前言:

下面,我们将演示如何搭建一个纯注解配置的springmvc,并通过跟踪源码的方式解析随着应用服务器的启动我们的springmvc配置是如何生效的。使用web容器版本:apache-tomcat-8.5.27 。代码中一些不重要的内容未展示。

正文:

1. 编写一个简单的web应用:

maven依赖:

per.ym
  mvcdemo
  0.0.1-SNAPSHOT
  war

  mvcdemo
  http://maven.apache.org

  
    UTF-8
    UTF-8
    1.8
    1.8
    1.8
  

  
    
      junit
      junit
      3.8.1
      test
    

    
        org.springframework
        spring-webmvc
        4.3.20.RELEASE
    

    
    
        org.springframework
        spring-web
        4.3.20.RELEASE
    

    
        javax.servlet
        javax.servlet-api
        3.1.0
    
  

  
  
    
        org.apache.maven.plugins
        maven-war-plugin
        2.2
        
          WebContent\WEB-INF\web.xml
        
    
  
  

springmvc配置类:

package per.ym.mvcdemo.config;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class[] getRootConfigClasses() {
        return new Class[] {RootConfig.class};
    }

    @Override
    protected Class[] getServletConfigClasses() {
        return new Class[] {WebConfig.class};
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] {"/"};
    }

    @Override
    protected Filter[] getServletFilters() {
        return null;
    }

    @Override
    protected void customizeRegistration(ServletRegistration.Dynamic registration) {
        registration.setMultipartConfig(new MultipartConfigElement("/temp/uploads"));
    }
}

root:

package per.ym.mvcdemo.config;

@Configuration
@ComponentScan(basePackages = "per.ym.mvcdemo.service",
        excludeFilters = {@Filter(type=FilterType.ANNOTATION, value = EnableWebMvc.class)})
public class RootConfig {

}

web:

package per.ym.mvcdemo.config;

@Configuration
@EnableWebMvc
@ComponentScan("per.ym.mvcdemo.controller")
public class WebConfig extends WebMvcConfigurerAdapter{
    @Override
    public void configureViewResolvers(ViewResolverRegistry registry) {
        registry.jsp("/WEB-INF/views/", ".jsp");
    }

    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        configurer.enable();
    }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new MyInterceptor()).addPathPatterns("/**");
    }
}

service:

package per.ym.mvcdemo.service;

import org.springframework.stereotype.Service;

@Service
public class HelloService {

    public String hello() {
        return "Hello world.";
    }
}

controller:

package per.ym.mvcdemo.controller;

import per.ym.mvcdemo.service.HelloService;

@RestController
@RequestMapping("/")
public class HelloWorld {

    @Autowired
    private HelloService service;

    public HelloWorld() {
        System.out.println("construct!");
    }

    @RequestMapping("/hello")
    public String sayHello() {
        return service.hello();
    }
}

interceptor:

package per.ym.mvcdemo.interceptor;

public class MyInterceptor implements HandlerInterceptor {
    //目标方法运行之前执行
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {
        return true;
    }

    //目标方法执行正确以后执行
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           ModelAndView modelAndView) throws Exception {
    }

    //页面响应以后执行
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
    }
}

2. 原理解析

2.1. AbstractAnnotationConfigDispatcherServletInitializer剖析

在Servlet 3.0环境中,容器会在类路径中查找实现javax.servlet.ServletContainerInitializer接口的类,如果能发现的话,就会用它来配置Servlet容器。

Spring提供了这个接口的实现,名为SpringServletContainerInitializer,这个类反过来又会查找实现WebApplicationInitializer的类并将配置的任务交给它们来完成。Spring 3.2引入了一个便利的WebApplicationInitializer基础实现,也就是AbstractAnnotationConfigDispatcherServletInitializer。因为我们的
MyWebAppInitializer扩展了AbstractAnnotationConfigDispatcherServletInitializer,当然也就实现了WebApplicationInitializer,因此当部署到Servlet 3.0容器中的时候,容器会自动发现它,并用它来配置Servlet上下文。

