SpringMVC之HandlerMapping源码剖析

学习一种知识，我喜欢看看源码是怎么进行它们类之间的关系以及方法的调用，是怎么实现的。这样我才感觉踏实。

既然现在谈到HandlerMapping,我们先知道HandlerMapping的作用：HandlerMapping的作用就是解析请求链接，然后根据请求链接找到执行这个请求的类（HandlerMapping所说的handler，也就是我们写的Controller或是Action）。

现在我们来了解HandlerMapping的继承体系图：

至于我们在配置文件中配置的BeanNameUrlHandlerMapping或者是SimpleUrlHandlerMapping，他们的目的是一样的，只是通过请求链接来找handler的方式不一样。

我们再来看看更详细的继承关系：

HandlerMapping的使用主要分为两步：注册和查找。

注册是根据配置文件中的配置将一个字符串和一个Controller类以<key,value>的形式存入到Map中，这个key就是对应的url中的某个字段。

        查找就是HandlerMapping根据url中的的某个字段，在Map中以这个字段为key值对应的Controller类，并将Controller类封装成一个HandlerExecutionChain对象，HandlerExecutionChain中除了有Controller对象外，还有一组拦截器。

现在我简单以SimpleUrlHandlerMapping为例子来分析HandlerMapping是如何根据请求链接找到Controller类的。

1.注册

<!--  SpringMVC中的HandlerMapping配置    配置映射器 -->
    <bean id="" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
    <property name="mappings">
    <props>
    <prop key="/*.do">helloword</prop>
    </props>
    </property>
    </bean>
    <!--配置处理器  -->
    
    <bean id="helloword" class="cn.controller.HelloController">
    <property name="methodNameResolver" ref="nameResolver">
    
    </property>
    </bean>

当我们第一次访问服务器的时候IOC容器会根据配置文件中的红色的部分生成一个Map<String, Object>,这个map里面的值就是{/*.do=/helloworld}。

SimpleUrlHandlerMapping的作用就是获取这个集合，然后根据这个集合里的value找到对应的bean，这样就可以把url中的某个字段和我们写的处理器对应起来。下面是SimpleUrlHandlerMapping中的关键源码

/**
     * Calls the {@link #registerHandlers} method in addition to the
     * superclass's initialization.
     */
    @Override
    public void initApplicationContext() throws BeansException {
        super.initApplicationContext();
        registerHandlers(this.urlMap);
    }

我们来看看HandlerMapping的父类

但是在这个类中没有initApplicationContext（）方法，我们就再来看看AbstractUrlHandlerMapping的父类

的确，在这个类中有了我们想要的initApplicationContext（）方法。

/**
     * Initializes the interceptors.
     * @see #extendInterceptors(java.util.List)
     * @see #initInterceptors()
     */
    @Override
    protected void initApplicationContext() throws BeansException {
        extendInterceptors(this.interceptors);
        detectMappedInterceptors(this.adaptedInterceptors);
        initInterceptors();
    }

这个方法就是初始化SpringMVC容器，并对handler进行注册,urlMap中的值根据上面的配置文件就是{/*.do=/helloWorld}的

现在我们一起来看registerHandlers方法，

/**
     * Register all handlers specified in the URL map for the corresponding paths.
     * @param urlMap Map with URL paths as keys and handler beans or bean names as values
     * @throws BeansException if a handler couldn't be registered
     * @throws IllegalStateException if there is a conflicting handler registered
     */
    protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
        if (urlMap.isEmpty()) {
            logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
        }
        else {
            for (Map.Entry<String, Object> entry : urlMap.entrySet()) {
                String url = entry.getKey();
                Object handler = entry.getValue();
                // Prepend with slash if not already present.
                if (!url.startsWith("/")) {
                    url = "/" + url;
                }
                // Remove whitespace from handler bean name.
                if (handler instanceof String) {
                    handler = ((String) handler).trim();
                }
                registerHandler(url, handler);
            }
        }
    }

主要是对urlMap中的key值进行了一些处理，要是没有“/”的就加上"/",去掉空格等处理。这个方法中的重点是调用了registerHandler(url, handler)这个方法，在这个方法是它的父类AbstractUrlHandlerMapping中的方法。

