SpringMVC流程及源码分析
前言
学了一遍SpringMVC以后，想着做一个总结，复习一下。复习写下面的总结的时候才发现，其实自己学的并不彻底、牢固、也没有学全，视频跟书本是要结合起来一起，每一位老师的视频可能提到的东西都不一致，也导致也不是很全面，书本上会讲的笔记系统、全面。同时我自己也是一个初学者，下面总结的可能并不完善、正确，希望看到的大神给我指出，在此非常感谢。
- SpringMVC流程及源码分析
- 一 、Spring核心模块
- 二、SpringMVC流程及原理
- 二、源码分析
- 三、引用参考资料
一 、Spring核心模块
1、核心模块
Spring Web MVC （下文简称为 SpringMVC ）是 Spring 提供 Web 应用的框架设计，属于表现层的框架。SpringMVC是Spring框架的一部分。
Spring框架包括大致六大模块，核心容器（Core Container）、AOP和设备支持、数据访问及集成、Web、报文发送、Test
图片来源于Spring官网5.0.0.M5：
对于Spring5模块图，有2点疑问：
1、不清楚为什么在Spring官网上5.0版本以后，Release版（稳定版）的都未找到模块图，但是在M（里程碑版）版找到 了，如果有人在5.0以后的Release版（稳定版）找到，麻烦给我留个言，谢谢。
2、在其他博文中看到Spring5模块结构图是这样的：
挺奇怪这个图是哪里来的？（路过的大神请指点）
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.
| Overview | history,design philosophy,Feedback,getting started. |
|---|---|
| Core | IoC Container,Events,Resources,i18n,Validation,Data Binding,Type Conversion,SpEL,AOP. |
| Testing | Mock Objects,TestContext Framework,Spring MVC Test,WebTestClient. |
| Data Access | Transactions,DAO Support,JDBC,O/R Mapping,XML Marshalling. |
| Web Servlet | Spring MVC,WebSocket,SockJS,STOMP Messaging. |
| Web Reactive | Spring WebFlux,WebClient,WebSocket. |
| Integration | Remoting,JMS,JCA,JMX,Email,Tasks,Scheduling,Caching. |
| Languages | Kotlin,Groovy,Dynamic Languages. |
按照以上信息的Web Servlet、Web Reactive已经是分属于不同的模块了。
- Web Servlet：Spring MVC,STOMP Messaging.
- Web Reactive：Spring WebFlux,WebSocket.
Spring官方文档：https://spring.io/projects/spring-framework#learn/
2、Spring版本命名规则（补充）
上面提到了Spring又不同的版本，在此记录一下各个版本的意义。
| 描述方式 | 说明 | 含义 |
|---|---|---|
| Snapshot | 快照版 | 尚不稳定，仍处于开发中的版本 |
| Release | 稳定版 | 功能相对稳定，可以对外发行，但有时间限制 |
| GA | 正式版 | 代表广泛可用的稳定版（General Availability） |
| M | 里程碑版 | （M是Milestone的意思）具有一些全新的功能或是有意义的版本 |
| RC | 终测版 | Release Candidate（最终测试），即将作为正式版发布 |
二、SpringMVC流程及原理
1、执行流程
SpringMVC执行流程图
1.1、执行流程
-
01、用户发送出请求到前端控制器(中央处理器)DispatcherServlet进行处理。
-
02、前端控制器DispatcherServlet收到请求后，调用处理器映射器HandlerMapping。
-
03、处理器映射器HandlerMapping（处理器映射器）根据request请求的URL等信息查找能够进行处理的Handler，以及相关拦截器interceptor，并构造HandlerExecutionChain执行链，然后将构造好的HandlerExecutionChain执行链对象返回给前端控制器DispatcherServlet。
-
04、前端控制器DispatcherServlet根据处理器映射器HandlerMapping的
-
05、处理器适配器HandlerAdapter经过适配调用具体的处理器（Handler/Controller），即业务中自己写的Controller。
-
06、Controller处理完后返回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执行结果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处理ModelAndView。
-
09、视图解析器ViewReslover解析后根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根据对象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、执行流程说明：
1.2.1、第02、03说明
(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:根据请求，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)的类保存
(4) HandlerExecutionchain:类中保存着
a：处理器对象(MyController);
b：项目中的所有的拦截器List
(5) 方法调用:HandlerExecutionChain mappedHandler - getHandler (processedRequest);
1.2.2、第04说明
(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，需要实现HandlerAdapter接口，
(3) 处理器适配器作用：执行处理器方法(调用MyController.doSome()得到返回值ModelAndView )
(4) 前端控制器中调用适配器:HandlerAdapter ha =getHandlerAdapter (mappedHandler.getHandler());
(5) 执行处理器方法:mv= ha.handle (processedRequest,response,mappedHandler.getHandler());
第08说明：
(1) 视图解析器：springmvc中的对象，需要实现ViewResoler接口(可以有多个)
(2) 视图解析器作用：组成视图完整路径，使用前缀，后缀。并创建View对象。
(3) view是一个接口，表示视图的，在框架中jsp,htm1不是string表示，而是使用view和他的实现类表示视图。
InternalResourceview：视图类，表示jsp文件，视图解析器会创建InternalResourceView类对象。 这个对象的里面，有一个属性url-/WEB-INF/view/show.jsp
1.2.2、SpringMVC组件说明
- (1). 前端控制器（DispatcherServlet）：接收请求，响应结果，相当于电脑的cpu。
- (2). 处理器映射器（HandlerMapping）：根据URL去查找处理器．
- (3). 处理器（Handler）：（需要程序员去写代码处理逻辑的）．
- (4). 处理器适配器（HandlerAdapter）：会把处理器包装成适配器，这样就可以支持多种类型的处理器，类比笔记本的适配器（适配器模式的应用）．
