SpringMVC流程及源码剖析

前言

学了一遍SpringMVC当前，想着做一个总结，温习一下。温习写上面的总结的时候才发现，其实本人学的并不彻底、牢固、也没有学全，视频跟书本是要联合起来一起，每一位老师的视频可能提到的货色都不统一，也导致也不是很全面，书本上会讲的笔记零碎、全面。同时我本人也是一个初学者，上面总结的可能并不欠缺、正确，心愿看到的大神给我指出，在此非常感谢。

[TOC]

一 、Spring外围模块

1、外围模块

Spring Web MVC （下文简称为 SpringMVC ）是 Spring 提供 Web 利用的框架设计，属于体现层的框架。SpringMVC是Spring框架的一部分。
Spring框架包含大抵六大模块，外围容器（Core Container）、AOP和设施反对、数据拜访及集成、Web、报文发送、Test

图片来源于Spring官网5.0.0.M5：

https://docs.spring.io/spring-framework/docs/5.0.0.M5/spring-framework-reference/html/overview.html#overview-modules

对于Spring5模块图，有2点疑难：

1、不分明为什么在Spring官网上5.0版本当前，Release版（稳定版）的都未找到模块图，然而在M（里程碑版）版找到          了，如果有人在5.0当前的Release版（稳定版）找到，麻烦给我留个言，谢谢。2、在其余博文中看到Spring5模块结构图是这样的：

挺奇怪这个图是哪里来的？（路过的大神请指导）

对于问题2，我在Spring5.2.13.RELEASE GA中，找到了如下所示信息：

拷贝以上信息：

Spring Framework Documentation

Version 5.2.13.RELEASE

What’s New, Upgrade Notes, Supported Versions, and other topics, independent of release cadence, are maintained externally on the project’s Github Wiki.

Overviewhistory, design philosophy, feedback, getting started.
CoreIoC Container, Events, Resources, i18n, Validation, Data Binding, Type Conversion, SpEL, AOP.
TestingMock Objects, TestContext Framework, Spring MVC Test, WebTestClient.
Data AccessTransactions, DAO Support, JDBC, O/R Mapping, XML Marshalling.
Web ServletSpring MVC, WebSocket, SockJS, STOMP Messaging.
Web ReactiveSpring WebFlux, WebClient, WebSocket.
IntegrationRemoting, JMS, JCA, JMX, Email, Tasks, Scheduling, Caching.
LanguagesKotlin, Groovy, Dynamic Languages.

依照以上信息的Web Servlet、Web Reactive曾经是分属于不同的模块了。

  • Web Servlet：Spring MVC, WebSocket, SockJS, STOMP Messaging.
  • Web Reactive：Spring WebFlux, WebClient, WebSocket.

Spring官网文档：https://spring.io/projects/spring-framework#learn/

2、Spring版本命名规定（补充）

下面提到了Spring又不同的版本，在此记录一下各个版本的意义。

形容形式阐明含意
Snapshot快照版尚不稳固，仍处于开发中的版本
Release稳定版性能绝对稳固，能够对外发行，但有工夫限度
GA正式版代表宽泛可用的稳定版（General Availability）
M里程碑版（M是Milestone的意思）具备一些全新的性能或是有意义的版本
RC终测版Release Candidate（最终测试），行将作为正式版公布

二、SpringMVC流程及原理

1、执行流程

SpringMVC执行流程图
<font size=4 color=red>图片起源：三、援用参考资料</font>

1.1、执行流程

  • 01、用户发送出申请到前端控制器(中央处理器)DispatcherServlet进行解决。
  • 02、前端控制器DispatcherServlet收到申请后，调用处理器映射器HandlerMapping。
  • 03、处理器映射器HandlerMapping（处理器映射器）依据request申请的URL等信息查找可能进行解决的Handler，以及相干拦截器interceptor，并结构HandlerExecutionChain执行链，而后将结构好的HandlerExecutionChain执行链对象返回给前端控制器DispatcherServlet。
  • 04、前端控制器DispatcherServlet依据处理器映射器HandlerMapping的
  • 05、处理器适配器HandlerAdapter通过适配调用具体的处理器（Handler/Controller），即业务中本人写的Controller。
  • 06、Controller解决完后返回ModelAndView（springmvc的封装对象，将model和view封装在一起）给处理器适配器HandlerAdapter;
  • 07、处理器适配器HandlerAdapter将Controller执行后果ModelAndView返回给前端控制器DispatcherServlet。
  • 08、前端控制器DispatcherServlet调用视图解析器ViewReslover解决ModelAndView。
  • 09、视图解析器ViewReslover解析后依据逻辑视图名解析成物理视图名即具体的页面地址，生成并返回具体对象View（springmvc封装对象，是一个接口）。
  • 10、前端控制器DispatcherServlet依据对象View进行视图渲染,填充Model。
  • 11、前端控制器DispatcherServlet向用户返回响应