我们来看看AbstractUrlHandlerMapping中的registerHandler(url, handler)的方法

/**
     * Register the specified handler for the given URL path.
     * @param urlPath the URL the bean should be mapped to
     * @param handler the handler instance or handler bean name String
     * (a bean name will automatically be resolved into the corresponding handler bean)
     * @throws BeansException if the handler couldn't be registered
     * @throws IllegalStateException if there is a conflicting handler registered
     */
    protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
        Assert.notNull(urlPath, "URL path must not be null");
        Assert.notNull(handler, "Handler object must not be null");
        Object resolvedHandler = handler;

        // Eagerly resolve handler if referencing singleton via name.
        if (!this.lazyInitHandlers && handler instanceof String) {
            String handlerName = (String) handler;
            if (getApplicationContext().isSingleton(handlerName)) {
                resolvedHandler = getApplicationContext().getBean(handlerName);
            }
        }

        Object mappedHandler = this.handlerMap.get(urlPath);
        if (mappedHandler != null) {
            if (mappedHandler != resolvedHandler) {
                throw new IllegalStateException(
                        "Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
                        "]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
            }
        }
        else {
            if (urlPath.equals("/")) {
                if (logger.isInfoEnabled()) {
                    logger.info("Root mapping to " + getHandlerDescription(handler));
                }
                setRootHandler(resolvedHandler);
            }
            else if (urlPath.equals("/*")) {
                if (logger.isInfoEnabled()) {
                    logger.info("Default mapping to " + getHandlerDescription(handler));
                }
                setDefaultHandler(resolvedHandler);
            }
            else {
                this.handlerMap.put(urlPath, resolvedHandler);
                if (logger.isInfoEnabled()) {
                    logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
                }
            }
        }

看registerHandler方法红色的部分大家，可以看出是根据SimpleUrlHandlerMapping中的urlMap中的value值在ioc容器中找到对应的bean，并将url的某个字段作为key值，bean作为value存入到AbstractUrlHandlerMapping的urlMap属性中去，这样就达到url的某个字段对应到具体的controller了的目的,当遇到有请求访问服务器的时候，就可以根据url找到具体的controller去执行这个请求了。

 2.查找

  在Dispatcher类中，根据配置文件对handlerMapping进行注册，即对handlerMapping的初始化。

protected void initStrategies(ApplicationContext context) {  
initMultipartResolver(context);  
initLocaleResolver(context);  
initThemeResolver(context);  
initHandlerMappings(context);  
initHandlerAdapters(context);  
initHandlerExceptionResolvers(context);  
initRequestToViewNameTranslator(context);  
initViewResolvers(context);

private void initHandlerMappings(ApplicationContext context) {  
this.handlerMappings = null;  
  
if (this.detectAllHandlerMappings) {  
    // Find all HandlerMappings in the ApplicationContext, including ancestor contexts.  
    Map<String, HandlerMapping> matchingBeans =  
            BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);  
    if (!matchingBeans.isEmpty()) {  
        this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());  
        // We keep HandlerMappings in sorted order.  
        OrderComparator.sort(this.handlerMappings);  
    }  
}  
else {  
    try {  
        HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);  
        this.handlerMappings = Collections.singletonList(hm);  
    }  
    catch (NoSuchBeanDefinitionException ex) {  
        // Ignore, we'll add a default HandlerMapping later.  
    }  
}

于在配置文件中有两种不同类型的handlerMapping,所以从ioc容器中读取出来的handlerMapping有两个，然后将这两个handlerMapping的实例放入Dodispatcher中的handlerMappings属性中。

下面一步就是真正的根据url中的某个字段到已经注册好了的Map<urlString,Controller>中找出执行这个url请求的Controller,用户的请求在被Dispatcher拦截后，会交给Dispatcher的doDispatch执行。在doDispatch方法中主要看红色标记的getHandler方法

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {  
        HttpServletRequest processedRequest = request;  
        HandlerExecutionChain mappedHandler = null;  
        int interceptorIndex = -1;  
  
        try {  
            ModelAndView mv;  
            boolean errorView = false;  
  
            try {  
                processedRequest = checkMultipart(request);  
  
                // Determine handler for the current request.  
                mappedHandler = getHandler(processedRequest, false);  
                if (mappedHandler == null || mappedHandler.getHandler() == null) {  
                    noHandlerFound(processedRequest, response);  
                    return;  
                }  
  
                // Determine handler adapter for the current request.  
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());  
  
