HandlerMapping的作用

HandlerMapping的主要作用是注冊(cè)Handler和獲取Handler延曙。

注冊(cè)Handler

HandleMapping注冊(cè)Handler發(fā)生在SpringMVC容器啟動(dòng)的過程中，在注冊(cè)Handler的同時(shí)也初始化攔截器田度。

BeanNameUrlHandlerMapping類圖

注冊(cè)Handle源碼走讀

//AbstractDetectingUrlHandlerMapping類中initApplicationContext()方法

public void initApplicationContext() throws ApplicationContextException { 
//初始化攔截器
super.initApplicationContext(); 
//注冊(cè)處理器
detectHandlers();
}

//AbstractHandlerMapping類中initApplicationContext()實(shí)現(xiàn)
protected void initApplicationContext() throws BeansException {  
extendInterceptors(this.interceptors);
detectMappedInterceptors(this.mappedInterceptors);  
initInterceptors();
}

//AbstractDetectingUrlHandlerMapping類中detectHandlers()實(shí)現(xiàn)
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");
                }
            }
        }
    }


//BeanNameUrlHandlerMapping類中determineUrlsForHandler()實(shí)現(xiàn)
//獲取以"/"開頭的beanName
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);
    }
//AbstractUrlHandlerMapping類中實(shí)現(xiàn)
protected void registerHandler(String[] urlPaths, String beanName) throws BeansException, IllegalStateException {
        Assert.notNull(urlPaths, "URL path array must not be null");
        for (String urlPath : urlPaths) {
            //注冊(cè)處理器
            registerHandler(urlPath, beanName);
        }
    ｝
//AbstractUrlHandlerMapping類中registerHandler()實(shí)現(xiàn)

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);
            }
        }
        //mappedHandler為保存處理器的map,key值為請(qǐng)求地址(/hello)
        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));
                }
            }
        }
    }

獲取Handler

獲取Handler其實(shí)獲取的是HandlerExecutionChain湾宙，HandlerExecutionChain包括一個(gè)Handler和一組攔截器樟氢。

獲取Handler的時(shí)序圖

獲取Handle源碼走讀

//AbstractHandlerMapping類中g(shù)etHandler()實(shí)現(xiàn)
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);
        }
        //獲取HandlerExecutionChain
        return getHandlerExecutionChain(handler, request);
    }

//AbstractHandlerMapping類中g(shù)etHandlerExecutionChain()實(shí)現(xiàn)
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
        HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
                (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
        //將<bean <property>>配置的攔截器添加到對(duì)應(yīng)的攔截器List中
        chain.addInterceptors(getAdaptedInterceptors());

        String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
        for (MappedInterceptor mappedInterceptor : this.mappedInterceptors) {
            if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
                //<mvc:interceptors>都會(huì)被解析成MappedInterceptor
                chain.addInterceptor(mappedInterceptor.getInterceptor());
            }
        }
        return chain;
    }