Spring 源码解析一:SpringMVC 的加载机制

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Spring 源码解析一:SpringMVC 的加载机制

1. spring-framework 包含的模块

在解析 SpringMVC 的加载机制之前,先来看看官方 spring-framework 包含有哪些模块,各有什么用。

spring-framework 官方仓库

  • spring-jclspring 框架的通用日志处理
  • spring-corespring 框架的核心机制模块,包括 Java 字节码的操作处理与动态生成、依赖注入机制(也叫控制反转)、工具类库、
    注解操作、编码处理与数据转换、资源加载与处理、环境加载机制等
  • spring-beansspring bean 的定义、加载、解析、编辑等
  • spring-contextspring 框架的上下文环境,包括应用缓存、应用事件、应用配置、核心注解定义与处理、资源加载、异步与定时任务、数据验证与格式化等
  • spring-aop:面向切面编程的封装与处理
  • spring-aspects:使用 AspectJ 作为底层实现的面向切面编程
  • spring-tx:事务的封装与处理
  • spring-jdbc:数据库链接的封装与处理
  • spring-context-indexer:对注解 @Indexed 的支持
  • spring-context-support:对一些第三方库的可选支持,如 ehcache, javamail, quartz, freemarker
  • spring-oxm:对 O/X Mapper 的封装
  • spring-messaging:对 http, rsocket, simp 等消息传递协议的封装
  • spring-jms:对 JMS(Java 消息服务) 的封装
  • spring-expressionSpring Expression Language (SpEL) Spring 表达式语言的实现
  • spring-r2dbc:对 R2DBC 的封装
  • spring-orm:对 JPAhibernate 的封装
  • spring-web:提供了 Web 框架的基础结构与技术,如 Http 的调用、过滤、处理等
  • spring-webmvc:Web MVC 架构的实现,包括 Servlet 容器初始化、路由映射、视图渲染、响应处理等
  • spring-websocket:对 WebSocket 的支持
  • spring-webflux:Reactive Web 框架的实现,与 spring-webmvc 相对

SpringMVC 框架的核心模块主要是:spring-corespring-beansspring-contextspring-webspring-webmvc,后面也主要从这几个模块来解析。

1.1. spring-core

spring-core 的核心功能有几点需要在这里简单介绍一下:

  1. spring-core 有强大的 Java 字节码操作处理功能与动态生成功能,这是面向切面编程、数据类型转换、SpEL 表达式等功能的基础
  2. spring-core 提供了依赖注入机制,这是 spring bean 加载的基础,也是我们可以使用 @Autowired 自动装载对象等功能的底层机制
  3. spring-core 提供了环境加载的机制,所以我们可以使用 application-dev.yml, application-test.yml, application-prod.yml, ...
    来根据环境加载不同的配置
  4. spring-core 提供了一个类似 Java SPI 的的扩展机制,可以自动实例化其他包指定的类,spring-boot, spring-cloud 都依赖这个机制自动加载资源。
    META-INF/spring.factories 文件中定义需要自动加载的类,详细介绍可以参考 Spring Factories

1.2. spring-beans

Spring bean 的加载与扩展机制有几点需要在这里简单介绍一下:

  1. Spring bean 的定义主要是两种:基于注解的定义、基于 XML 文件的定义
  2. spring-beans 提供了基于 XML 配置的、第三方对 bean 的命令空间扩展机制,主要是在
    META-INF/spring.handlers, META-INF/spring.schemas 文件中定义需要扩展的命令空间,
    比如 <dubbo:application name="name"/>, <dubbo:registry address="address"/>
  3. 基于注解的自定义扩展,需要依赖 spring-boot 的扩展加载机制

1.3. spring-context

spring-context 是应用的核心处理部分,包括:

  • 应用缓存
  • 应用事件
  • 应用配置
  • 核心注解定义与处理
  • 资源加载
  • 异步与定时任务
  • 数据验证与格式化

等,@ComponentScan, @Profile, @Conditional, @Bean, @Async, @Controller, @Service, @Component, @Validated 等这类框架核心注解便是在这里定义的。

1.4. spring-web

spring-web 是 Http 的核心处理部分,主要包含:

