1、DispatcherServlet的初始化過(guò)程概述

DispatcherServlet是一個(gè)Servlet，也具有Servlet的生命周期：實(shí)例化（instance）->初始化(init)->調(diào)用service方法->銷毀（destroy）兔甘。當(dāng)應(yīng)用啟動(dòng)的時(shí)候绸狐，會(huì)調(diào)用DispatcherServlet的初始化方法卤恳。本篇文章將淺析DispatcherServlet以及兩個(gè)重要組件HandlerMapping和HandlerAdapter的初始化過(guò)程。

DispatcherServlet初始化.jpg

如圖所示：
1寒矿、首先會(huì)從GenericServlet的init()方法開始纬黎，逐步執(zhí)行到DispatcherServlet的父類FrameworkServlet的initServletBean()方法。
2劫窒、在initServletBean()方法中本今，會(huì)去創(chuàng)建IOC容器WebApplicationContext。
3主巍、IOC容器會(huì)去創(chuàng)建組件冠息，這一步中，重點(diǎn)關(guān)注RequestMappingHandlerMapping和RequestMappingHandlerAdapter的初始化孕索。
4逛艰、容器創(chuàng)建完成之后，容器發(fā)布ContextRefreshedEvent事件搞旭。而FrameworkServlet的內(nèi)部類ContextRefreshListener實(shí)現(xiàn)了ApplicationListener散怖，監(jiān)聽到此事件之后菇绵，執(zhí)行onRefresh()方法
5、DispatcherServlet重寫了父類的onRefresh()方法镇眷，并在onRefresh()方法里面咬最，執(zhí)行初始化策略，從而初始化各個(gè)組件欠动。

2永乌、源碼淺析

斷點(diǎn)打到HttpServletBean的init()方法中。

2.1具伍、DispatcherServlet祖?zhèn)鞯膇nit()方法

HttpServletBean的init()方法：

public final void init() throws ServletException {
        // 省略其他代碼
        // 解析init-param并封裝到pvs中翅雏。
        PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
        if (!pvs.isEmpty()) {
            try {
                //將當(dāng)前的servlet類包裝為BeanWrapper，從而注入init-param
                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;
            }
        }
        // 留給子類擴(kuò)展
        initServletBean();
        //省略其他代碼
    }

HttpServletBean的子類FrameworkServlet的initServletBean()方法：

protected final void initServletBean() throws ServletException {
        //省略其他代碼
        long startTime = System.currentTimeMillis();

        try {
            //初始化IOC容器WebApplicationContext
            this.webApplicationContext = initWebApplicationContext();
            //留給子類實(shí)現(xiàn)
            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;
        }
        //省略其他代碼
}

2.2人芽、WebApplicationContext的初始化

接著上一步中FrameworkServlet的 initWebApplicationContext()方法：

protected WebApplicationContext initWebApplicationContext() {
        WebApplicationContext rootContext =
                WebApplicationContextUtils.getWebApplicationContext(getServletContext());
        WebApplicationContext wac = null;

        //省略其他代碼
        if (wac == null) {
            // 創(chuàng)建一個(gè)WebApplicationContext容器
            wac = createWebApplicationContext(rootContext);
        }
        //省略其他代碼
        return wac;
    }

createWebApplicationContext()方法：

protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
        Class<?> contextClass = getContextClass();
        //省略其他代碼
        ConfigurableWebApplicationContext wac =
                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
        //設(shè)置環(huán)境和父容器
        wac.setEnvironment(getEnvironment());
        wac.setParent(parent);
        String configLocation = getContextConfigLocation();
        if (configLocation != null) {
            wac.setConfigLocation(configLocation);
        }
        //初始化Spring環(huán)境包括加載配置文件等
        configureAndRefreshWebApplicationContext(wac);

        return wac;
    }

configureAndRefreshWebApplicationContext(wac)方法：

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
        //省略其他代碼
        // 加載配置文件然后刷新容器
        ConfigurableEnvironment env = wac.getEnvironment();
        if (env instanceof ConfigurableWebEnvironment) {
            ((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
        }

        postProcessWebApplicationContext(wac);
        applyInitializers(wac);
        wac.refresh();
    }

2.3望几、RequestMappingHandlerMapping的初始化

RequestMappingHandlerMapping將會(huì)實(shí)例化，帶有@Controller注解的類中@RequestMapping注解的方法萤厅。SpringMVC也是基于這個(gè)類橄妆，找到請(qǐng)求路徑映射的類和方法。
RequestMappingHandlerMapping初始化過(guò)程如圖所示：

