Spring MVC的工作原理,我们来看看其源码实现

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前言

  开心一刻

    晚上陪老丈人吃饭,无缘无故手机响了,我手贱按了免提……哥们:快出来喝酒!哥几次就有呢!我:今天不行,我现在陪老丈人吃饭呢。哥们:那你抓紧喝,我三杯散酱香型散装酱香型酱香茅台白酒 ,把我岳父放倒了才出来的,你也快点。看着我老丈人的脸,谁能谁能告诉我该缘何回了……

猪一样的队友

遗留间题

  在关于利用maven搭建ssm的博客,另一各自 一起去来探讨下问的最多的间题中,我遗留了有有三个 间题:Spring mvc是几时、何地、如保将Model中的属性绑定到哪个作用域,这里的作用域指的是Servlet的四大作用域;不了解间题背景的还要回过头去看看我的上篇博文。

  明确的解答我会装下 最后,在解答间题日后,我先和另一各自 一起去来捋一捋Spring mvc的工作原理。废话过多说,日后日后刚开始另一各自 神秘的探险之旅!

应用示例

  在讲工作原理日后,另一各自 先看有有三个 简单的spring mvc(ssm)示例,以及实现的效果

  工程代码地址:ssm-web 

  工程内控 与效果如上所示,另一各自 不做过多的探究,另一各自 打起精神往下看本篇的重点

工作原理

  准备 - 资源的加载与初始化

    1、DispatcherServlet 静态初始化

      DispatcherServlet富含如下静态块

static {
        // Load default strategy implementations from properties file.
        // This is currently strictly internal and not meant to be customized
        // by application developers.
        try {
            ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
            defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
        }
        catch (IOException ex) {
            throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
        }
    }

      这里会将DispatcherServlet.properties中的内容读取到DispatcherServlet的属性:private static final Properties defaultStrategies中,DispatcherServlet.properties内容如下

      指定了DispatcherServlet策略接口的默认实现,后续DispatcherServlet初始化策略的过前会用到

    2、interceptor定义的加载

      spring启动过程中会调用InterceptorsBeanDefinitionParser的parse法律法律依据来解蒸发另一各自 自定义的interceptor定义,封装成MappedInterceptor类型的bean定义,并装下 spring容器中;另一各自 还要简单的认为spring容器中由于位于了另一各自 自定义的interceptor的bean定义

    3、DispatcherServlet初始化策略:initStrategies

      DispatcherServlet的继承图如下

      DispatcherServlet是有有三个 Servlet,tomcat启动过程中会调用其init法律法律依据,一串的调用后,会调用DispatcherServlet的initStrategies法律法律依据

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

      实例化步骤1中的默认实现,并填充到DispatcherServlet各个属性值中

    4、DefaultAnnotationHandlerMapping的拦截器初始化

      DispatcherServlet.properties种指定了有有三个 默认的HandlerMapping:BeanNameUrlHandlerMapping、DefaultAnnotationHandlerMapping,这两者的类继承图如下(另一各自 暂时只关注DefaultAnnotationHandlerMapping)

      DefaultAnnotationHandlerMapping间接实现了ApplicationContextAware,没人在DefaultAnnotationHandlerMapping实例初始化过程中,会调用setApplicationContext(ApplicationContext applicationContext)法律法律依据,一串调用后,会来到AbstractUrlHandlerMapping的initApplicationContext()

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

      初始化了DefaultAnnotationHandlerMapping的拦截器:interceptor

    另一各自 来看下具体的初始化过程,看看上方的顺序是是是不是要是 我另一方的臆想?

    还要看了,初始化顺序要是 另一各自 上方说的,就有我另一方的意淫;此时的DefaultAnnotationHandlerMapping富含另一各自 自定义的MyInterceptor。初始化过程另一各自 还要关注的要是 上述哪些地方地方,下面另一各自 一起去看看具体请求的过程

  请求的处理

    请求从servlet的service日后日后刚开始,一路到DispatcherServlet的doDispatch,如下图

    doDispatch

/**
 * Process the actual dispatching to the handler. 将请求埋点到具体的handler,也要是

另一各自

的controller
 * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
 * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
 * to find the first that supports the handler class.
 * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
 * themselves to decide which methods are acceptable.
 * @param request current HTTP request
 * @param response current HTTP response
 * @throws Exception in case of any kind of processing failure
 */
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

    try {
        ModelAndView mv = null;
        Exception dispatchException = null;

        try {
            processedRequest = checkMultipart(request);
            multipartRequestParsed = processedRequest != request;

            // Determine handler for the current request. 决定哪个handler来处理当前的请求
            // mappedHandler是由handler和interceptor集合组成的有有三个

执行链,有点硬例如FilterChain
            mappedHandler = getHandler(processedRequest);
            if (mappedHandler == null || mappedHandler.getHandler() == null) {
                noHandlerFound(processedRequest, response);
                return;
            }

            // Determine handler adapter for the current request. 决定哪个adapter来处理当前的请求
            // handlerMapping是找出适配的handler,而真正回调handler的是adapter
            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;
                }
            }

            // handler的前置处理,也要是

调用适配当前url的interceptor的preHandler法律法律依据
            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            try {
                // Actually invoke the handler. 真正调用handler
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
            }
            finally {
                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }
            }

            applyDefaultViewName(request, mv);
            // handler的后置处理,也要是

调用适配当前url的interceptor的postHandler法律法律依据
            mappedHandler.applyPostHandle(processedRequest, response, mv);
        }
        catch (Exception ex) {
            dispatchException = ex;
        }
        // 处理handler返回的结果,会调用适配当前url的interceptor的afterCompletion法律法律依据
        // 这里会将响应结果返回给请求者
        processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
    }
    catch (Exception ex) {
        triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
    }
    catch (Error err) {
        triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
    }
    finally {
        if (asyncManager.isConcurrentHandlingStarted()) {
            // Instead of postHandle and afterCompletion
            mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            return;
        }
        // Clean up any resources used by a multipart request.
        if (multipartRequestParsed) {
            cleanupMultipart(processedRequest);
        }
    }
}
View Code

      handlerMapping具体如保找到匹配当前url的handler(一般而言要是 另一各自 的controller)、handlerAdapter具体如保回调真正的handler,有兴趣的还要自行去跟下,让你不跟了。另一各自 具体看下processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); 你什儿 与另一各自 最初的间题有关

    processDispatchResult

      还要看了model中的persons会被设置到request的attributes中,否则转发请求到show_person.jsp,转发过程中request作用域的变量仍然有效,过多 show_person.jsp中的jstl标签和el表达式都能不能取到persons变量,最后将show_person.jsp中的内容填充好日后的静态内容返回给请求者;至此就完成了一次请求的响应

间题解答

  回到另一各自 开篇的间题:Spring mvc是几时、何地、如保将Model中的属性绑定到哪个作用域?想必另一各自 由于知道答案了

  Controller中的model、ModelMap的注入由spring mvc完成,你什儿 就有请求传入的参数,用于绑定变量到Servlet作用域;默认状况下,在DispatcherServlet调用了真正的handler日后,将结果返回给请求者的过程中,将model、modelMap中的变量设置到了request的attributes中,转发的过程中,request中的变量仍然有效,过多 show_person.jsp中能取到persons你什儿 变量,自此间题得到解答

总结

  1、Spring MVC工作原理图

    图是用的别人的,具体是谁的我要是 记得了(捂脸)

  2、DefaultAnnotationHandlerMapping在spring3.2中被废弃,替打上去了RequestMappingHandlerMapping