1.2、执行流程阐明：

1.2.1、第02、03阐明

(1) 处理器映射器:springmvc框架中的一种对象，框架把实现了HandlerMapping接口的类都叫做映射器(多个);

(2) 处理器映射器作用:依据申请，从springmvc容器对象中获取处理器对象(MyController controller = ctx.getBean("some")

(3) 框架把找到的处理器对象放到一个叫做处理器执行链(HandlerExecutionChain)的类保留

(4) HandlerExecutionchain:类中保留着
 a：处理器对象(MyController);
 b：我的项目中的所有的拦截器List<HandlerInterceptor>

(5) 办法调用:HandlerExecutionChain mappedHandler - getHandler (processedRequest);

1.2.2、第04阐明

(1) HandlerExecutionChain执行链找到对应的处理器映射器HandlerAdapter。
(2) 处理器适配器：springmvc框架中的对象，须要实现HandlerAdapter接口，
(3) 处理器适配器作用：执行处理器办法(调用MyController.doSome()失去返回值ModelAndView )
(4) 前端控制器中调用适配器:HandlerAdapter ha =getHandlerAdapter (mappedHandler.getHandler());
(5) 执行处理器办法:mv= ha.handle (processedRequest, response, mappedHandler.getHandler());

第08阐明：
(1) 视图解析器：springmvc中的对象，须要实现ViewResoler接口(能够有多个)
(2) 视图解析器作用：组成视图残缺门路，应用前缀，后缀。并创立View对象。
(3) view是一个接口，示意视图的，在框架中jsp,htm1不是string示意，而是应用view和他的实现类示意视图。

InternalResourceview：视图类，示意jsp文件，视图解析器会创立InternalResourceView类对象。 这个对象的外面，有一个属性url-/WEB-INF/view/show.jsp

1.2.2、SpringMVC组件阐明

  • (1). 前端控制器（DispatcherServlet）：接管申请，响应后果，相当于电脑的CPU。
  • (2). 处理器映射器（HandlerMapping）：依据URL去查找处理器．
  • (3). 处理器（Handler）：（须要程序员去写代码解决逻辑的）．
  • (4). 处理器适配器（HandlerAdapter）：会把处理器包装成适配器，这样就能够反对多种类型的处理器，类比笔记本的适配器（适配器模式的利用）．
  • (5). 视图解析器（ViewResovler）：进行视图解析，多返回的字符串，进行解决，能够解析成对应的页面．

1.2.3、SpringMVC具体流程图

综上所述，总结下SpringMVC的具体流程图：


<font size=4 color=red>图片起源：三、援用参考资料</font>

二、源码剖析

以下源码起源jar包：spring-webmvc-5.25.RELEASE.jar

1、初始化

1.1、ApplicationContext

ApplicationContext初始化入口类：ApplicationObjectSupport的setApplicationContext办法，setApplicationContext办法中外围局部就是初始化容器initApplicationContext(context)，子类AbstractDetectingUrlHandlerMapping实现了该办法。
类图：

UML图：

RequestMappingHandlerMapping ,用于注解@Controller,@RequestMapping来定义controller.
初始化时,3个类的大抵分工如下:

  • AbstractHandlerMethodMapping定义整个算法流程;
  • RequestMappingInfoHandlerMapping提供匹配条件RequestMappingInfo的解析解决;
  • RequestMappingHandlerMapping依据@RequestMapping注解生成 RequestMappingInfo,同时提供isHandler实现

2、前端控制器（中央处理器）DistepcherServlet

从下面的流程图能够看到前端控制器（中央处理器）DistepcherServlet是SpringMVC外围，查看DistepcherServlet类的继承状况。
UML图：