尽管它的名字很长,但是AbstractAnnotationConfigDispatcherServletInitializer使用起来很简便。它仅要求我们重写其中的三个方法,其他的方法是否重写则根据你的具体需求而定。

第一个方法是getServletMappings(),它会将一个或多个路径映射到DispatcherServlet上。在本例中,它映射的是“/”,这表示它会是应用的默认Servlet。它会处理进入应用的所有请求。

为了理解其他的两个方法,我们首先要理解DispatcherServlet和一个Servlet监听器,也就是ContextLoaderListene(你是否记得使用web.xml方式配置时也会有它的身影)的关系。

两个应用上下文之间的故事:

当DispatcherServlet启动的时候,它会创建Spring应用上下文,并加载配置文件或配置类中所声明的bean。在MyWebAppInitializer的getServletConfigClasses()方法中,我们要求DispatcherServlet加载应用上下文时,使用定义在WebConfig配置类(使用Java配置)中的bean。但是在Spring Web应用中,通常还会有另外一个应用上下文。另外的这个应用上下文是由ContextLoaderListener创建的。

我们希望DispatcherServlet加载包含Web组件的bean,如控制器、视图解析器以及处理器映射,而ContextLoaderListener要加载应用中的其他bean。这些bean通常是驱动应用后端的中间层和数据层组件。

实际上,AbstractAnnotationConfigDispatcherServletInitializer会同时创建DispatcherServlet和ContextLoaderListener。getServletConfigClasses()方法返回的带有@Configuration注解的类将会用来定义DispatcherServlet应用上下文中的bean,我们暂且把它记为context1。getRootConfigClasses()方法返回的带有@Configuration注解的类将会用来配置ContextLoaderListener创建的应用上下文中的bean,记为context2。那这两个上下文的关系是什么呢?答案是,context1会把context2设置为parent,这样,当context1中的bean需要使用到context2中的bean时就可以在其中直接获取,比如当我们把一个service层的bean注入到controller中时。

在本例中,根配置定义在RootConfig中,DispatcherServlet的配置声明在WebConfig中。稍后我们将会看到这两个类的内容。

需要注意的是,通过AbstractAnnotationConfigDispatcherServletInitializer来配置DispatcherServlet是传统web.xml方式的替代方案。如果你愿意的话,可以同时包含web.xml和AbstractAnnotationConfigDispatcherServletInitializer,但这其实并没有必要。

如果按照这种方式配置DispatcherServlet,而不是使用web.xml的话,那唯一问题在于它只能部署到支持Servlet 3.0的服务器中才能正常工作,如Tomcat 7或更高版本。如果你还没有使用支持Servlet 3.0的服务器,那么在AbstractAnnotationConfigDispatcherServletInitializer子类中配置DispatcherServlet的方法就不适合你了。你别无选择,只能使用web.xml了。

2.2. 源码解析

2.2.1. 查找实现javax.servlet.ServletContainerInitializer接口的类

先看一下tomcat调用栈:

springmvc纯注解配置启动过程原理解析_第1张图片

这个发生在web应用的部署过程,看这个方法名称就是处理servlet容器的初始化相关的东西。我们来看看里面是什么内容:

protected void processServletContainerInitializers() {
            //类路径下查找ServletContainerInitializer的实现类
           detectedScis = loader.load(ServletContainerInitializer.class);
}

我们进入 loader.load(ServletContainerInitializer.class);

public List load(Class serviceType) throws IOException {
        String configFile = SERVICES + serviceType.getName();

                Enumeration resources;
        if (loader == null) {
            resources = ClassLoader.getSystemResources(configFile);
        } else {
            //类路径下查找是否有指定的文件
           resources = loader.getResources(configFile);
        }
        while (resources.hasMoreElements()) {
        //将查找到的文件里的内容读取到containerServicesFound中
         parseConfigFile(containerServicesFound, resources.nextElement());
        }
        //使用反射创建查找到的ServletContainerInitializer的实现类
        return loadServices(serviceType, containerServicesFound);
    }