  • 核心 Http 请求与响应处理(包括 Cookie、缓存、多媒体等)
  • Http 请求与响应编解码与转换(包括 Json、XML、ProtoBuf 等)
  • Reactive Web 框架基础处理
  • 调用客户端(如 RestTemplate
  • Servlet 上下文环境
  • 请求过滤器
  • Multipart 文件上传处理

等,@RequestMapping, @RequestParam, @PathVariable, @ResponseBody, @RestController 等这类 Web 核心注解便是在这里定义的。

1.5. spring-webmvc

spring-webmvc 依赖于 spring-web,主要功能包括:

  • Servlet 容器初始化
  • 路由映射
  • 视图渲染
  • 响应处理

等,如果不使用 Spring MVC ,但想要借助其它 Spring 支持的 web 相关技术的优势,那么只需依赖 spring-web,如 spring-webflux

1.6. spring-webflux

spring-webfluxspring-webmvc 相对应,webmvc 是同步阻塞框架,而 webflux 是异步非阻塞框架,
是 Spring Framework 5.0 中引入的新的响应式 web 框架。

参考:Spring WebFlux 入门
Spring WebFlux :: Spring Docs

2. 一个简单的 spring-webmvc 项目配置

WEB-INF/web.xml 文件中如下配置:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    version="3.0">

  <display-name>springMVC</display-name>

  <!-- 部署 DispatcherServlet -->
  <servlet>
    <servlet-name>springmvc</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:springmvc-servlet.xml</param-value>
    </init-param>
    <!-- 容器再启动时立即加载servlet -->
    <load-on-startup>1</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>springmvc</servlet-name>
    <!-- 处理所有URL -->
    <url-pattern>/</url-pattern>
  </servlet-mapping>

  <!-- 定义应用程序监听器 -->
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
</web-app>

这里有两个入口类:

这两个类分别定义在 spring-webmvcspring-web 中,下面对他们一一进行解析。

3. DispatcherServlet

先来看看 DispatcherServlet 的继承关系:

- javax.servlet.Servlet
  - javax.servlet.GenericServlet
    - javax.servlet.http.HttpServlet
      - HttpServletBean
        - FrameworkServlet
          - DispatcherServlet

3.1. javax.servlet.Servlet

首先看看 javax.servlet.Servlet

javax.servlet.Servlet 主要定义了 2 个方法:

  • init:初始化 Servlet,只执行一次
  • service:响应请求,每次 http 请求都会调用这个方法
public interface Servlet {
    // 初始化 Servlet,只执行一次
    public void init(ServletConfig config) throws ServletException;

    // 响应请求,每次http请求都会调用这个方法
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException;

    // 销毁 Servlet
    public void destroy();
}

3.2. javax.servlet.GenericServlet

再来看看 javax.servlet.GenericServlet

javax.servlet.GenericServlet 主要是重载了 init 方法

public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable {
    public GenericServlet() {}

    // 添加配置初始化
    public void init(ServletConfig config) throws ServletException {
        this.config = config;
        this.init();
    }

    // 保留无参初始化
    public void init() throws ServletException {}

    // 留给子类实现
    public abstract void service(ServletRequest req, ServletResponse res) throws ServletException, IOException;
}

3.3. javax.servlet.http.HttpServlet

再来看看 javax.servlet.http.HttpServlet

javax.servlet.http.HttpServlet 主要是重载了 service 方法,并扩展了 7 个方法:

  • doGet:处理 GET 请求,只输入错误信息,未实现
  • doHead:处理 HEAD 请求,只输入错误信息,未实现
  • doPost:处理 POST 请求,只输入错误信息,未实现
  • doPut:处理 PUT 请求,只输入错误信息,未实现
  • doDelete:处理 DELETE 请求,只输入错误信息,未实现
  • doOptions:处理 OPTIONS 请求
  • doTrace:处理 TRACE 请求
public abstract class HttpServlet extends GenericServlet {
    private static final String METHOD_DELETE = "DELETE";
    private static final String METHOD_HEAD = "HEAD";
    private static final String METHOD_GET = "GET";
    private static final String METHOD_OPTIONS = "OPTIONS";
    private static final String METHOD_POST = "POST";
    private static final String METHOD_PUT = "PUT";
    private static final String METHOD_TRACE = "TRACE";