从继承关系看出:
DistepcherServlet ---> FrameworkServlet ---> HttpServletBean---> HttpServlet
那就阐明DistepcherServlet 类也是一个Servlet类，那最终外围的办法就是service()办法，即Servlet的外围办法。
那就找service()办法，在DistepcherServlet中没有servic()办法，在父类FrameworkServlet有service()办法，源码如下：
起源：

org.springframework.web.servlet.FrameworkServlet.service(HttpServletRequest request, HttpServletResponse response)

/**     * Override the parent class implementation in order to intercept PATCH requests.     */    @Override    protected void service(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());        if (httpMethod == HttpMethod.PATCH || httpMethod == null) {            processRequest(request, response);        }        else {            super.service(request, response);        }    }

能够看到：

FrameworkServlet.service(HttpServletRequest request, HttpServletResponse response)拿到request申请，判断以后申请是否是PATCH申请，不是的就调用父类的servic()办法，掉用父类中的service办法就是去调用该类中doPost(),doGet()办法，依据不同的申请形式而后走doPost()或者doGet()，调用中以doGet()为例，

FrameworkServlet类的doGet()源码：

/**     * Delegate GET requests to processRequest/doService.     * <p>Will also be invoked by HttpServlet's default implementation of {@code doHead},     * with a {@code NoBodyResponse} that just captures the content length.     * @see #doService     * @see #doHead     */    @Override    protected final void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        processRequest(request, response);    }

doGet()又调用FrameworkServlet类中的processRequest(request, response);

/**     * Process this request, publishing an event regardless of the outcome.     * <p>The actual event handling is performed by the abstract     * {@link #doService} template method.     */    protected final void processRequest(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        long startTime = System.currentTimeMillis();        Throwable failureCause = null;        LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();        LocaleContext localeContext = buildLocaleContext(request);        RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();        ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);        asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());        initContextHolders(request, localeContext, requestAttributes);        try {            doService(request, response);        }        catch (ServletException | IOException ex) {            failureCause = ex;            throw ex;        }        catch (Throwable ex) {            failureCause = ex;            throw new NestedServletException("Request processing failed", ex);        }        finally {            resetContextHolders(request, previousLocaleContext, previousAttributes);            if (requestAttributes != null) {                requestAttributes.requestCompleted();            }            logResult(request, response, failureCause, asyncManager);            publishRequestHandledEvent(request, response, startTime, failureCause);        }    }

processRequest(request, response)办法中最要害的又调用了doService(request, response)；查看FrameworkServlet类中的doService(request, response)，或者是调试跟踪可知，doService(request, response)由子类DispatcherServlet实现。

源码起源：

org.springframework.web.servlet.FrameworkServlet.doService(HttpServletRequest request, HttpServletResponse response)

/**     * Subclasses must implement this method to do the work of request handling,     * receiving a centralized callback for GET, POST, PUT and DELETE.     * <p>The contract is essentially the same as that for the commonly overridden     * {@code doGet} or {@code doPost} methods of HttpServlet.     * <p>This class intercepts calls to ensure that exception handling and     * event publication takes place.     * @param request current HTTP request     * @param response current HTTP response     * @throws Exception in case of any kind of processing failure     * @see javax.servlet.http.HttpServlet#doGet     * @see javax.servlet.http.HttpServlet#doPost     */    protected abstract void doService(HttpServletRequest request, HttpServletResponse response)            throws Exception;

查看DispatcherServlet中的doService(HttpServletRequest request, HttpServletResponse response)办法

/**     * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}     * for the actual dispatching.     */    @Override    protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {        logRequest(request);        // Keep a snapshot of the request attributes in case of an include,        // to be able to restore the original attributes after the include.        Map<String, Object> attributesSnapshot = null;        if (WebUtils.isIncludeRequest(request)) {            attributesSnapshot = new HashMap<>();            Enumeration<?> attrNames = request.getAttributeNames();            while (attrNames.hasMoreElements()) {                String attrName = (String) attrNames.nextElement();                if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {                    attributesSnapshot.put(attrName, request.getAttribute(attrName));                }            }        }        // Make framework objects available to handlers and view objects.        request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());        request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);        request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);        request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());        if (this.flashMapManager != null) {            FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);            if (inputFlashMap != null) {                request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));            }            request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());            request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);        }        try {            doDispatch(request, response);        }        finally {            if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {                // Restore the original attribute snapshot, in case of an include.                if (attributesSnapshot != null) {                    restoreAttributesAfterInclude(request, attributesSnapshot);                }            }        }    }