我们看看configFile和containerServicesFound的内容都是什么

springmvc纯注解配置启动过程原理解析_第2张图片

springmvc纯注解配置启动过程原理解析

正如上述中所示的一样,在我们的spring-web-4.3.20.RELEASE.jar中的确有这个文件,其值也是我们查找到的类

springmvc纯注解配置启动过程原理解析_第3张图片

springmvc纯注解配置启动过程原理解析

找到ServletContainerInitializer的实现类后我们返回到processServletContainerInitializers方法中,看它后续的处理

    protected void processServletContainerInitializers() {

        List detectedScis;
        try {
            WebappServiceLoader loader = new WebappServiceLoader<>(context);
            //类路径下查找ServletContainerInitializer的实现类
            detectedScis = loader.load(ServletContainerInitializer.class);
        } catch (IOException e) {
            log.error(sm.getString(
                    "contextConfig.servletContainerInitializerFail",
                    context.getName()),
                e);
            ok = false;
            return;
        }

        for (ServletContainerInitializer sci : detectedScis) {
            initializerClassMap.put(sci, new HashSet>());

            HandlesTypes ht;
            try {
                //获取类上的HandlesTypes注解
                ht = sci.getClass().getAnnotation(HandlesTypes.class);
            } catch (Exception e) {
                if (log.isDebugEnabled()) {
                    log.info(sm.getString("contextConfig.sci.debug",
                            sci.getClass().getName()),
                            e);
                } else {
                    log.info(sm.getString("contextConfig.sci.info",
                            sci.getClass().getName()));
                }
                continue;
            }
            if (ht == null) {
                continue;
            }
            //拿到注解上的value值
            Class[] types = ht.value();
            if (types == null) {
                continue;
            }

            for (Class type : types) {
                if (type.isAnnotation()) {
                    handlesTypesAnnotations = true;
                } else {
                    handlesTypesNonAnnotations = true;
                }
                Set scis =
                        typeInitializerMap.get(type);
                if (scis == null) {
                    scis = new HashSet<>();
                    //保存HandlesTypes注解上的value值
                    typeInitializerMap.put(type, scis);
                }
                scis.add(sci);
            }
        }
    }

看到这里是不是有点懵,HandlesTypes注解上的value用来干什么?下面,我们来看看它是用来干嘛的。

2.2.2. 查找实现WebApplicationInitializer接口的类

首先,我们看看SpringServletContainerInitializer头上的东西

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
    ......
}

看到这里或许能猜到一些东西了吧,实际上,web容器会根据HandlesTypes注解上的value值在类路径下查找它的实现类,在SpringServletContainerInitializer上该值为WebApplicationInitializer,因此它会去查找WebApplicationInitializer的实现类,而这个实现类在我们的类路径下就有我们自己写的MyWebAppInitializer,因此它最终会找到我们的MyWebAppInitializer,而在后面调用SpringServletContainerInitializer的onStartup方法时,它将作为参数被传进去

2.2.3. WebApplicationInitializer实现类接管工作

我们在SpringServletContainerInitializer的onStartup方法中打上断点,既然springmvc是通过该类配置的,那么它肯定会在某个时候调用其中唯一的方法onStartup。

看看它的调用栈

springmvc纯注解配置启动过程原理解析_第4张图片

在启动standardContext时它会调用所有ServletContainerInitializer的实现类以给应用一个自身配置的机会

我们回到StandardContext.startInternal()中看看

springmvc纯注解配置启动过程原理解析_第5张图片

正如我们前面所看到的一样,还是它们三。进入到SpringServletContainerInitializer的onStartup()方法中

public void onStartup(Set> webAppInitializerClasses, ServletContext servletContext)
            throws ServletException {

            List initializers = new LinkedList();

            if (webAppInitializerClasses != null) {
            for (Class waiClass : webAppInitializerClasses) {
                //不是接口不是抽象的WebApplicationInitializer的子类
                if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
                        WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
                    try {
                        initializers.add((WebApplicationInitializer) waiClass.newInstance());
                    }
                    catch (Throwable ex) {
                        throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
                    }
                }
            }
        }

        servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
        AnnotationAwareOrderComparator.sort(initializers);
        for (WebApplicationInitializer initializer : initializers) {
             //调用WebApplicationInitializer实现类的onStartup方法
            initializer.onStartup(servletContext);
        }