RequestMappingHandlerMapping.jpg

因?yàn)檫@個(gè)類的爺爺類實(shí)現(xiàn)了InitializingBean接口祈坠，而他又重寫了afterPropertiesSet()方法害碾。因此在這個(gè)類初始化的時(shí)候，會(huì)調(diào)用afterPropertiesSet()方法赦拘。
斷點(diǎn)打到RequestMappingHandlerMapping類中的afterPropertiesSet()方法慌随。
afterPropertiesSet方法：

public void afterPropertiesSet() {
        this.config = new RequestMappingInfo.BuilderConfiguration();
        this.config.setUrlPathHelper(getUrlPathHelper());
        this.config.setPathMatcher(getPathMatcher());
        this.config.setSuffixPatternMatch(this.useSuffixPatternMatch);
        this.config.setTrailingSlashMatch(this.useTrailingSlashMatch);
        this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch);
        this.config.setContentNegotiationManager(getContentNegotiationManager());

        super.afterPropertiesSet();
    }

然后來(lái)到爺爺類的afterPropertiesSet方法：

@Override
    public void afterPropertiesSet() {
        initHandlerMethods();
    }

    /**
     * Scan beans in the ApplicationContext, detect and register handler methods.
     * @see #isHandler(Class)
     * @see #getMappingForMethod(Method, Class)
     * @see #handlerMethodsInitialized(Map)
     */
    protected void initHandlerMethods() {
        if (logger.isDebugEnabled()) {
            logger.debug("Looking for request mappings in application context: " + getApplicationContext());
        }
        //這里的beanNames就是IOC容器中所有的組件名稱
        String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
                BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :
                obtainApplicationContext().getBeanNamesForType(Object.class));

        for (String beanName : beanNames) {
            if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
                Class<?> beanType = null;
                try {
                    beanType = obtainApplicationContext().getType(beanName);
                }
                catch (Throwable ex) {
                    // An unresolvable bean type, probably from a lazy bean - let's ignore it.
                    if (logger.isDebugEnabled()) {
                        logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);
                    }
                }
                //判斷這個(gè)類是否帶有@Controller或@RequestMapping注解
                if (beanType != null && isHandler(beanType)) {
                    //檢測(cè)這個(gè)類的方法
                    detectHandlerMethods(beanName);
                }
            }
        }
        handlerMethodsInitialized(getHandlerMethods());
    }

isHandler(beanType)方法：

@Override
    protected boolean isHandler(Class<?> beanType) {
        return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
                AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
    }

detectHandlerMethods(beanName)方法，這里的Handler封裝了類的信息躺同，Method類封裝了方法的信息阁猜，泛型T實(shí)際上是RequestMappingInfo，而RequestMappingInfo封裝了@RequestMapping注解里面各個(gè)屬性的值蹋艺。

protected void detectHandlerMethods(final Object handler) {
        //首先獲取這個(gè)類的Class對(duì)象
        Class<?> handlerType = (handler instanceof String ?
                obtainApplicationContext().getType((String) handler) : handler.getClass());

        if (handlerType != null) {
            final Class<?> userType = ClassUtils.getUserClass(handlerType);
            //查找這個(gè)類的所有方法剃袍，以及創(chuàng)建方法的RequestMappingInfo
            Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
                    (MethodIntrospector.MetadataLookup<T>) method -> {
                        try {
                            return getMappingForMethod(method, userType);
                        }
                        catch (Throwable ex) {
                            throw new IllegalStateException("Invalid mapping on handler class [" +
                                    userType.getName() + "]: " + method, ex);
                        }
                    });
            if (logger.isDebugEnabled()) {
                logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
            }
            for (Map.Entry<Method, T> entry : methods.entrySet()) {
                Method invocableMethod = AopUtils.selectInvocableMethod(entry.getKey(), userType);
                T mapping = entry.getValue();
                //注冊(cè)類、方法以及RequestMappingInfo信息
                registerHandlerMethod(handler, invocableMethod, mapping);
            }
        }
    }

selectMethods()方法：

public static <T> Map<Method, T> selectMethods(Class<?> targetType, final MetadataLookup<T> metadataLookup) {
        //用于返回的Map捎谨，key是方法對(duì)象民效，value是封裝的RequestInfo對(duì)象
        final Map<Method, T> methodMap = new LinkedHashMap<>();
        Set<Class<?>> handlerTypes = new LinkedHashSet<>();
        Class<?> specificHandlerType = null;

        if (!Proxy.isProxyClass(targetType)) {
            handlerTypes.add(targetType);
            specificHandlerType = targetType;
        }
        handlerTypes.addAll(Arrays.asList(targetType.getInterfaces()));

        for (Class<?> currentHandlerType : handlerTypes) {
            final Class<?> targetClass = (specificHandlerType != null ? specificHandlerType : currentHandlerType);
            