                // Process last-modified header, if supported by the handler.  
                String method = request.getMethod();  
                boolean isGet = "GET".equals(method);  
                if (isGet || "HEAD".equals(method)) {  
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());  
                    if (logger.isDebugEnabled()) {  
                        String requestUri = urlPathHelper.getRequestUri(request);  
                        logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);  
                    }  
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {  
                        return;  
                    }  
                }  
  
                // Apply preHandle methods of registered interceptors.  
                HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();  
                if (interceptors != null) {  
                    for (int i = 0; i < interceptors.length; i++) {  
                        HandlerInterceptor interceptor = interceptors[i];  
                        if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {  
                            triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);  
                            return;  
                        }  
                        interceptorIndex = i;  
                    }  
                }  
  
                // Actually invoke the handler.  
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());  
  
                // Do we need view name translation?  
                if (mv != null && !mv.hasView()) {  
                    mv.setViewName(getDefaultViewName(request));  
                }  
  
                // Apply postHandle methods of registered interceptors.  
                if (interceptors != null) {  
                    for (int i = interceptors.length - 1; i >= 0; i--) {  
                        HandlerInterceptor interceptor = interceptors[i];  
                        interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);  
                    }  
                }  
            }  
            catch (ModelAndViewDefiningException ex) {  
                logger.debug("ModelAndViewDefiningException encountered", ex);  
                mv = ex.getModelAndView();  
            }  
            catch (Exception ex) {  
                Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);  
                mv = processHandlerException(processedRequest, response, handler, ex);  
                errorView = (mv != null);  
            }  
  
            // Did the handler return a view to render?  
            if (mv != null && !mv.wasCleared()) {  
                render(mv, processedRequest, response);  
                if (errorView) {  
                    WebUtils.clearErrorRequestAttributes(request);  
                }  
            }  
            else {  
                if (logger.isDebugEnabled()) {  
                    logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +  
                            "': assuming HandlerAdapter completed request handling");  
                }  
            }  
  
            // Trigger after-completion for successful outcome.  
            triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);  
        }

getHandler方法主要会调用已经注册好了的handlerMapping中的getHandler方法

DispatcherServlet中的getHandler方法

/**
     * Return the HandlerExecutionChain for this request.
     * <p>Tries all handler mappings in order.
     * @param request current HTTP request
     * @return the HandlerExecutionChain, or {@code null} if no handler could be found
     */
    protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        for (HandlerMapping hm : this.handlerMappings) {
            if (logger.isTraceEnabled()) {
                logger.trace(
                        "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
            }
            HandlerExecutionChain handler = hm.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
        return null;
    }

现在再来看看HandlerMapping的getHandler方法,可以看到HandlerMapping接口中只有一个getHandler方法

public interface HandlerMapping {

    /**
     * Name of the {@link HttpServletRequest} attribute that contains the path
     * within the handler mapping, in case of a pattern match, or the full
     * relevant URI (typically within the DispatcherServlet's mapping) else.
     * <p>Note: This attribute is not required to be supported by all
     * HandlerMapping implementations. URL-based HandlerMappings will
     * typically support it, but handlers should not necessarily expect
     * this request attribute to be present in all scenarios.
     */
    String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";

    /**
     * Name of the {@link HttpServletRequest} attribute that contains the
     * best matching pattern within the handler mapping.
     * <p>Note: This attribute is not required to be supported by all
     * HandlerMapping implementations. URL-based HandlerMappings will
     * typically support it, but handlers should not necessarily expect
     * this request attribute to be present in all scenarios.
     */
    String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern";

    /**
     * Name of the boolean {@link HttpServletRequest} attribute that indicates
     * whether type-level mappings should be inspected.
     * <p>Note: This attribute is not required to be supported by all
     * HandlerMapping implementations.
     */
    String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping";

    /**
     * Name of the {@link HttpServletRequest} attribute that contains the URI
     * templates map, mapping variable names to values.
     * <p>Note: This attribute is not required to be supported by all
     * HandlerMapping implementations. URL-based HandlerMappings will
     * typically support it, but handlers should not necessarily expect
     * this request attribute to be present in all scenarios.
     */
    String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables";

    /**
     * Name of the {@link HttpServletRequest} attribute that contains a map with
     * URI matrix variables.
     * <p>Note: This attribute is not required to be supported by all
     * HandlerMapping implementations and may also not be present depending on
     * whether the HandlerMapping is configured to keep matrix variable content
     * in the request URI.
     */
    String MATRIX_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".matrixVariables";