只有我们的MyWebAppInitializer

springmvc纯注解配置启动过程原理解析_第6张图片

看到这里你也就应该明白了2.1中所说的内容

在Servlet 3.0环境中,容器会在类路径中查找实现javax.servlet.ServletContainerInitializer接口的类,如果能发现的话,就会用它来配置Servlet容器。

Spring提供了这个接口的实现,名为SpringServletContainerInitializer,这个类反过来又会查找实现WebApplicationInitializer的类并将配置的任务交给它们来完成。

2.2.4. MyWebAppInitializer开工

进入AbstractDispatcherServletInitializer#onStartup(servletContext)方法

@Override
public void onStartup(ServletContext servletContext) throws ServletException {
    //a.调用父类AbstractContextLoaderInitializer的该方法,用于注册ContextLoaderListener
    super.onStartup(servletContext);
    //b.注册dispatcherServlet
    registerDispatcherServlet(servletContext);
}

a.继续进入父类AbstractContextLoaderInitializer#onStartup(ServletContext servletContext)方法

@Override
public void onStartup(ServletContext servletContext) throws ServletException {
    //注册ContextLoaderListener
    registerContextLoaderListener(servletContext);
}

registerContextLoaderListener(servletContext)方法

protected void registerContextLoaderListener(ServletContext servletContext) {
    //创建spring上下文
    WebApplicationContext rootAppContext = createRootApplicationContext();
    if (rootAppContext != null) {
        ContextLoaderListener listener = new ContextLoaderListener(rootAppContext);
        listener.setContextInitializers(getRootApplicationContextInitializers());
        //将ContextLoaderListener添加到servletContext中,这一步等同在web.xml中配置ContextLoaderListener
        servletContext.addListener(listener);
    }
    else {
        logger.debug("No ContextLoaderListener registered, as " +
                "createRootApplicationContext() did not return an application context");
    }
}

先到createRootApplicationContext()中看看

@Override
protected WebApplicationContext createRootApplicationContext() {
    //获取根上下文配置类,会调用到我们自己的MyWebAppInitializer#getRootConfigClasses(),模板方法设计模式
    Class[] configClasses = getRootConfigClasses();
    if (!ObjectUtils.isEmpty(configClasses)) {
        AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();
        rootAppContext.register(configClasses);
        return rootAppContext;
    }
    else {
        return null;
    }
}

进入MyWebAppInitializer#getRootConfigClasses()

@Override
protected Class[] getRootConfigClasses() {
    //使用我们的RootConfig配置类,这会使得ContextLoaderListener所加载的上下文扫 描"per.ym.mvcdemo.service"
    //包下所有的组件并将其纳入到容器中
    return new Class[] {RootConfig.class};
}

ContextLoaderListener配置完成,重新回到AbstractDispatcherServletInitializer#registerDispatcherServlet(servletContext)方法中

protected void registerDispatcherServlet(ServletContext servletContext) {
    String servletName = getServletName();
    //创建dispaherServlet的spring上下文
    WebApplicationContext servletAppContext = createServletApplicationContext();

    //创建DispatcherServlet并传入servletAppContext,它将在servlet生命周期的init方法中被reFresh
    FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
    dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());

    //将DispatcherServlet加入到servletContext中,加上下面的几步同web.xml中配置DispatcherServlet
    ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
    //设置DispatcherServlet随着该servlet容器启动而启动
    registration.setLoadOnStartup(1);
    //设置DispatcherServlet路径映射,将调用我们MyWebAppInitializer#getServletMappings(),即“/”
    registration.addMapping(getServletMappings());
    registration.setAsyncSupported(isAsyncSupported());

    //获取过滤器,该方法默认为空,可重写它加入我们自己的过滤器
    Filter[] filters = getServletFilters();
    if (!ObjectUtils.isEmpty(filters)) {
        for (Filter filter : filters) {
            registerServletFilter(servletContext, filter);
        }
    }

    //该方法默认也为空,我们可以重写它来对DispatcherServlet进行一些额外配置,比如同MyWebAppInitializer
    //中一样,配置一下用于文件上传的multipart
    customizeRegistration(registration);
}