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_get_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }

    protected void doHead(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        NoBodyResponse response = new NoBodyResponse(resp);
        // 调用 doGet,但body设为空body
        doGet(req, response);
        response.setContentLength();
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        // ... 代码省略
    }

    protected void doPut(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        // ... 代码省略
    }

    protected void doDelete(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        // ... 代码省略
    }

    protected void doOptions(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        // ... 代码省略
    }

    protected void doTrace(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        // ... 代码省略
    }

    // 实现了GET, HEAD, POST PUT, DELETE, OPTIONS, TRACE七个Http方法
    protected void service(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String method = req.getMethod();

        if (method.equals(METHOD_GET)) {
            // ... 代码省略
            doGet(req, resp);
            // ... 代码省略
        } else if (method.equals(METHOD_HEAD)) {
            long lastModified = getLastModified(req);
            maybeSetLastModified(resp, lastModified);
            doHead(req, resp);
        } else if (method.equals(METHOD_POST)) {
            doPost(req, resp);
        } else if (method.equals(METHOD_PUT)) {
            doPut(req, resp);
        } else if (method.equals(METHOD_DELETE)) {
            doDelete(req, resp);
        } else if (method.equals(METHOD_OPTIONS)) {
            doOptions(req,resp);
        } else if (method.equals(METHOD_TRACE)) {
            doTrace(req,resp);
        } else {
            String errMsg = lStrings.getString("http.method_not_implemented");
            Object[] errArgs = new Object[1];
            errArgs[0] = method;
            errMsg = MessageFormat.format(errMsg, errArgs);

            resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
        }
    }

    // 把 Servlet 转化为 HttpServlet
    @Override
    public void service(ServletRequest req, ServletResponse res)
        throws ServletException, IOException
    {
        HttpServletRequest  request;
        HttpServletResponse response;

        if (!(req instanceof HttpServletRequest &&
                res instanceof HttpServletResponse)) {
            throw new ServletException("non-HTTP request or response");
        }

        request = (HttpServletRequest) req;
        response = (HttpServletResponse) res;

        service(request, response);
    }
}

3.4. HttpServletBean

再来看看 HttpServletBean

HttpServletBean 主要是重载了 init 方法,并扩展了 2 个方法:

  • initBeanWrapper:初始化由 Servlet Config 定义的 Java Bean,由子类实现,默认不实现
  • initServletBean:初始化 Servlet bean,由子类实现
public abstract class HttpServletBean extends HttpServlet implements EnvironmentCapable, EnvironmentAware {
    // 初始化
    @Override
    public final void init() throws ServletException {
        // 把Servlet配置参数设置到bean属性中
        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;
            }
        }

        // 初始化Servlet bean
        initServletBean();
    }

    // 初始化由Servlet Config定义的Java Bean,由子类实现,默认不实现
    protected void initBeanWrapper(BeanWrapper bw) throws BeansException {
    }

    // 初始化Servlet bean,由子类实现
    protected void initServletBean() throws ServletException {
    }
}

3.5. FrameworkServlet

再来看看 FrameworkServlet

FrameworkServlet 是框架的核心 Servlet,主要是重载了 initServletBean 方法,并扩展了 2 个方法:

  • initFrameworkServlet:初始化框架 Servlet,由子类实现,默认不实现
  • onRefresh:刷新上下文数据,由子类实现

重载了 service, doGet, doPost, doPut, doDelete, doOptions, doTrace 方法,并扩展了 1 个方法:

  • doService:处理响应请求

3.5.1. FrameworkServlet.initServletBean

父类 HttpServletBean 初始化后,留下两个钩子 initBeanWrapper, initServletBeaninitBeanWrapper 默认并不实现,
所以来看看 initServletBean 钩子的实现:FrameworkServlet.initServletBean

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    @Override
    protected final void initServletBean() throws ServletException {
        // ... 代码省略

        try {
            // 初始化Web应用上下文
            this.webApplicationContext = initWebApplicationContext();
            // 初始化Web框架Servlet
            initFrameworkServlet();
        }
        catch (ServletException | RuntimeException ex) {
            logger.error("Context initialization failed", ex);
            throw ex;
        }

