SpringMVC源码解读

摘要:

SimpleUrlHandlerMapping只是参与Handler的注册,请求映射时由AbstractUrlHandlerMapping搞定.

初始化时,通过setMappings(Properties mappings)或者setUrlMap(Map<String, ?> urlMap)设置映射关系,然后通过WebApplicationObjectSupport的initApplicationContext调用registerHandlers进行注册.

覆写initApplicationContext方法时,先调用父类实现,然后才调用registerHandlers进行注册.其中最终的注册registerHandler实现是由AbstractUrlHandlerMapping实现的.

父类AbstractHandlerMapping继承了WebApplicationObjectSupport,所以SimpleUrlHandlerMapping可以通过覆写initApplicationContext注册Handler.

注册Handler前,不忘靠AbstractHandlerMapping来初始化拦截器.

// SimpleUrlHandlerMapping

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

initApplicationContext主要是进行拦截器的初始化.

　　extendInterceptors是留给子类用的扩展接口,暂时没有使用

　　detectMappedInterceptors是通过BeanFactoryUtils扫描应用下的全部MappedInterceptor类

　　initInterceptors初始化特定的拦截器,检查MappedInterceptor,在需要时适配adaptor HandlerInterceptor

// AbstractHandlerMapping

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

// AbstractHandlerMapping

    /**
     * Extension hook that subclasses can override to register additional interceptors,
     * given the configured interceptors (see {@link #setInterceptors}).
     * <p>Will be invoked before {@link #initInterceptors()} adapts the specified
     * interceptors into {@link HandlerInterceptor} instances.
     * <p>The default implementation is empty.
     * @param interceptors the configured interceptor List (never {@code null}),
     * allowing to add further interceptors before as well as after the existing
     * interceptors
     */
    protected void extendInterceptors(List<Object> interceptors) {
    }

springmvc中经常使用BeanFactoryUtils扫描应用下的类来进行初始化.

// AbstractHandlerMapping

    /**
     * Detects beans of type {@link MappedInterceptor} and adds them to the list of mapped interceptors.
     * This is done in addition to any {@link MappedInterceptor}s that may have been provided via
     * {@link #setInterceptors(Object[])}. Subclasses can override this method to change that.
     *
     * @param mappedInterceptors an empty list to add MappedInterceptor types to
     */
    protected void detectMappedInterceptors(List<MappedInterceptor> mappedInterceptors) {
        mappedInterceptors.addAll(
                BeanFactoryUtils.beansOfTypeIncludingAncestors(
                        getApplicationContext(),MappedInterceptor.class, true, false).values());
    }

// AbstractHandlerMapping

    /**
     * Initialize the specified interceptors, checking for {@link MappedInterceptor}s and adapting
     * HandlerInterceptors where necessary.
     * @see #setInterceptors
     * @see #adaptInterceptor
     */
    protected void initInterceptors() {
        if (!this.interceptors.isEmpty()) {
            for (int i = 0; i < this.interceptors.size(); i++) {
                Object interceptor = this.interceptors.get(i);
                if (interceptor == null) {
                    throw new IllegalArgumentException("Entry number " + i + " in interceptors array is null");
                }
                if (interceptor instanceof MappedInterceptor) {
                    mappedInterceptors.add((MappedInterceptor) interceptor);
                }
                else {
                    adaptedInterceptors.add(adaptInterceptor(interceptor));
                }
            }
        }
    }

适配HandlerInterceptor和WebRequestHandlerInterceptorAdapter(什么是WebRequestHandlerInterceptorAdapter,晚点再说吧,具体看到时候拦截器部分的分析)

// AbstractHandlerMapping

    /**
     * Adapt the given interceptor object to the HandlerInterceptor interface.
     * <p>Supported interceptor types are HandlerInterceptor and WebRequestInterceptor.
     * Each given WebRequestInterceptor will be wrapped in a WebRequestHandlerInterceptorAdapter.
     * Can be overridden in subclasses.
     * @param interceptor the specified interceptor object
     * @return the interceptor wrapped as HandlerInterceptor
     * @see org.springframework.web.servlet.HandlerInterceptor
     * @see org.springframework.web.context.request.WebRequestInterceptor
     * @see WebRequestHandlerInterceptorAdapter
     */
    protected HandlerInterceptor adaptInterceptor(Object interceptor) {
        if (interceptor instanceof HandlerInterceptor) {
            return (HandlerInterceptor) interceptor;
        }
        else if (interceptor instanceof WebRequestInterceptor) {
            return new WebRequestHandlerInterceptorAdapter((WebRequestInterceptor) interceptor);
        }
        else {
            throw new IllegalArgumentException("Interceptor type not supported: " + interceptor.getClass().getName());
        }
    }

这才到SimpleUrlHandlerMapping干活的地方,迭代urlMap调用AbstractUrlHandlerMapping的registerHandler进行注册

(保障url以"/"开头就不多说了)

// SimpleUrlHandlerMapping

    /**
     * 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);
            }
        }
    }

// AbstractUrlHandlerMapping

/**
     * 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.不是单例同时不是懒加载
        if (!this.lazyInitHandlers && handler instanceof String) {
            String handlerName = (String) handler;
            if (getApplicationContext().isSingleton(handlerName)) {
                resolvedHandler = getApplicationContext().getBean(handlerName);
            }
        }

        Object mappedHandler = this.handlerMap.get(urlPath);// 获取之前已经匹配的Handler
        if (mappedHandler != null) {
            if (mappedHandler != resolvedHandler) {// 如果新匹配得到的跟之前已解析到的handler不一致,则抛异常
                throw new IllegalStateException(
                        "Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
                        "]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
            }
        }
        else {
            if (urlPath.equals("/")) {// 设置rootHandler
                if (logger.isInfoEnabled()) {
                    logger.info("Root mapping to " + getHandlerDescription(handler));
                }
                setRootHandler(resolvedHandler);
            }
            else if (urlPath.equals("/*")) {// 设置默认的defaultHandler
                if (logger.isInfoEnabled()) {
                    logger.info("Default mapping to " + getHandlerDescription(handler));
                }
                setDefaultHandler(resolvedHandler);
            }
            else {// 最后才是普通handler的设置
                this.handlerMap.put(urlPath, resolvedHandler);
                if (logger.isInfoEnabled()) {
                    logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
                }
            }
        }
    }