到 createServletApplicationContext()中看看

    @Override
    protected WebApplicationContext createServletApplicationContext() {
        AnnotationConfigWebApplicationContext servletAppContext = new AnnotationConfigWebApplicationContext();
        //获取dispaherServlet的spring上下文配置类,即MyWebAppInitializer#getServletConfigClasses中的WebConfig
        Class[] configClasses = getServletConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            servletAppContext.register(configClasses);
        }
        return servletAppContext;
    }

到这里,我们的MyWebAppInitializer的主要任务也就完成了,即向servlet容器中添加ContextLoaderListener和DispatcherServlet

2.2.5. ContextLoaderListener创建spring上下文

由于ContextLoaderListener实现了javax.servlet.ServletContextListener接口,因此在servlet容器启动时会调用它的contextInitialized方法。

执行ContextLoaderListener#contextInitialized方法

@Override
public void contextInitialized(ServletContextEvent event) {
    initWebApplicationContext(event.getServletContext());
}

在该方法中打个断点,看看tomcat是在哪里调用它的

springmvc纯注解配置启动过程原理解析_第7张图片

也是在StandardContext#startInternal里,到startInternal中看看

        // Call ServletContainerInitializers
        for (Map.Entry>> entry :
            initializers.entrySet()) {
            try {
                entry.getKey().onStartup(entry.getValue(),
                        getServletContext());
            } catch (ServletException e) {
                log.error(sm.getString("standardContext.sciFail"), e);
                ok = false;
                break;
            }
        }

        // Configure and call application event listeners
        if (ok) {
                            //触发监听器
            if (!listenerStart()) {
                log.error(sm.getString("standardContext.listenerFail"));
                ok = false;
            }
        }

在执行完ServletContainerInitializer相关操作后就立刻执行监听器的相关方法

言归正传,看看ContextLoaderListener#contextInitialized方法

/**
 * Initialize the root web application context.
 */
@Override
public void contextInitialized(ServletContextEvent event) {
    initWebApplicationContext(event.getServletContext());
}

进入父类ContextLoader#initWebApplicationContext方法

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
        if (this.context instanceof ConfigurableWebApplicationContext) {
            //这个cwac就是传入ContextLoaderListener的spring上下文
            ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
            if (!cwac.isActive()) {
                if (cwac.getParent() == null) {
                    // The context instance was injected without an explicit parent ->
                    // determine parent for root web application context, if any.
                    ApplicationContext parent = loadParentContext(servletContext);
                    cwac.setParent(parent);
                }
                //配置并刷新spring上下文
                configureAndRefreshWebApplicationContext(cwac, servletContext);

        return this.context;
    }
}

进入configureAndRefreshWebApplicationContext(cwac, servletContext)

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {

    wac.setServletContext(sc);
    String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
    if (configLocationParam != null) {
        wac.setConfigLocation(configLocationParam);
    }

    // The wac environment's #initPropertySources will be called in any case when the context
    // is refreshed; do it eagerly here to ensure servlet property sources are in place for
    // use in any post-processing or initialization that occurs below prior to #refresh
    ConfigurableEnvironment env = wac.getEnvironment();
    if (env instanceof ConfigurableWebEnvironment) {
        ((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
    }

    customizeContext(sc, wac);
    //刷新spring上下文,这里就进入到spring的节奏里了,我们不在往下了
    wac.refresh();
}

2.2.6. 配置DispatcherServlet

在2.2.4,向ServletContext中添加DispatcherServlet时,我们设置了DispatcherServlet随servlet容器的启动而启动,而servlet启动时会执行它的生命周期方法init,DispatcherServlet的init方法在其父类HttpServletBean中

@Override
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.
    //调用子类中的方法,在FrameworkServlet中
    initServletBean();
}

进入FrameworkServlet#initServletBean()