        // ... 代码省略
    }

    // 初始化框架Servlet,由子类实现,默认不实现
    protected void initFrameworkServlet() throws ServletException {}
}

再来看看 FrameworkServlet.initWebApplicationContext

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    protected WebApplicationContext initWebApplicationContext() {
        // 获取应用根上下文
        WebApplicationContext rootContext =
                WebApplicationContextUtils.getWebApplicationContext(getServletContext());
        WebApplicationContext wac = null;

        if (this.webApplicationContext != null) {
            // 对webApplicationContext进行配置
            wac = this.webApplicationContext;
            if (wac instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
                // 未激活
                if (!cwac.isActive()) {
                    if (cwac.getParent() == null) {
                        cwac.setParent(rootContext);
                    }
                    // 配置并刷新应用上下文
                    configureAndRefreshWebApplicationContext(cwac);
                }
            }
        }
        if (wac == null) {
            // 如果没有,则在ServletContext中查找是否注册过
            wac = findWebApplicationContext();
        }
        if (wac == null) {
            // 如果任然没有,则以rootContext为父上下文创建一个新的上下文
            // 并调用 configureAndRefreshWebApplicationContext(cwac) 配置并刷新新的上下文
            // 默认使用 XmlWebApplicationContext(基于XML加载)作为应用上下文
            wac = createWebApplicationContext(rootContext);
        }

        if (!this.refreshEventReceived) {
            // 重载上下文数据
            synchronized (this.onRefreshMonitor) {
                onRefresh(wac);
            }
        }

        if (this.publishContext) {
            // 把上下文注册到ServletContext中
            String attrName = getServletContextAttributeName();
            getServletContext().setAttribute(attrName, wac);
        }

        return wac;
    }


    // 以parent为父上下文创建一个新的上下文
    // 并调用 configureAndRefreshWebApplicationContext(cwac) 配置并刷新新的上下文
    // 默认使用 XmlWebApplicationContext(基于XML加载)作为应用上下文
    protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
        // 这里默认使用 XmlWebApplicationContext(基于XML加载)
        Class<?> contextClass = getContextClass();
        ConfigurableWebApplicationContext wac =
                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

        wac.setEnvironment(getEnvironment());
        wac.setParent(parent);
        String configLocation = getContextConfigLocation();
        if (configLocation != null) {
            wac.setConfigLocation(configLocation);
        }
        configureAndRefreshWebApplicationContext(wac);

        return wac;
    }
}

这其中有两个方法需要深入解析:configureAndRefreshWebApplicationContext, onRefresh

再来看看 FrameworkServlet.configureAndRefreshWebApplicationContext

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
        // ... 代码省略

        // 设置ServletContext
        wac.setServletContext(getServletContext());
        // 设置ServletConfig
        wac.setServletConfig(getServletConfig());
        wac.setNamespace(getNamespace());
        // 添加应用事件监听器,应用事件会触发当前对象的onApplicationEvent方法
        // 进一步,会调用当前对象的onRefresh方法,刷新上下文数据
        wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));

        // ... 代码省略

        // 初始化一些需要初始加载的类,调用这些类的initialize方法
        applyInitializers(wac);
        // 应用上下文刷新
        wac.refresh();
    }

    // 应用事件会触发此方法,然后调用当前对象的onRefresh方法,刷新上下文数据
    public void onApplicationEvent(ContextRefreshedEvent event) {
        this.refreshEventReceived = true;
        synchronized (this.onRefreshMonitor) {
            onRefresh(event.getApplicationContext());
        }
    }
}

再来看看 FrameworkServlet.onRefresh

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    protected void onRefresh(ApplicationContext context) {
        // 由子类来实现
    }
}

3.5.2. FrameworkServlet.service

再来看看 FrameworkServlet.service

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
        // 如果Http方法是Patch或没有,扩展处理
        if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
            processRequest(request, response);
        }
        else {
            super.service(request, response);
        }
    }

    @Override
    protected final void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 扩展处理
        processRequest(request, response);
    }

    @Override
    protected final void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 扩展处理
        processRequest(request, response);
    }

    @Override
    protected final void doPut(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 扩展处理
        processRequest(request, response);
    }

    @Override
    protected final void doDelete(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 扩展处理
        processRequest(request, response);
    }