    /**
     * Name of the {@link HttpServletRequest} attribute that contains the set of
     * producible MediaTypes applicable to the mapped handler.
     * <p>Note: This attribute is not required to be supported by all
     * HandlerMapping implementations. Handlers should not necessarily expect
     * this request attribute to be present in all scenarios.
     */
    String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes";

    /**
     * Return a handler and any interceptors for this request. The choice may be made
     * on request URL, session state, or any factor the implementing class chooses.
     * <p>The returned HandlerExecutionChain contains a handler Object, rather than
     * even a tag interface, so that handlers are not constrained in any way.
     * For example, a HandlerAdapter could be written to allow another framework's
     * handler objects to be used.
     * <p>Returns {@code null} if no match was found. This is not an error.
     * The DispatcherServlet will query all registered HandlerMapping beans to find
     * a match, and only decide there is an error if none can find a handler.
     * @param request current HTTP request
     * @return a HandlerExecutionChain instance containing handler object and
     * any interceptors, or {@code null} if no mapping found
     * @throws Exception if there is an internal error
     */
    HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;

}

再看看实现了HandlerMapping的AbstractHandlerMapping抽象类,AbstractHandlerMapping中的getHandler方法，这个方法的主要作用是根据url找到controller后，并将controller封装成一个HandlerExecutionChain对象

@Override
    public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        Object handler = getHandlerInternal(request);
        if (handler == null) {
            handler = getDefaultHandler();
        }
        if (handler == null) {
            return null;
        }
        // Bean name or resolved handler?
        if (handler instanceof String) {
            String handlerName = (String) handler;
            handler = getApplicationContext().getBean(handlerName);
        }

        HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
        if (CorsUtils.isCorsRequest(request)) {
            CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
            CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
            CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
            executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
        }
        return executionChain;
    }

AbstractHandlerMapping的getHandlerInternal方法是个抽象方法，由AbstractHandlerMapping的子类AbstractUrlHandlerMapping实现

/**
     * Look up a handler for the given request, returning {@code null} if no
     * specific one is found. This method is called by {@link #getHandler};
     * a {@code null} return value will lead to the default handler, if one is set.
     * <p>On CORS pre-flight requests this method should return a match not for
     * the pre-flight request but for the expected actual request based on the URL
     * path, the HTTP methods from the "Access-Control-Request-Method" header, and
     * the headers from the "Access-Control-Request-Headers" header thus allowing
     * the CORS configuration to be obtained via {@link #getCorsConfigurations},
     * <p>Note: This method may also return a pre-built {@link HandlerExecutionChain},
     * combining a handler object with dynamically determined interceptors.
     * Statically specified interceptors will get merged into such an existing chain.
     * @param request current HTTP request
     * @return the corresponding handler instance, or {@code null} if none found
     * @throws Exception if there is an internal error
     */
    protected abstract Object getHandlerInternal(HttpServletRequest request) throws Exception;

AbstractUrlHandlerMapping实现类里面的getHandlerInternal方法

/**
     * Look up a handler for the URL path of the given request.
     * @param request current HTTP request
     * @return the handler instance, or {@code null} if none found
     */
    @Override
    protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
        String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
        Object handler = lookupHandler(lookupPath, request);
        if (handler == null) {
            // We need to care for the default handler directly, since we need to
            // expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
            Object rawHandler = null;
            if ("/".equals(lookupPath)) {
                rawHandler = getRootHandler();
            }
            if (rawHandler == null) {
                rawHandler = getDefaultHandler();
            }
            if (rawHandler != null) {
                // Bean name or resolved handler?
                if (rawHandler instanceof String) {
                    String handlerName = (String) rawHandler;
                    rawHandler = getApplicationContext().getBean(handlerName);
                }
                validateHandler(rawHandler, request);
                handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
            }
        }
        if (handler != null && logger.isDebugEnabled()) {
            logger.debug("Mapping [" + lookupPath + "] to " + handler);
        }
        else if (handler == null && logger.isTraceEnabled()) {
            logger.trace("No handler mapping found for [" + lookupPath + "]");
        }
        return handler;
    }

getLookupPathForRequest方法主要是截取url中对应controller的那一部分，lookupHandler方法根据截取的url字段找到对应的controller，看到红色的部分就和我们注册handlerMapping的那一步相关了，我们早早的就将url的部分字段所对应的controller放到了AbstractUrlHandlerMapping中的handlerMap属性中了，现在就能根据url找到对应的controller了