@Override
protected final void initServletBean() throws ServletException {
    if (this.logger.isInfoEnabled()) {
        this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
    }
    long startTime = System.currentTimeMillis();

    try {
        //初始化spring上下文
        this.webApplicationContext = initWebApplicationContext();
        //该方法默认为空
        initFrameworkServlet();
    }
    catch (ServletException ex) {
        this.logger.error("Context initialization failed", ex);
        throw ex;
    }
    catch (RuntimeException ex) {
        this.logger.error("Context initialization failed", ex);
        throw ex;
    }
}

先到initWebApplicationContext()中看看

    protected WebApplicationContext initWebApplicationContext() {
    //rootContext,这个就是ContextLoaderListener加载的spring上下文
    WebApplicationContext rootContext =
            WebApplicationContextUtils.getWebApplicationContext(getServletContext());
    WebApplicationContext wac = null;

    if (this.webApplicationContext != null) {
        // A context instance was injected at construction time -> use it
        //这个wac就是DispatcherServlet的spring上下文
        wac = this.webApplicationContext;
        if (wac instanceof ConfigurableWebApplicationContext) {
            ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
            if (!cwac.isActive()) {
                if (cwac.getParent() == null) {
                    //设置rootContext为parent,这样当需要注入某个bean时就可以从父上下文中获取
                    cwac.setParent(rootContext);
                }
                //配置并刷新spring上下文
                configureAndRefreshWebApplicationContext(cwac);
            }
        }
    }
    return wac;
}

设置父上下文,刷新当前上下文。到这里,我们整个init方法也就完成了

2.2.7. @EnableWebMvc是干什么的

@Configuration
@EnableWebMvc
@ComponentScan("per.ym.mvcdemo.controller")
public class WebConfig extends WebMvcConfigurerAdapter{

看看这个@EnableWebMvc是什么样子的

//这个是关键,向spring上下文中引入DelegatingWebMvcConfiguration
@Import(DelegatingWebMvcConfiguration.class)
public @interface EnableWebMvc {
}

进入DelegatingWebMvcConfiguration

@Configuration
public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {

        private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();

        @Autowired(required = false)
        public void setConfigurers(List configurers) {
            if (!CollectionUtils.isEmpty(configurers)) {
                this.configurers.addWebMvcConfigurers(configurers);
            }
        }

        @Override
        protected void configurePathMatch(PathMatchConfigurer configurer) {
            this.configurers.configurePathMatch(configurer);
        }

        @Override
        protected void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
            this.configurers.configureContentNegotiation(configurer);
        }

        @Override
        protected void configureAsyncSupport(AsyncSupportConfigurer configurer) {
            this.configurers.configureAsyncSupport(configurer);
        }

        @Override
        protected void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
            this.configurers.configureDefaultServletHandling(configurer);
        }

        @Override
        protected void addFormatters(FormatterRegistry registry) {
            this.configurers.addFormatters(registry);
        }

        @Override
        protected void addInterceptors(InterceptorRegistry registry) {
            this.configurers.addInterceptors(registry);
        }

        @Override
        protected void addResourceHandlers(ResourceHandlerRegistry registry) {
            this.configurers.addResourceHandlers(registry);
        }

        @Override
        protected void addCorsMappings(CorsRegistry registry) {
            this.configurers.addCorsMappings(registry);
        }

        @Override
        protected void addViewControllers(ViewControllerRegistry registry) {
            this.configurers.addViewControllers(registry);
        }

        @Override
        protected void configureViewResolvers(ViewResolverRegistry registry) {
            this.configurers.configureViewResolvers(registry);
        }

        @Override
        protected void addArgumentResolvers(List argumentResolvers) {
            this.configurers.addArgumentResolvers(argumentResolvers);
        }

        @Override
        protected void addReturnValueHandlers(List returnValueHandlers) {
            this.configurers.addReturnValueHandlers(returnValueHandlers);
        }

        @Override
        protected void configureMessageConverters(List> converters) {
            this.configurers.configureMessageConverters(converters);
        }

        @Override
        protected void extendMessageConverters(List> converters) {
            this.configurers.extendMessageConverters(converters);
        }

        @Override
        protected void configureHandlerExceptionResolvers(List exceptionResolvers) {
            this.configurers.configureHandlerExceptionResolvers(exceptionResolvers);
        }

