SpringMVC源码分析--HandlerMappings

时间 2019-11-06

标签 springmvc 源码分析 handlermappings 栏目 Spring 繁體版

原文原文链接

以前分析过SpringMVC中的DispatcherServlet，分析了SpringMVC处理请求的过程。但忽略了一些DispatcherServlet协助请求处理的组件，例如SpringMVC中的HandlerMapping、HandlerAdapter、ViewResolvers等等。java

HandlerMappings

HandlerMappings在DispathServlet中主要做用是为请求的urlpath匹配对应的Controller，创建一个映射关系，根据请求查找Handler、Interceptor。HandlerMappings将请求传递到HandlerExecutionChain上，HandlerExecutionChain包含了一个可以处理该请求的处理器，还能够包含拦截改请求的拦截器。web

在没有处理器映射相关配置状况下，DispatcherServlet会为你建立一个BeanNameUrlHandlerMapping做为默认映射的配置。在DispatchServlet.properties文件中对于HandlerMapping的默认配置是：spring

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
    org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping

HandlerMapping的配置策略通常分为配置式BeanNameUrlHandlerMapping和注解式DefaultAnnotationHandlerMapping。不过DefaultAnnotationHandlerMapping已经被放弃了，取代它的是RequestMappingHandlerMapping，不知道为啥SpringMVC这个默认配置还没有作修改。设计模式

AbstractHandlerMapping

AbstractHandlerMapping是HandlerMapping的抽象实现，是全部HandlerMapping实现类的父类。并发

AbstractHandlerMapping的做用是是为了初始化Interceptors。AbstractHandlerMapping重写了WebApplicationObjectSupport的initApplicationContext方法。mvc

protected void initApplicationContext() throws BeansException {
        extendInterceptors(this.interceptors);
        detectMappedInterceptors(this.adaptedInterceptors);
        initInterceptors();
    }

extendInterceptors方法，Springmvc并无作出具体实现，这里留下一个拓展，子类能够重写这个模板方法，为子类添加或者修改Interceptors。app
detectMappedInterceptors方法将SpringMVC容器中全部MappedInterceptor类的bean添加到adaptedInterceptors中。ide
最后调用initInterceptors初始化拦截器。遍历interceptors将WebRequestInterceptor和HandlerInterceptor类型的拦截器添加到adaptedInterceptors中。ui

HandlerMapping经过getHandler方法来获取请求的处理器Handler和拦截器Interceptor。在getHandlerExecutionChain方法中将遍历以前初始化的adaptedInterceptors，为当前的请求选择对应的MappedInterceptors和adaptedInterceptors。this

AbstractUrlHandlerMapping

AbstractUrlHandlerMapping继承于AbstractHandlerMapping，它是经过URL来匹配具体的Handler。AbstractUrlHandlerMapping维护一个handlerMap来存储Url和Handler的映射关系。

AbstractUrlHandlerMapping重写了AbstractHandlerMapping类中的getHandlerInternal方法。HandlerMapping经过getHandler方法，就会调用这里的getHandlerInternal方法来获取Handler。getHandlerInternal方法中关键调用lookupHandler方法去获取handler。

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 bestMatch = 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);
            }
            bestMatch = matchingPatterns.get(0);
        }
        if (bestMatch != null) {
            handler = this.handlerMap.get(bestMatch);
            if (handler == null) {
                if (bestMatch.endsWith("/")) {
                    handler = this.handlerMap.get(bestMatch.substring(0, bestMatch.length() - 1));
                }
                if (handler == null) {
                    throw new IllegalStateException(
                            "Could not find handler for best pattern match [" + bestMatch + "]");
                }
            }
            // Bean name or resolved handler?
            if (handler instanceof String) {
                String handlerName = (String) handler;
                handler = getApplicationContext().getBean(handlerName);
            }
            validateHandler(handler, request);
            String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, 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(bestMatch, 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, bestMatch, pathWithinMapping, uriTemplateVariables);
        }

        // No handler found...
        return null;
    }

首先调用lookupHandler方法来获取handler。在lookupHandler方法中，先经过URL在handlerMap查找是否有合适的handler。
若是没有获取到handler，遍历handlerMap利用正则匹配的方法，找到符合要求的handlers(有多是多个)。
正则匹配是采用Ant风格，将会经过排序筛选出一个匹配程度最高的Handler。
最后调用buildPathExposingHandler方法构建一个handler,添加PathExposingHandlerInterceptor和UriTemplateVariablesHandlerInterceptor两个拦截器并返回。

上面介绍获取handler的过程当中，会先从handlerMap查找。下面看一下handlerMap是如何初始化的。AbstractUrlHandlerMapping是经过registerHandler初始化handlerMap的。AbstractUrlHandlerMapping共有两个registerHandler方法。分别是注册多个url到一个handler和注册一个url到一个handler。首先判断handlerMap是否有此handler。若是存在的话，判断是否一致，不一致则抛出异常，若是不存在的话，若是url是/、/*，则，返回root handler、default handler，若是不是将添加到handlerMap中。