            //使用反射處理這個(gè)類的所有方法
            ReflectionUtils.doWithMethods(currentHandlerType, method -> {
                Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);
                T result = metadataLookup.inspect(specificMethod);
                if (result != null) {
                    Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
                    if (bridgedMethod == specificMethod || metadataLookup.inspect(bridgedMethod) == null) {
                        methodMap.put(specificMethod, result);
                    }
                }
            }, ReflectionUtils.USER_DECLARED_METHODS);
        }

        return methodMap;
    }

doWithMethods()方法：

public static void doWithMethods(Class<?> clazz, MethodCallback mc, @Nullable MethodFilter mf) {
        // Keep backing up the inheritance hierarchy.
        Method[] methods = getDeclaredMethods(clazz);
        //遍歷這個(gè)類的所有方法
        for (Method method : methods) {
            if (mf != null && !mf.matches(method)) {
                continue;
            }
            try {
                //執(zhí)行的是上一步中l(wèi)ambda表達(dá)式中的方法
                mc.doWith(method);
            }
            catch (IllegalAccessException ex) {
                throw new IllegalStateException("Not allowed to access method '" + method.getName() + "': " + ex);
            }
        }
        if (clazz.getSuperclass() != null) {
        //然后再遞歸調(diào)用父類的所有方法，這里直接進(jìn)入Object類的所有方法涛救。
            doWithMethods(clazz.getSuperclass(), mc, mf);
        }
        else if (clazz.isInterface()) {
            for (Class<?> superIfc : clazz.getInterfaces()) {
                doWithMethods(superIfc, mc, mf);
            }
        }
    }

mc.doWith(method);

method -> {
                Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);
                //檢查這個(gè)方法畏邢，調(diào)用的是detectHandlerMethods()里面的lambda表達(dá)式中的方法
               //返回的是一個(gè)RequestMappingInfo對(duì)象
                T result = metadataLookup.inspect(specificMethod);
                if (result != null) {
                    Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
                    if (bridgedMethod == specificMethod || metadataLookup.inspect(bridgedMethod) == null) {
                        //將這個(gè)鍵值對(duì)放進(jìn)map里面
                        methodMap.put(specificMethod, result);
                    }
                }
            }

metadataLookup.inspect(specificMethod);

(MethodIntrospector.MetadataLookup<T>) method -> {
                        try {
                            return getMappingForMethod(method, userType);
                        }
                        catch (Throwable ex) {
                            throw new IllegalStateException("Invalid mapping on handler class [" +
                                    userType.getName() + "]: " + method, ex);
                        }
                    }

getMappingForMethod(method, userType)方法：

protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
        //首先創(chuàng)建這個(gè)方法的RequestMappingInfo對(duì)象
        RequestMappingInfo info = createRequestMappingInfo(method);
        if (info != null) {
            //然后創(chuàng)建這個(gè)類的RequestMappingInfo對(duì)象
            RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
            if (typeInfo != null) {
                //將這兩個(gè)RequestMappingInfo對(duì)象合并為一個(gè)對(duì)象，拼接類和方法上的請(qǐng)求路徑等等检吆。
                info = typeInfo.combine(info);
            }
        }
        return info;
    }

typeInfo.combine(info)方法

public RequestMappingInfo combine(RequestMappingInfo other) {
        String name = combineNames(other);
        PatternsRequestCondition patterns = this.patternsCondition.combine(other.patternsCondition);
        RequestMethodsRequestCondition methods = this.methodsCondition.combine(other.methodsCondition);
        ParamsRequestCondition params = this.paramsCondition.combine(other.paramsCondition);
        HeadersRequestCondition headers = this.headersCondition.combine(other.headersCondition);
        ConsumesRequestCondition consumes = this.consumesCondition.combine(other.consumesCondition);
        ProducesRequestCondition produces = this.producesCondition.combine(other.producesCondition);
        RequestConditionHolder custom = this.customConditionHolder.combine(other.customConditionHolder);

        return new RequestMappingInfo(name, patterns,
                methods, params, headers, consumes, produces, custom.getCondition());
    }