    @Override
    protected void doOptions(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        if (this.dispatchOptionsRequest || CorsUtils.isPreFlightRequest(request)) {
            // 扩展处理
            processRequest(request, response);
            if (response.containsHeader("Allow")) {
                return;
            }
        }

        // ... 代码省略
    }

    @Override
    protected void doTrace(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        if (this.dispatchTraceRequest) {
            // 扩展处理
            processRequest(request, response);
            if ("message/http".equals(response.getContentType())) {
                return;
            }
        }
        super.doTrace(request, response);
    }
}

再来看看扩展处理方法 FrameworkServlet.processRequest

public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // ... 代码省略

        // 记录请求属性与上下文环境,请求处理完后派发事件
        LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
        LocaleContext localeContext = buildLocaleContext(request);

        RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
        ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());

        initContextHolders(request, localeContext, requestAttributes);

        try {
            doService(request, response);
        }
        // ... 代码省略

        finally {
            resetContextHolders(request, previousLocaleContext, previousAttributes);
            if (requestAttributes != null) {
                requestAttributes.requestCompleted();
            }
            logResult(request, response, failureCause, asyncManager);
            publishRequestHandledEvent(request, response, startTime, failureCause);
        }
    }

    // 由子类来实现
    protected abstract void doService(HttpServletRequest request, HttpServletResponse response)
            throws Exception;
}

3.6. DispatcherServlet

DispatcherServlet 主要扩展了 2 个方法:onRefreshdoService,所以来看看 DispatcherServlet
是如何实现的

3.6.1. DispatcherServlet.onRefresh

DispatcherServlet.onRefresh

public class DispatcherServlet extends FrameworkServlet {
    @Override
    protected void onRefresh(ApplicationContext context) {
        initStrategies(context);
    }

    protected void initStrategies(ApplicationContext context) {
        // 初始化Multipart文件上传处理
        initMultipartResolver(context);
        // 初始化本地化处理
        initLocaleResolver(context);
        // 初始化主题处理
        initThemeResolver(context);
        // 初始化处理器映射
        initHandlerMappings(context);
        // 初始化处理器适配
        initHandlerAdapters(context);
        // 初始化处理器异常
        initHandlerExceptionResolvers(context);
        // 初始化视图查找处理
        initRequestToViewNameTranslator(context);
        // 初始化视图解析处理
        initViewResolvers(context);
        // 初始化内存暂存session数据管理器
        initFlashMapManager(context);
    }

    private void initMultipartResolver(ApplicationContext context) {
        try {
            // 获取bean
            this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);

            // ... 代码省略
        }
        catch (NoSuchBeanDefinitionException ex) {
            // ... 代码省略
        }
    }

    private void initLocaleResolver(ApplicationContext context) {
        try {
            // 获取bean
            this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);

            // ... 代码省略
        }
        catch (NoSuchBeanDefinitionException ex) {
            // ... 代码省略
        }
    }

    private void initThemeResolver(ApplicationContext context) {
        try {
            // 获取bean
            this.themeResolver = context.getBean(THEME_RESOLVER_BEAN_NAME, ThemeResolver.class);

            // ... 代码省略
        }
        catch (NoSuchBeanDefinitionException ex) {
            // ... 代码省略
        }
    }

    private void initFlashMapManager(ApplicationContext context) {
        try {
            // 获取bean
            this.flashMapManager = context.getBean(FLASH_MAP_MANAGER_BEAN_NAME, FlashMapManager.class);
        }
        catch (NoSuchBeanDefinitionException ex) {
            // 没有bean,则获取默认策略
            this.flashMapManager = getDefaultStrategy(context, FlashMapManager.class);
        }
    }
}
3.6.1.1. DispatcherServlet.initHandlerMappings

DispatcherServlet.initHandlerMappings

public class DispatcherServlet extends FrameworkServlet {
    private void initHandlerMappings(ApplicationContext context) {
        this.handlerMappings = null;

        // 默认是探测所有的HandlerMapping,包括父上下文
        if (this.detectAllHandlerMappings) {
            Map<String, HandlerMapping> matchingBeans =
                    BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerMappings = new ArrayList<>(matchingBeans.values());
                AnnotationAwareOrderComparator.sort(this.handlerMappings);
            }
        }
        else {
            // 否则直接获取bean
            try {
                HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
                this.handlerMappings = Collections.singletonList(hm);
            }
            catch (NoSuchBeanDefinitionException ex) {}
        }