/**
     * Look up a handler instance for the given URL path.
     * <p>Supports direct matches, e.g. a registered "/test" matches "/test",
     * and various Ant-style pattern matches, e.g. a registered "/t*" matches
     * both "/test" and "/team". For details, see the AntPathMatcher class.
     * <p>Looks for the most exact pattern, where most exact is defined as
     * the longest path pattern.
     * @param urlPath URL the bean is mapped to
     * @param request current HTTP request (to expose the path within the mapping to)
     * @return the associated handler instance, or {@code null} if not found
     * @see #exposePathWithinMapping
     * @see org.springframework.util.AntPathMatcher
     */
    protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
        // Direct match?
        Object handler = this.handlerMap.get(urlPath);
        if (handler != null) {
            // Bean name or resolved handler?
            if (handler instanceof String) {
                String handlerName = (String) handler;
                handler = getApplicationContext().getBean(handlerName);
            }
            validateHandler(handler, request);
            return buildPathExposingHandler(handler, urlPath, urlPath, null);
        }
        // Pattern match?
        List<String> matchingPatterns = new ArrayList<String>();
        for (String registeredPattern : this.handlerMap.keySet()) {
            if (getPathMatcher().match(registeredPattern, urlPath)) {
                matchingPatterns.add(registeredPattern);
            }
            else if (useTrailingSlashMatch()) {
                if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) {
                    matchingPatterns.add(registeredPattern +"/");
                }
            }
        }
        String bestPatternMatch = null;
        Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
        if (!matchingPatterns.isEmpty()) {
            Collections.sort(matchingPatterns, patternComparator);
            if (logger.isDebugEnabled()) {
                logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
            }
            bestPatternMatch = matchingPatterns.get(0);
        }
        if (bestPatternMatch != null) {
            handler = this.handlerMap.get(bestPatternMatch);
            if (handler == null) {
                Assert.isTrue(bestPatternMatch.endsWith("/"));
                handler = this.handlerMap.get(bestPatternMatch.substring(0, bestPatternMatch.length() - 1));
            }
            // Bean name or resolved handler?
            if (handler instanceof String) {
                String handlerName = (String) handler;
                handler = getApplicationContext().getBean(handlerName);
            }
            validateHandler(handler, request);
            String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath);

            // There might be multiple 'best patterns', let's make sure we have the correct URI template variables
            // for all of them
            Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();
            for (String matchingPattern : matchingPatterns) {
                if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) {
                    Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
                    Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
                    uriTemplateVariables.putAll(decodedVars);
                }
            }
            if (logger.isDebugEnabled()) {
                logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
            }
            return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables);
        }
        // No handler found...
        return null;
    }

到这里算是完了。但是大家可能感觉有点蒙，所以还总结了，方便记忆和理解

就对源码中是如何根据url找到对应的controller进行总结

1.SimpleUrlHandlerMapping根据配置文件中的SimpleUrlHandlerMapping的配置,获得一个map集合,map中存储的是{urlString=beanId}。SimpleUrlHandlerMapping调用父类AbstractUrlHandlerMapping的registerHandler方法。

2.AbstractUrlHandlerMapping的registerHandler方法有SimpleUrlHandlerMapping传入的map中的urlString和beanId，并根据beanId找到对应的bean即controller,将urlString和urlString对应的controller放入AbstractUrlHandlerMapping的handlerMap中。

3.Dispatcher获取IOC容器中已经初始化好的HandlerMapping，再由HandlerMapping调用自己的getHandler方法根据请求返回HandlerExecutionChain对象。AbstractHandlerMapping方法实现了HandlerMapping接口的getHandler方法。AbstractHandlerMapping中的getHandler方法的主要作用是找到controller，并对controller进行封装成HandlerExecutionChain对象，HandlerExecutionChain中除了controller对象外，还有拦截器对象的集合。

4.AbstractHandlerMapping的getHandler方法中又 调用了AbstractHandlerMapping子类的AbstractUrlHandlerMapping getHandlerInternal方法。getHandlerInternal方法就是截取url中对应的controller字段，并以这个字段为key值去AbstractUrlHandlerMapping 的handlerMap中找寻对应的value,即controlle。