重點(diǎn)來(lái)了舒萎，經(jīng)過(guò)上面的步驟，已經(jīng)將需要注冊(cè)的類和方法放到Map<Method, T>中了蹭沛。接下來(lái)臂寝，就是遍歷這個(gè)Map章鲤，然后注冊(cè)Method和RequestMappingInfo了。
在detectHandlerMethods()方法的最后：

for (Map.Entry<Method, T> entry : methods.entrySet()) {
                Method invocableMethod = AopUtils.selectInvocableMethod(entry.getKey(), userType);
                T mapping = entry.getValue();
                registerHandlerMethod(handler, invocableMethod, mapping);
            }

然后進(jìn)入registerHandlerMethod()方法：

public void register(T mapping, Object handler, Method method) {
            //加上寫鎖
            this.readWriteLock.writeLock().lock();
            try {
                //創(chuàng)建HandlerMethod對(duì)象
                //HandlerMethod封裝了類咆贬、方法败徊、方法參數(shù)數(shù)組、這個(gè)類的beanFactory等信息素征。
                HandlerMethod handlerMethod = createHandlerMethod(handler, method);
               //斷言創(chuàng)建出來(lái)的HandlerMethod對(duì)象是唯一的
                assertUniqueMethodMapping(handlerMethod, mapping);

                if (logger.isInfoEnabled()) {
                    logger.info("Mapped \"" + mapping + "\" onto " + handlerMethod);
                }
                //RequestMappingInfo作為鍵集嵌，handlerMethod作為值萝挤，放入mappingLookup中御毅。
                this.mappingLookup.put(mapping, handlerMethod);
                //獲取RequestMappingInfo的請(qǐng)求路徑url
                List<String> directUrls = getDirectUrls(mapping);
                for (String url : directUrls) {
                    //將url作為鍵，RequestMappingInfo作為值怜珍，放入urlLookup中端蛆。
                    this.urlLookup.add(url, mapping);
                }
                //生成一個(gè)名字name
                String name = null;
                if (getNamingStrategy() != null) {
                    name = getNamingStrategy().getName(handlerMethod, mapping);
                    addMappingName(name, handlerMethod);
                }

                CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
                if (corsConfig != null) {
                    this.corsLookup.put(handlerMethod, corsConfig);
                }
                //把以上所有的信息，放進(jìn)registry里面
                this.registry.put(mapping, new MappingRegistration<>(mapping, handlerMethod, directUrls, name));
            }
            finally {
                this.readWriteLock.writeLock().unlock();
            }
        }

DispatcherServlet拿到一個(gè)請(qǐng)求路徑時(shí)酥泛，就是根據(jù)這一步中的幾個(gè)屬性今豆，來(lái)選擇處理這個(gè)請(qǐng)求的類和方法的，到此柔袁，RequestMappingHandlerMapping初始化結(jié)束呆躲。

2.4、RequestMappingHandlerAdapter的初始化

RequestMappingHandlerAdapter實(shí)現(xiàn)了InitializingBean接口捶索，因此會(huì)在初始化時(shí)插掂，調(diào)用afterPropertiesSet()方法：

public void afterPropertiesSet() {
        // 首先初始化ResponseBody增強(qiáng)的bean，賦值給argumentResolvers屬性
        initControllerAdviceCache();
        //初始化各種參數(shù)解析器
        if (this.argumentResolvers == null) {
            List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
            this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        //初始化@initBind參數(shù)解析器腥例，賦值給initBinderArgumentResolvers 屬性
        if (this.initBinderArgumentResolvers == null) {
            List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
            this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        //初始化返回值的解析器辅甥，賦值給returnValueHandlers 屬性
        if (this.returnValueHandlers == null) {
            List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
            this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
        }
    }

2.5、DispatcherServlet的初始化方法

DispatcherServlet的父類FrameworkServlet里面有個(gè)內(nèi)部類ContextRefreshListener燎竖，ContextRefreshListener實(shí)現(xiàn)了ApplicationListener接口璃弄。

private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {

        @Override
        public void onApplicationEvent(ContextRefreshedEvent event) {
            FrameworkServlet.this.onApplicationEvent(event);
        }
    }

IOC容器創(chuàng)建完成以后，會(huì)發(fā)布ContextRefreshedEvent事件构回，ContextRefreshListener監(jiān)聽到此事件以后夏块，進(jìn)入onApplicationEvent()方法：

public void onApplicationEvent(ContextRefreshedEvent event) {
        this.refreshEventReceived = true;
        onRefresh(event.getApplicationContext());
    }