        // 如果以上两种都没有定义,则获取默认的处理策略
        if (this.handlerMappings == null) {
            this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
        }

        // ... 代码省略
    }

    // 获取默认的处理策略
    protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
        // 尝试从DispatcherServlet.properties文件中加载
        if (defaultStrategies == null) {
            try {
                ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
                defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
            }
            catch (IOException ex) {
                throw new IllegalStateException("Could not load '" + DEFAULT_STRATEGIES_PATH + "': " + ex.getMessage());
            }
        }

        String key = strategyInterface.getName();
        String value = defaultStrategies.getProperty(key);
        if (value != null) {
            String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
            List<T> strategies = new ArrayList<>(classNames.length);
            for (String className : classNames) {
                try {
                    Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
                    // 创建bean
                    Object strategy = createDefaultStrategy(context, clazz);
                    // 装载到 strategies 中
                    strategies.add((T) strategy);
                }
                catch (ClassNotFoundException ex) {
                    // ... 代码省略
                }
                catch (LinkageError err) {
                    // ... 代码省略
                }
            }
            return strategies;
        }
        else {
            return Collections.emptyList();
        }
    }

    // 创建bean
    protected Object createDefaultStrategy(ApplicationContext context, Class<?> clazz) {
        return context.getAutowireCapableBeanFactory().createBean(clazz);
    }
}

DispatcherServlet.properties
文件(开发者不能自定义覆盖)如下:

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
    org.springframework.web.servlet.function.support.RouterFunctionMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
    org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
    org.springframework.web.servlet.function.support.HandlerFunctionAdapter


org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
    org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
    org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

DispatcherServlet.properties 文件中指明:

3.6.1.2. DispatcherServlet.initHandlerAdapters

DispatcherServlet.initHandlerAdapters

public class DispatcherServlet extends FrameworkServlet {
    private void initHandlerAdapters(ApplicationContext context) {
        this.handlerAdapters = null;

        // 默认是探测所有的HandlerAdapter,包括父上下文
        if (this.detectAllHandlerAdapters) {
            Map<String, HandlerAdapter> matchingBeans =
                    BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerAdapters = new ArrayList<>(matchingBeans.values());
                AnnotationAwareOrderComparator.sort(this.handlerAdapters);
            }
        }
        else {
            // 否则直接获取bean
            try {
                HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
                this.handlerAdapters = Collections.singletonList(ha);
            }
            catch (NoSuchBeanDefinitionException ex) {}
        }

        // 如果以上两种都没有定义,则获取默认的处理策略
        if (this.handlerAdapters == null) {
            this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
        }
    }
}
3.6.1.3. DispatcherServlet.initHandlerExceptionResolvers

DispatcherServlet.initHandlerExceptionResolvers

public class DispatcherServlet extends FrameworkServlet {
    private void initHandlerExceptionResolvers(ApplicationContext context) {
        this.handlerExceptionResolvers = null;

        // 默认是探测所有的HandlerExceptionResolver,包括父上下文
        if (this.detectAllHandlerExceptionResolvers) {
            Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
                    .beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
                AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
            }
        }
        else {
            // 否则直接获取bean
            try {
                HandlerExceptionResolver her =
                        context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
                this.handlerExceptionResolvers = Collections.singletonList(her);
            }
            catch (NoSuchBeanDefinitionException ex) {}
        }

        // 如果以上两种都没有定义,则获取默认的处理策略
        if (this.handlerExceptionResolvers == null) {
            this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
        }
    }
}
3.6.1.4. DispatcherServlet.initRequestToViewNameTranslator

DispatcherServlet.initRequestToViewNameTranslator

public class DispatcherServlet extends FrameworkServlet {
    private void initRequestToViewNameTranslator(ApplicationContext context) {
        try {
            // 获取bean
            this.viewNameTranslator =
                    context.getBean(REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME, RequestToViewNameTranslator.class);
        }
        catch (NoSuchBeanDefinitionException ex) {
            // 如果没有定义bean,则获取默认的处理策略
            this.viewNameTranslator = getDefaultStrategy(context, RequestToViewNameTranslator.class);
        }
    }
}
3.6.1.5. DispatcherServlet.initViewResolvers