        @Override
        protected void extendHandlerExceptionResolvers(List exceptionResolvers) {
            this.configurers.extendHandlerExceptionResolvers(exceptionResolvers);
        }

        @Override
        protected Validator getValidator() {
            return this.configurers.getValidator();
        }

        @Override
        protected MessageCodesResolver getMessageCodesResolver() {
            return this.configurers.getMessageCodesResolver();
        }

    }

该类中有很多配置方法,而这些配置方法都是调用this.configurers来进行配置的,这个configurers是通过下面这种方式注入进来的,注入的参数的类型是WebMvcConfigurer,这个时候你再看看我们的WebConfig,他继承自WebMvcConfigurerAdapter,而这个WebMvcConfigurerAdapter又实现了WebMvcConfigure。因此,这里会把我们的WebConfig注入进来并加入到this.configurers中,最终配置时就会调用我们WebConfig重写的方法,这也是我们的WebConfig为什么要继承WebMvcConfigurerAdapter并重写父类方法的原因

@Autowired(required = false)
//类型是(List,关键是这个WebMvcConfigurer
public void setConfigurers(List configurers) {
    if (!CollectionUtils.isEmpty(configurers)) {
        this.configurers.addWebMvcConfigurers(configurers);
    }
}

说到这里,那么我们WebConfig中重写的方法是在什么时候被调用的呢,DelegatingWebMvcConfiguration继承自WebMvcConfigurationSupport,在这个类里它会引入很多bean到spring上下文中,包括RequestMappingHandlerMapping、PathMatcher、HandlerMapping、BeanNameUrlHandlerMapping等等,这里我们以RequestMappingHandlerMapping为例,进行说明

@Bean
public RequestMappingHandlerMapping requestMappingHandlerMapping() {
    RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();
    mapping.setOrder(0);
    //看这里,设置拦截器
    mapping.setInterceptors(getInterceptors());
    mapping.setContentNegotiationManager(mvcContentNegotiationManager());
    mapping.setCorsConfigurations(getCorsConfigurations());

    PathMatchConfigurer configurer = getPathMatchConfigurer();

    Boolean useSuffixPatternMatch = configurer.isUseSuffixPatternMatch();
    if (useSuffixPatternMatch != null) {
        mapping.setUseSuffixPatternMatch(useSuffixPatternMatch);
    }
    Boolean useRegisteredSuffixPatternMatch = configurer.isUseRegisteredSuffixPatternMatch();
    if (useRegisteredSuffixPatternMatch != null) {
        mapping.setUseRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch);
    }
    Boolean useTrailingSlashMatch = configurer.isUseTrailingSlashMatch();
    if (useTrailingSlashMatch != null) {
        mapping.setUseTrailingSlashMatch(useTrailingSlashMatch);
    }

    UrlPathHelper pathHelper = configurer.getUrlPathHelper();
    if (pathHelper != null) {
        mapping.setUrlPathHelper(pathHelper);
    }
    PathMatcher pathMatcher = configurer.getPathMatcher();
    if (pathMatcher != null) {
        mapping.setPathMatcher(pathMatcher);
    }

    return mapping;
}

到getInterceptors()方法中看看

    protected final Object[] getInterceptors() {
    if (this.interceptors == null) {
        InterceptorRegistry registry = new InterceptorRegistry();
        //看这个方法
        addInterceptors(registry);
        registry.addInterceptor(new ConversionServiceExposingInterceptor(mvcConversionService()));
        registry.addInterceptor(new ResourceUrlProviderExposingInterceptor(mvcResourceUrlProvider()));
        this.interceptors = registry.getInterceptors();
    }
    return this.interceptors.toArray();
}

子类DelegatingWebMvcConfiguration重写这个addInterceptors(registry)方法

@Override
protected void addInterceptors(InterceptorRegistry registry) {
    this.configurers.addInterceptors(registry);
}

这样,他就会调用的我们WebConfig中的addInterceptors(registry)方法了

@Override
public void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(new MyInterceptor()).addPathPatterns("/**");
}

而我们在WebConfig中重写的其他方法也会在创建WebMvcConfigurationSupport中定义的其他bean时被调用

然后,我们就在这里结束了吧......