DispatcherServlet的doService()办法中最终调用doDispatch(request, response)，查看源码如下：
org.springframework.web.servlet.DispatcherServlet.doDispatch()

/**     * Process the actual dispatching to the handler.     * <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 {                // 文件上传相干，判断是不是二进制申请                processedRequest = checkMultipart(request);                multipartRequestParsed = (processedRequest != request);                // 获得解决以后申请的controller,这里也称为hanlder处理器,第一个步骤的意义就在这里体现了.这里并不是间接返回controller,而是返回的HandlerExecutionChain申请处理器链对象,该对象封装了handler和拦截器interceptors.                // Determine handler for the current request.                mappedHandler = getHandler(processedRequest);                // 如果handler为空,则返回404                if (mappedHandler == null) {                    noHandlerFound(processedRequest, response);                    return;                }                //3. 获取解决request的处理器适配器HandlerAdapter                // 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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {                        return;                    }                }                //处理器适配器执行之前，查看拦截器的办法                if (!mappedHandler.applyPreHandle(processedRequest, response)) {                    return;                }                //处理器适配器依据找到，执行handler，返回ModelAndView                // Actually invoke the handler.                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());                if (asyncManager.isConcurrentHandlingStarted()) {                    return;                }                applyDefaultViewName(processedRequest, mv);                mappedHandler.applyPostHandle(processedRequest, response, mv);            }            catch (Exception ex) {                dispatchException = ex;            }            catch (Throwable err) {                // As of 4.3, we're processing Errors thrown from handler methods as well,                // making them available for @ExceptionHandler methods and other scenarios.                dispatchException = new NestedServletException("Handler dispatch failed", err);            }            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);        }        catch (Exception ex) {            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);        }        catch (Throwable err) {            triggerAfterCompletion(processedRequest, response, mappedHandler,                    new NestedServletException("Handler processing failed", err));        }        finally {            if (asyncManager.isConcurrentHandlingStarted()) {                // Instead of postHandle and afterCompletion                if (mappedHandler != null) {                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);                }            }            else {                // Clean up any resources used by a multipart request.                if (multipartRequestParsed) {                    cleanupMultipart(processedRequest);                }            }        }    }

能够看出doDispatch()就是SpringMVC的外围代码了，剖析doDispatch()：

2.1、查找处理器映射器HandlerMapping

首先看下处理器映射器HandlerMapping类图：

doDispatch()要害代码：

HandlerExecutionChain mappedHandler = null;mappedHandler = getHandler(processedRequest);

mappedHandler是一个执行链HandlerExecutionChain 对象，这里封装了handler和拦截器interceptors，getHandler(processedRequest)办法就是从处理器映射器HandlerMapping中找到url和controller的对应关系，并返回给前端控制器DispatchServlet。
查看getHandler(processedRequest);源码：

/**     * 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     */    @Nullable    protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {        if (this.handlerMappings != null) {            for (HandlerMapping mapping : this.handlerMappings) {                HandlerExecutionChain handler = mapping.getHandler(request);                if (handler != null) {                    return handler;                }            }        }        return null;    }

调试代码如下：

从代码调试中能够看到handlerMapping中有三个对象：

this.handlerMappings = {ArrayList@4662}  size = 3 0 = {BeanNameUrlHandlerMapping@4791}  1 = {RequestMappingHandlerMapping@4792}  2 = {RouterFunctionMapping@4793}
  • BeanNameUrlHandlerMapping：初始化时会将urlpath做映射存储（xml）；
  • RequestMappingHandlerMapping：初始化时会将Controller中配置@RequestMapping注解的办法做映射存储（注解）；
  • RouterFunctionMapping：

（这个对象不是太了解）
这也就是为什么要去HandlerMapping找一个Handler了，因为处理器映射器HandlerMapping有不同的实现：

  • 1、xml形式
  • 2、注解形式

接着看getHandler(HttpServletRequest request)办法，先遍历HandlerMappers，查找控制器找到之后就返回执行链HandlerExecutionChain类型的Handler。