FrameworkServlet的onRefresh()是個(gè)空實(shí)現(xiàn)，而子類DispatcherServlet重寫了這個(gè)方法纤掸，initStrategies()方法內(nèi)部拨扶，實(shí)現(xiàn)了DispatcherServlet的初始化邏輯

@Override
    protected void onRefresh(ApplicationContext context) {
        initStrategies(context);
    }

    /**
     * Initialize the strategy objects that this servlet uses.
     * <p>May be overridden in subclasses in order to initialize further strategy objects.
     */
    protected void initStrategies(ApplicationContext context) {
        //MultipartResolver用于處理文件上傳
        initMultipartResolver(context);
        //Spring的國(guó)際化配置
        initLocaleResolver(context);
        //Web用Theme來(lái)控制網(wǎng)頁(yè)風(fēng)格，一個(gè)主題就是一組靜態(tài)資源
        initThemeResolver(context);
        //客戶端發(fā)出Request時(shí)茁肠，DispatcherServlet將Request提交給HandlerMapping
        //然后HandlerMapping返回響應(yīng)的Controller
        initHandlerMappings(context);
        //HandlerAdapter用于處理Http請(qǐng)求
        initHandlerAdapters(context);
        //異常處理解析器
        initHandlerExceptionResolvers(context);
        //沒有返回視圖名稱的時(shí)候患民，如何確定視圖名稱的組件
        initRequestToViewNameTranslator(context);
        //根據(jù)ModelAndView選擇合適的View進(jìn)行渲染
        initViewResolvers(context);
        //Flash attributes在重定向之前暫存，以便重定向之后還能使用
        //FlashMap用于保持Flash attributes
        initFlashMapManager(context);
    }

其中initHandlerMappings()方法：

private void initHandlerMappings(ApplicationContext context) {
        this.handlerMappings = null;

        if (this.detectAllHandlerMappings) {
            // Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
            //找到ApplicationContext及其父context中的HandlerMappings
            Map<String, HandlerMapping> matchingBeans =
                    BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
            if (!matchingBeans.isEmpty()) {
                //賦值給handlerMappings
                this.handlerMappings = new ArrayList<>(matchingBeans.values());
                // We keep HandlerMappings in sorted order.
                AnnotationAwareOrderComparator.sort(this.handlerMappings);
            }
        }
        //省略其他代碼
    }

DispatcherServlet在選用HandlerMapping的過(guò)程中垦梆，將根據(jù)我們所指定的一系列HandlerMapping的優(yōu)先級(jí)進(jìn)行排序匹颤，然后優(yōu)先使用優(yōu)先級(jí)在前的HandlerMapping仅孩，如果當(dāng)前的HandlerMapping能夠返回可用的Handler，DispatcherServlet則使用當(dāng)前返回的Handler進(jìn)行Web請(qǐng)求的處理印蓖，而不再繼續(xù)詢問(wèn)其他的HandlerMapping辽慕。否則，DispatcherServlet將繼續(xù)按照各個(gè)HandlerMapping的優(yōu)先級(jí)進(jìn)行詢問(wèn)赦肃，直到獲取一個(gè)可用的Handler為止溅蛉。

排序后的handlerMapping如圖，前面分析的RequestMappingHandlerMapping被放在了集合的第一位他宛。

handlerMapping.jpg

initHandlerAdapters()方法：

private void initHandlerAdapters(ApplicationContext context) {
        this.handlerAdapters = null;

        if (this.detectAllHandlerAdapters) {
            // Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
            Map<String, HandlerAdapter> matchingBeans =
                    BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerAdapters = new ArrayList<>(matchingBeans.values());
                // We keep HandlerAdapters in sorted order.
                AnnotationAwareOrderComparator.sort(this.handlerAdapters);
            }
        }
        //省略其他代碼
    }

DispatcherServlet通過(guò)HandlerMapping得到Handler后船侧，會(huì)輪詢HandlerAdapter模塊，查找能夠處理當(dāng)前HTTP請(qǐng)求的HandlerAdapter實(shí)現(xiàn)厅各，HandlerAdapter模塊根據(jù)Handler類型镜撩，來(lái)選擇某個(gè)HandlerAdapter，從而適配當(dāng)前的HTTP請(qǐng)求队塘。
排序后的HandlerAdapter：

Handler Adapter.jpg

同樣前面分析的RequestMappingHandlerAdapter在集合的第一位袁梗。其他的初始化方法與initHandlerMapping和initHandlerAdapter類似，就不再累述了憔古。