DispatcherServlet.initViewResolvers

public class DispatcherServlet extends FrameworkServlet {
    private void initViewResolvers(ApplicationContext context) {
        this.viewResolvers = null;

        // 默认是探测所有的ViewResolver,包括父上下文
        if (this.detectAllViewResolvers) {
            Map<String, ViewResolver> matchingBeans =
                    BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.viewResolvers = new ArrayList<>(matchingBeans.values());
                AnnotationAwareOrderComparator.sort(this.viewResolvers);
            }
        }
        else {
            // 否则直接获取bean
            try {
                ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
                this.viewResolvers = Collections.singletonList(vr);
            }
            catch (NoSuchBeanDefinitionException ex) {}
        }

        // 如果以上两种都没有定义,则获取默认的处理策略
        if (this.viewResolvers == null) {
            this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
        }
    }
}

3.6.2. DispatcherServlet.doService

刚刚解析完了 DispatcherServlet.onRefresh,现在来看看 DispatcherServlet.doService

public class DispatcherServlet extends FrameworkServlet {
    @Override
    protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        // ... 代码省略

        // 给请求对象添加一些上下文数据
        request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
        request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
        request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
        request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

        // ... 代码省略

        try {
            doDispatch(request, response);
        }
        finally {
            // ... 代码省略
        }
    }

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        // 处理器链
        HandlerExecutionChain mappedHandler = null;
        // 是Multipart文件上传
        boolean multipartRequestParsed = false;
        // 异步处理管理器
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;

            try {
                // 检测Multipart文件上传
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // 获取处理器,从handlerMappings中查找符合请求的处理器
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
                    // 未找到处理器,404
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // 获取处理器适配器,从handlerAdapters中查找符合处理器的适配器
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                String method = request.getMethod();

                // 如果是GET或HEAD请求,检查Last-Modified
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }

                // 前置处理,调用处理器的preHandle方法,如果有一个不成功,返回
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // 调用处理器
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                // ... 代码省略

                // 如果没有视图名字,添加默认的视图名
                applyDefaultViewName(processedRequest, mv);
                // 后置处理,调用处理器的postHandle方法
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                // ... 代码省略
            }
            catch (Throwable err) {
                // ... 代码省略
            }

            // 处理handler返回的结果
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            // ... 代码省略
        }
        catch (Throwable err) {
            // ... 代码省略
        }
        finally {
            // ... 代码省略
        }
    }

    // 处理handler返回的结果
    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
            @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
            @Nullable Exception exception) throws Exception {

        boolean errorView = false;

        if (exception != null) {
            // ... 代码省略,如果有异常,调用handlerExceptionResolvers处理
        }

        if (mv != null && !mv.wasCleared()) {
            // 渲染视图
            render(mv, request, response);
            if (errorView) {
                WebUtils.clearErrorRequestAttributes(request);
            }
        }
        // ... 代码省略
    }

    // 渲染视图
    protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
        // ... 代码省略

        View view;
        String viewName = mv.getViewName();
        if (viewName != null) {
            // 调用viewResolvers来解析视图
            view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
            // ... 代码省略
        }
        else {
            // ... 代码省略
        }

        // ... 代码省略
        try {
            if (mv.getStatus() != null) {
                // 设置http状态码
                response.setStatus(mv.getStatus().value());
            }
            // 真实渲染
            view.render(mv.getModelInternal(), request, response);
        }
        catch (Exception ex) {
            // ... 代码省略
        }
    }
}

3.6.3. 需要后面再解析的几个点

DispatcherServlet 这个类的解析基本上就差不多了,但还有几点没有解析:

这几点,我们后面再来解析。

4. ContextLoaderListener

先来看看 ContextLoaderListener 的继承关系:

- ContextLoader
  - ContextLoaderListener

ContextLoaderListener
比较简单,只有两个监听事件方法

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent event) {
        // ContextLoader.initWebApplicationContext
        initWebApplicationContext(event.getServletContext());
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        // ContextLoader.closeWebApplicationContext
        closeWebApplicationContext(event.getServletContext());
        // 销毁上下文中以"org.springframework."开头的可销毁bean
        ContextCleanupListener.cleanupAttributes(event.getServletContext());
    }
}