能够看到返回的Handler中，拿到的就是咱们本人编码的Controller类，以及拦截器（演示我的项目中未编写，所以调试汇总返回的Handler最初是0 interceptors）
HandlerExecutionChain with [com.bjpowernode.controller.MyController#doSome()] and 0 interceptors

将正在调试的idea关上本人编写的Controller来对照，发现统一：

2.2、依据处理器映射器HandlerMapping返回后果调用处理器适配器HandlerAdapter

doDispatch()外面的要害代码：

HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

源码如下：

/**     * Return the HandlerAdapter for this handler object.     * @param handler the handler object to find an adapter for     * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.     */    protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {        if (this.handlerAdapters != null) {            for (HandlerAdapter adapter : this.handlerAdapters) {                if (adapter.supports(handler)) {                    return adapter;                }            }        }        throw new ServletException("No adapter for handler [" + handler +                "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");    }

为什么还要获取处理器适配器HandlerAdapter：与获取处理器映射器HandlerMapping一样，Spring提供了不通的处理器适配器。
调试如下：


查看DEBUG调试模式中getHandlerAdapter（）办法在中的：
handler、adapter、this.handlerAdapters


以下是拷贝的后果：
handler

handler = {HandlerMethod@4792} "com.bjpowernode.controller.MyController#doSome()" logger = {LogAdapter$JavaUtilLog@4858}  bean = {MyController@4859}  beanFactory = {DefaultListableBeanFactory@4847} "org.springframework.beans.factory.support.DefaultListableBeanFactory@56b5a4c3: defining beans [myController,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,org.springframework.web.servlet.view.InternalResourceViewResolver#0]; root of factory hierarchy" beanType = {Class@3782} "class com.bjpowernode.controller.MyController" method = {Method@4860} "public org.springframework.web.servlet.ModelAndView com.bjpowernode.controller.MyController.doSome()" bridgedMethod = {Method@4860} "public org.springframework.web.servlet.ModelAndView com.bjpowernode.controller.MyController.doSome()" parameters = {MethodParameter[0]@4861}  responseStatus = null responseStatusReason = null resolvedFromHandlerMethod = {HandlerMethod@4863} "com.bjpowernode.controller.MyController#doSome()" interfaceParameterAnnotations = null description = "com.bjpowernode.controller.MyController#doSome()"

adapter

adapter = {RequestMappingHandlerAdapter@4827}  customArgumentResolvers = null argumentResolvers = {HandlerMethodArgumentResolverComposite@4833}  initBinderArgumentResolvers = {HandlerMethodArgumentResolverComposite@4834}  customReturnValueHandlers = null returnValueHandlers = {HandlerMethodReturnValueHandlerComposite@4835}  modelAndViewResolvers = null contentNegotiationManager = {ContentNegotiationManager@4836}  messageConverters = {ArrayList@4837}  size = 4 requestResponseBodyAdvice = {ArrayList@4838}  size = 0 webBindingInitializer = null taskExecutor = {SimpleAsyncTaskExecutor@4839}  asyncRequestTimeout = null callableInterceptors = {CallableProcessingInterceptor[0]@4840}  deferredResultInterceptors = {DeferredResultProcessingInterceptor[0]@4842}  reactiveAdapterRegistry = {ReactiveAdapterRegistry@4844}  ignoreDefaultModelOnRedirect = false cacheSecondsForSessionAttributeHandlers = 0 synchronizeOnSession = false sessionAttributeStore = {DefaultSessionAttributeStore@4845}  parameterNameDiscoverer = {DefaultParameterNameDiscoverer@4846}  beanFactory = {DefaultListableBeanFactory@4847} "org.springframework.beans.factory.support.DefaultListableBeanFactory@56b5a4c3: defining beans [myController,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,org.springframework.web.servlet.view.InternalResourceViewResolver#0]; root of factory hierarchy" sessionAttributesHandlerCache = {ConcurrentHashMap@4848}  size = 0 initBinderCache = {ConcurrentHashMap@4849}  size = 0 initBinderAdviceCache = {LinkedHashMap@4850}  size = 0 modelAttributeCache = {ConcurrentHashMap@4851}  size = 0 modelAttributeAdviceCache = {LinkedHashMap@4852}  size = 0 order = 2147483647 supportedMethods = null allowHeader = "GET,HEAD,POST,PUT,PATCH,DELETE,OPTIONS" requireSession = false cacheControl = null cacheSeconds = -1 varyByRequestHeaders = null useExpiresHeader = false useCacheControlHeader = true useCacheControlNoStore = true alwaysMustRevalidate = false servletContext = {ApplicationContextFacade@4754}  logger = {LogAdapter$JavaUtilLog@4854}  applicationContext = {XmlWebApplicationContext@4665} "WebApplicationContext for namespace 'myweb-servlet', started on Tue Mar 02 23:25:35 CST 2021" messageSourceAccessor = {MessageSourceAccessor@4855}