SimpleUrlHandlerMapping

SimpleUrlHandlerMapping继承于AbstractUrlHandlerMapping。SimpleUrlHandlerMapping重写了父类AbstractHandlerMapping中的初始化方法initApplicationContext。在initApplicationContext方法中调用registerHandlers方法。

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);
            }
        }
    }

判断是url是否以/开头，若是不是，默认补齐/,确保全部的url都是以/开头，而后依次调用父类的registerHandler方法注册到AbstractUrlHandlerMapping中的handlerMap。

在使用SimpleUrlHandlerMapping时，须要在注册的时候配置其urlmap不然会抛异常。

AbstractDetectingUrlHandlerMapping

AbstractDetectingUrlHandlerMapping类继承于AbstractUrlHandlerMapping类，重写了initApplicationContext方法，在initApplicationContext方法中调用了detectHandlers方法。

protected void detectHandlers() throws BeansException {
        if (logger.isDebugEnabled()) {
            logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
        }
        String[] beanNames = (this.detectHandlersInAncestorContexts ?
                BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
                getApplicationContext().getBeanNamesForType(Object.class));

        // Take any bean name that we can determine URLs for.
        for (String beanName : beanNames) {
            String[] urls = determineUrlsForHandler(beanName);
            if (!ObjectUtils.isEmpty(urls)) {
                // URL paths found: Let's consider it a handler.
                registerHandler(urls, beanName);
            }
            else {
                if (logger.isDebugEnabled()) {
                    logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
                }
            }
        }
    }

获取全部容器的beanNames，遍历全部的beanName，调用determineUrlsForHandler方法解析url，这里的determineUrlsForHandler也是运用了模板方法设计模式，具体的实如今其子类中，若是解析到子类，将注册到父类的handlerMap中。

BeanNameUrlHandlerMapping

BeanNameUrlHandlerMapping类的类图大体以下：

BeanNameUrlHandlerMapping类继承于AbstractDetectingUrlHandlerMapping类。重写了父类中的determineUrlsForHandler方法。

protected String[] determineUrlsForHandler(String beanName) {
        List<String> urls = new ArrayList<String>();
        if (beanName.startsWith("/")) {
            urls.add(beanName);
        }
        String[] aliases = getApplicationContext().getAliases(beanName);
        for (String alias : aliases) {
            if (alias.startsWith("/")) {
                urls.add(alias);
            }
        }
        return StringUtils.toStringArray(urls);
    }

其经过beanName解析Url规则也很简单，判断beanName是否以/开头。

BeanNameUrlHandlerMapping是SpringMVC的默认映射配置。

AbstractHandlerMethodMapping

一般咱们也习惯于用@Controller、@Re questMapping来定义Handler，AbstractHandlerMethodMapping能够将method做为Handler来使用。

AbstractHandlerMethodMapping实现了InitializingBean接口，实现了afterPropertiesSet方法。当容器启动的时候会调用initHandlerMethods注册委托handler中的方法。

public void afterPropertiesSet() {
        initHandlerMethods();
    }
    
    protected void initHandlerMethods() {
        if (logger.isDebugEnabled()) {
            logger.debug("Looking for request mappings in application context: " + getApplicationContext());
        }
        String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
                BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
                getApplicationContext().getBeanNamesForType(Object.class));

        for (String beanName : beanNames) {
            if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
                Class<?> beanType = null;
                try {
                    beanType = getApplicationContext().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);
                    }
                }
                if (beanType != null && isHandler(beanType)) {
                    detectHandlerMethods(beanName);
                }
            }
        }
        handlerMethodsInitialized(getHandlerMethods());
    }

在initHandlerMethods方法中，作了如下工做：

首先经过BeanFactoryUtils扫描应用上下文，获取全部的bean。
遍历全部的beanName，调用isHandler方法判断是目标bean是否包含@Controller或@RequestMapping注解。
对于带有@Controller或@RequestMapping注解的类，调用detectHandlerMethods委托处理,获取全部的method，并调用registerHandlerMethod注册全部的方法。

在detectHandlerMethods方法负责将Handler保存到Map中。

protected void detectHandlerMethods(final Object handler) {
       //  获取handler的类型
        Class<?> handlerType = (handler instanceof String ?
                getApplicationContext().getType((String) handler) : handler.getClass());
        final Class<?> userType = ClassUtils.getUserClass(handlerType);
        
        Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
                new MethodIntrospector.MetadataLookup<T>() {
                    @Override
                    public T inspect(Method 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();
            registerHandlerMethod(handler, invocableMethod, mapping);
        }
    }

selectMethods方法中重写了MetadataLookup中的inspect方法，inspect方法中调用了子类RequestMappingHandlerMapping实现了getMappingForMethod模板方法，用于构建RequestMappingInfo。

public static <T> Map<Method, T> selectMethods(Class<?> targetType, final MetadataLookup<T> metadataLookup) {
        final Map<Method, T> methodMap = new LinkedHashMap<Method, T>();
        Set<Class<?>> handlerTypes = new LinkedHashSet<Class<?>>();
        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);

            ReflectionUtils.doWithMethods(currentHandlerType, new ReflectionUtils.MethodCallback() {
                @Override
                public void doWith(Method 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;
    }

在selectMethods经过反射获取全部的方法，重写了doWith方法，将handler中的method和请求对应的RequestMappingInfo保存到methodMap中。

最终detectHandlerMethods将遍历这个methodMap，调用registerHandlerMethod注册HandlerMethod到MappingRegistry。

在AbstractHandlerMethodMapping类中，有个内部类MappingRegistry，用来存储mapping和 handler methods注册关系，并提供了并发访问方法。

AbstractHandlerMethodMapping经过getHandlerInternal来为一个请求选择对应的handler。

protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
       // 根据request获取对应的urlpath
        String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
        if (logger.isDebugEnabled()) {
            logger.debug("Looking up handler method for path " + lookupPath);
        }
        // 获取读锁
        this.mappingRegistry.acquireReadLock();
        try {
          // 调用lookupHandlerMethod方法获取请求对应的HandlerMethod
            HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
            if (logger.isDebugEnabled()) {
                if (handlerMethod != null) {
                    logger.debug("Returning handler method [" + handlerMethod + "]");
                }
                else {
                    logger.debug("Did not find handler method for [" + lookupPath + "]");
                }
            }
            return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
        }
        finally {
            this.mappingRegistry.releaseReadLock();
        }
    }

lookupHandlerMethod的具体实现以下：

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
        List<Match> matches = new ArrayList<Match>();
        // 经过lookupPath获取全部匹配到的path
        List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
        if (directPathMatches != null) {
           // 将匹配条件添加到matches
            addMatchingMappings(directPathMatches, matches, request);
        }
        if (matches.isEmpty()) {
            // 若是没有匹配条件，将全部的匹配条件都加入matches
            addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
        }

        if (!matches.isEmpty()) {
            Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
            Collections.sort(matches, comparator);
            if (logger.isTraceEnabled()) {
                logger.trace("Found " + matches.size() + " matching mapping(s) for [" +
                        lookupPath + "] : " + matches);
            }
            // 选取排序后的第一个做为最近排序条件
            Match bestMatch = matches.get(0);
            if (matches.size() > 1) {
                if (CorsUtils.isPreFlightRequest(request)) {
                    return PREFLIGHT_AMBIGUOUS_MATCH;
                }
                Match secondBestMatch = matches.get(1);
                // 前两个匹配条件排序同样抛出异常
                if (comparator.compare(bestMatch, secondBestMatch) == 0) {
                    Method m1 = bestMatch.handlerMethod.getMethod();
                    Method m2 = secondBestMatch.handlerMethod.getMethod();
                    throw new IllegalStateException("Ambiguous handler methods mapped for HTTP path '" +
                            request.getRequestURL() + "': {" + m1 + ", " + m2 + "}");
                }
            }
            // 将lookupPath设为请求request的PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE属性
            handleMatch(bestMatch.mapping, lookupPath, request);
            return bestMatch.handlerMethod;
        }
        else {
            return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
        }
    }

整个过程以Match做为载体，Match是个内部类，封装了匹配条件和handlerMethod两个属性，默认的实现是将lookupPath设置为请求的属性。

总结

本文从源码角度上分析了HandlerMapping的各类实现。主要功能是为请求找到合适的handler和interceptors，并组合成HandlerExecutionChain。查找handler的过程经过getHandlerInternal方法实现，每一个子类都其不一样的实现。

全部的HandlerMapping的实现都继承于AbstarctHandlerMapping，AbstarctHandlerMapping主要做用是完成拦截器的初始化工做。而经过AbstarctHandlerMapping又衍生出两个系列，AbstractUrlHandlerMapping和AbstractHandlerMethodMapping。

AbstractUrlHandlerMapping也有不少子类的实现，如SimpleUrlHandlerMapping、AbstractDetectingUrlHandlerMapping。整体来讲，AbstractUrlHandlerMapping须要用到一个保存url和handler的对应关系的map，map的初始化工做由子类实现。不一样的子类会有本身的策略，能够在配置文件中注册，也能够在spring容器中找。

AbstractHandlerMethodMapping系列则一般用于注解的方法，解析包含@Controller或者@RequestMapping注解的类，创建url和method的直接对应关系，这也是目前使用最多的一种方式。