ContextLoader
的静态初始化

public class ContextLoader {
    static {
        try {
            // 从ContextLoader.properties文件中加载默认的策略
            ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
            defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
        }
        catch (IOException ex) {
            throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
        }
    }
}

ContextLoader.properties
文件的内容如下:

# Default WebApplicationContext implementation class for ContextLoader.
# Used as fallback when no explicit context implementation has been specified as context-param.
# Not meant to be customized by application developers.

org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

ContextLoader.properties 文件中指明使用 XmlWebApplicationContext 作为默认的 Web 应用上下文环境

再来看看 ContextLoader
initWebApplicationContextcloseWebApplicationContext

4.1. ContextLoaderListener.initWebApplicationContext

ContextLoaderListener.initWebApplicationContext

public class ContextLoader {
    public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
        // ... 代码省略

        try {
            // 如果没有上下文对象,则创建一个新的上下文
            // 并调用 configureAndRefreshWebApplicationContext(cwac) 配置并刷新新的上下文
            // 默认使用 XmlWebApplicationContext(基于XML加载)作为应用上下文
            if (this.context == null) {
                this.context = createWebApplicationContext(servletContext);
            }
            if (this.context instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
                // 未激活
                if (!cwac.isActive()) {
                    if (cwac.getParent() == null) {
                        ApplicationContext parent = loadParentContext(servletContext);
                        cwac.setParent(parent);
                    }
                    // 配置并刷新应用上下文
                    configureAndRefreshWebApplicationContext(cwac, servletContext);
                }
            }

            // 把上下文注册到ServletContext中
            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

            // ... 代码省略

            return this.context;
        }
        catch (RuntimeException | Error ex) {
            // ... 代码省略
        }
    }
}

ContextLoader.configureAndRefreshWebApplicationContextFrameworkServlet.configureAndRefreshWebApplicationContext
的处理基本上一致。

也就是说,当容器启动(如 Tomcat、Jetty、Undertow 等)时,Spring 框架会自动进行初始化。

4.2. ContextLoaderListener.closeWebApplicationContext

ContextLoaderListener.closeWebApplicationContext

public class ContextLoader {
    public void closeWebApplicationContext(ServletContext servletContext) {
        try {
            if (this.context instanceof ConfigurableWebApplicationContext) {
                // 调用上下文对象的close方法
                ((ConfigurableWebApplicationContext) this.context).close();
            }
        }
        finally {
            // ... 代码省略
        }
    }
}

5. 综述

DispatcherServlet.initContextLoaderListener.contextInitialized 都会进行应用上下文的初始化,主要过程是:

  1. 初始化 Web 应用上下文,默认使用 XmlWebApplicationContext(基于 XML 加载)作为应用上下文,并调用 refresh 方法
  2. 实例化由 globalInitializerClassescontextInitializerClasses 定义的类
  3. 实例化 WebMVC 必要的组件:MultipartResolver, LocaleResolver, ThemeResolver, HandlerMapping,
    HandlerAdapter, HandlerExceptionResolver, RequestToViewNameTranslator, ViewResolver, FlashMapManager

每个请求都会进入到 DispatcherServlet.service,其主要过程是:

  1. 初始化请求对象,以便应用后续处理
  2. 处理 Multipart 文件上传,获取处理器处理当前请求
  3. 如果当前请求处理发生异常,进行异常处理
  4. 进行视图渲染

6. 未完

到这里为止,解析仅仅止于 DispatcherServletContextLoaderListener 两个类,下一篇将深入其他类,继续探索。

  • ConfigurableWebApplicationContext.refresh 刷新上下文
  • ApplicationContext.getBean 从上下文中获取 bean
  • DispatcherServlet.properties 文件中定义的策略处理
  • ContextLoader.properties 文件中定义的策略处理
  • View.render 视图渲染

后续

更多博客,查看 https://github.com/senntyou/blogs

作者:深予之 (@senntyou)

版权声明:自由转载-非商用-非衍生-保持署名(创意共享 3.0 许可证

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