this.handlerAdapters

this.handlerAdapters = {ArrayList@4658}  size = 4 0 = {HttpRequestHandlerAdapter@4810}  1 = {SimpleControllerHandlerAdapter@4820} //XML形式 2 = {RequestMappingHandlerAdapter@4827} //注解形式 3 = {HandlerFunctionAdapter@4832}

能够看到找到4个处理器适配器。通过DEBUG模式能够看到，此次取到的处理器适配器HandlerAdapter是：RequestMappingHandlerAdapter

ha = {RequestMappingHandlerAdapter@4827}

2.3、查看拦截器Interceptor

doDispatch()中的要害代码：

if (!mappedHandler.applyPreHandle(processedRequest, response)) {                    return;                }org.springframework.web.servlet.HandlerExecutionChain#applyPreHandle

applyPreHandle(processedRequest, response)源码：

/**     * Apply preHandle methods of registered interceptors.     * @return {@code true} if the execution chain should proceed with the     * next interceptor or the handler itself. Else, DispatcherServlet assumes     * that this interceptor has already dealt with the response itself.     */    boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {        HandlerInterceptor[] interceptors = getInterceptors();        if (!ObjectUtils.isEmpty(interceptors)) {            for (int i = 0; i < interceptors.length; i++) {                HandlerInterceptor interceptor = interceptors[i];                if (!interceptor.preHandle(request, response, this.handler)) {                    triggerAfterCompletion(request, response, null);                    return false;                }                this.interceptorIndex = i;            }        }        return true;    }

2.3、处理器适配器HandlerAdapter执行Handler（Controller）返回ModelAndView

doDispatch()中的要害代码：

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

DEBUG模式调试，是跳到了：
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter#handle
源码如下：

/**     * This implementation expects the handler to be an {@link HandlerMethod}.     */    @Override    @Nullable    public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)            throws Exception {        return handleInternal(request, response, (HandlerMethod) handler);    }

再往下看handleInternal(request, response, (HandlerMethod) handler)办法，
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal

@Override    protected ModelAndView handleInternal(HttpServletRequest request,            HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {        ModelAndView mav;        checkRequest(request);        // Execute invokeHandlerMethod in synchronized block if required.        if (this.synchronizeOnSession) {            HttpSession session = request.getSession(false);            if (session != null) {                Object mutex = WebUtils.getSessionMutex(session);                synchronized (mutex) {                    mav = invokeHandlerMethod(request, response, handlerMethod);                }            }            else {                // No HttpSession available -> no mutex necessary                mav = invokeHandlerMethod(request, response, handlerMethod);            }        }        else {            // No synchronization on session demanded at all...            mav = invokeHandlerMethod(request, response, handlerMethod);        }        if (!response.containsHeader(HEADER_CACHE_CONTROL)) {            if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {                applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);            }            else {                prepareResponse(response);            }        }        return mav;    }

留神，handleInternal(request, response, (HandlerMethod) handler)办法的返回值是ModelAndView ，这里就实现了处理器适配器HandlerAdapter执行Handler（Controller）并将后果ModelAndView返回给前端控制器DistepchServlet

2.4、视图解析器ViewResolver

  接上2.3：前端控制器DistepchServlet接管到处理器适配器HandlerAdapter返回的ModelAndView当前，这里分2种状况：

  • (1)、如果ModelAndView外面是逻辑视图

前端控制器DistepchServlet调用视图解析器ViewResolver通过逻辑视图查找真正的视图对象View，并返回给前端控制器DistepchServlet。

