 获取 当前对象的 servlet 名称
    String name = getServletName();
    //添加当前的 servlet 到 tomcat 的 servletContext 中
    return servletContext.addServlet(name, this.servlet);
}

public WebServer getWebServer(ServletContextInitializer... initializers) {
    if (this.disableMBeanRegistry) {
        Registry.disableRegistry();
    }
    // 创建具体的Tomcat类
    Tomcat tomcat = new Tomcat();
    // 获取主路径，并且设置主路径
    File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
    tomcat.setBaseDir(baseDir.getAbsolutePath());
    // 创建连接器和协议
    Connector connector = new Connector(this.protocol);
    connector.setThrowOnFailure(true);
    // 添加连接器
    tomcat.getService().addConnector(connector);
    customizeConnector(connector);
    tomcat.setConnector(connector);
    // 设置 host 的自动部署属性为 false
    tomcat.getHost().setAutoDeploy(false);
    // 配置 engine
    configureEngine(tomcat.getEngine());
    for (Connector additionalConnector : this.additionalTomcatConnectors) {
        tomcat.getService().addConnector(additionalConnector);
    }
    // 初始化 TomcatEmbeddedContext ，并把 TomcatEmbeddedContext 添加至 host 中
	// 用 initializersToUse 初始化 TomcatStarter ，并设置 TomcatEmbeddedContext 的Starter属性为  TomcatStarter 
    // initializersToUse 为函数式接口 ，即 实现了ServletContextInitializer接口 的匿名类
    prepareContext(tomcat.getHost(), initializers);
    // 创建具体的 TomcatwebServer
    return getTomcatWebServer(tomcat);
}

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;
    // 自动开启
    this.autoStart = autoStart;
    // 初始化方法
    initialize();
}

// Start the server to trigger initialization listeners
// tomcat 服务器启动
this.tomcat.start();

public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException {
    try {
        // 遍历已经注册的 initializers， 
        for (ServletContextInitializer initializer : this.initializers) {
            initializer.onStartup(servletContext);
        }
    }
    catch (Exception ex) {
        this.startUpException = ex;
        // Prevent Tomcat from logging and re-throwing when we know we can
        // deal with it in the main thread, but log for infORMation here.
        if (logger.isErrorEnabled()) {
            logger.error("Error starting Tomcat context. Exception: " + ex.getClass().getName() + ". Message: "
                         + ex.getMessage());
        }
    }
}