  • (2)、如果ModelAndView外面是非逻辑视图：

如：MappingJackson2JsonView（把以后数据转为为JSON数据，并不需要对视图逻辑名称进行转换）

总结一下：
视图解析器ViewResolver接口次要作用是解析前端控制器DispatcherServlet传递的逻辑视图名，并将解析后果的真正的视图对象View传回给前端控制器DispatcherServlet

ViewResolverd的实现类：


ViewResolver的UML:

2.5、视图View

2.5.1、视图对象的作用

  • (1)、将控制器返回的数据处理渲染，最终返回客户端展现给用户，次要就是实现转发或者是重定向的操作.。
  • (2)、为了实现视图模型和具体实现技术的解耦（指的是Spring在org.springframework.web.servlet包中定义的形象View接口），详见2.5.2View接口图。
  • (3)、视图对象View由视图解析器负责实例化。因为视图是无状态（每一次申请都会创立一个新的view对象）的，所以不会有线程平安的问题.

2.5.2、View接口图

2.5.3、View的实现类图

2.5.4、View的UML图

.png)

2.5.5、罕用的View视图类

视图类型简介
URL视图资源图InternalResourceView将JSP或其余资源封装成一个视图。被视图解析器InternalResourceViewResolver默认应用。
JstlViewInternalResourceView的子类。如果JSP中应用了JSTL的国际化标签，就须要应用该视图类。
文档视图AbstractExcelViewExcel文档视图的抽象类。
AbstractPdfViewPDF文档视图的抽象类
报表视图ConfigurableJasperReportsView罕用的JasperReports报表视图
JasperReportsHtmlView
JasperReportsPdfView
JasperReportsXlsView
JSON视图MappingJackson2JsonView将数据通过Jackson框架的ObjectMapper对象，以JSON形式输入

2.6、其余重要的点

2.6.1、DispatcherServlet.properties

DispatcherServlet.properties文件是在SpringMVC架包中：

DispatcherServlet.properties内容：

# Default implementation classes for DispatcherServlet's strategy interfaces.# Used as fallback when no matching beans are found in the DispatcherServlet context.# Not meant to be customized by application developers.org.springframework.web.servlet.LocaleResolver=    org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolverorg.springframework.web.servlet.ThemeResolver=    org.springframework.web.servlet.theme.FixedThemeResolverorg.springframework.web.servlet.HandlerMapping=    org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\    org.springframework.web.servlet.function.support.RouterFunctionMappingorg.springframework.web.servlet.HandlerAdapter=    org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\    org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\    org.springframework.web.servlet.function.support.HandlerFunctionAdapterorg.springframework.web.servlet.HandlerExceptionResolver=    org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\    org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\    org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolverorg.springframework.web.servlet.RequestToViewNameTranslator=    org.springframework.web.servlet.view.DefaultRequestToViewNameTranslatororg.springframework.web.servlet.ViewResolver=    org.springframework.web.servlet.view.InternalResourceViewResolverorg.springframework.web.servlet.FlashMapManager=    org.springframework.web.servlet.support.SessionFlashMapManager

SpringMVC为什么能加载不同处理器映射器HandlerMapping、处理器适配器handlerAdapter，就是因为框架配置了这个DispatcherServlet.properties文件。

三、援用参考资料

1、援用材料

  • SpringMVC流程图援用地址：https://www.iqiyi.com/w_19s2gmyazh.html
  • SpringMVC流程图援用地址2：https://blog.csdn.net/win7system/article/details/90674757
  • View视图作用援用地址：https://blog.csdn.net/qq_43193797/article/details/84928603
  • Spring官网文档：https://spring.io/projects/spring-framework#learn/

    在写此文的时候可能还有少部分是参考了其余材料，然而整顿的时候我曾经找不到原文出处了，如果原文作者看到，请及时分割我，我在文章中加上援用出处，谢谢！

2、参考资料

  • 参考：w3cschool-Spring MVC 4.2.4.RELEASE 中文文档：

    https://www.w3cschool.cn/spring_mvc_documentation_linesh_translation/

  • 参考：https://www.cnblogs.com/leftthen/category/790002.html

免责申明：

 本文中应用的局部图片来自于网络（地址见：三、援用参考资料），如有侵权,请分割博主进行删除。

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