- (5). 视图解析器（ViewResovler）：进行视图解析，多返回的字符串，进行处理，可以解析成对应的页面．
1.2.3、SpringMVC详细流程图
综上所述，总结下SpringMVC的详细流程图：
图片来源：三、引用参考资料
二、源码分析
以下源码来源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方法，setApplicationContext方法中核心部分就是初始化容器initApplicationContext(context)，子类AbstractDetectingUrlHandlerMapping实现了该方法。
类图：
UML图：
RequestMappingHandlerMapping,用于注解@Controller,@RequestMapping来定义controller.
初始化时,3个类的大致分工如下:
- AbstractHandlerMethodMapping定义整个算法流程;
- RequestMappingInfoHandlerMapping提供匹配条件RequestMappingInfo的解析处理;
- RequestMappingHandlerMapping根据@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
从上面的流程图可以看到前端控制器（中央处理器）DistepcherServlet是SpringMVC核心，查看DistepcherServlet类的继承情况。
UML图：
从继承关系看出:
DistepcherServlet ---> FrameworkServlet ---> HttpServletBean---> HttpServlet
那就说明DistepcherServlet 类也是一个Servlet类，那最终核心的方法就是service()方法，即Servlet的核心方法。
那就找service()方法，在DistepcherServlet中没有servic()方法，在父类FrameworkServlet有service()方法，源码如下：
来源：
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);
}
}
可以看到：
FrameworkServlet.service(HttpServletRequest request,HttpServletResponse response)拿到request请求，判断当前请求是否是PATCH请求，不是的就调用父类的servic()方法，掉用父类中的service方法就是去调用该类中doPost(),doGet()方法，根据不同的请求方式然后走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,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,IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
LocaleContext prevIoUsLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = buildLocaleContext(request);
RequestAttributes prevIoUsAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = buildRequestAttributes(request,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,failureCause,asyncManager);
publishRequestHandledEvent(request,startTime,failureCause);
}
}
processRequest(request,response)方法中最关键的又调用了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。
源码来源：
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)方法
/**
* 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()方法中最终调用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 {
// 文件上传相关，判断是不是二进制请求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 取得处理当前请求的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.这里并不是直接返回controller,而是返回的HandlerExecutionChain请求处理器链对象,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. 获取处理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，检查拦截器的方法
if (!mappedHandler.applyPreHandle(processedRequest,response)) {
return;
}
//处理器适配器根据找到，执行handler，返回ModelAndView
// Actually invoke the handler.
mv = ha.handle(processedRequest,mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest,mv);
mappedHandler.applyPostHandle(processedRequest,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,mappedHandler,mv,dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest,ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest,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);
}
}
}
}
可以看出doDispatch()就是SpringMVC的核心代码了，分析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()关键代码：
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)方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：
从代码调试中可以看到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注解的方法做映射存储（注解）；
-
RouterFunctionMapping：
（这个对象不是太理解）
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方式
-
2、注解方式
接着看getHandler(HttpServletRequest request)方法，先遍历HandlerMappers，查找控制器找到之后就返回执行链HandlerExecutionChain类型的Handler。
可以看到返回的Handler中，拿到的就是我们自己编码的Controller类，以及拦截器（演示项目中未编写，所以调试汇总返回的Handler最后是0 interceptors）
HandlerExecutionChain with [com.bjpowernode.controller.MyController#doSome()] and 0 interceptors
将正在调试的idea打开自己编写的Controller来对照，发现一致：
2.2、根据处理器映射器HandlerMapping返回结果调用处理器适配器HandlerAdapter
doDispatch()里面的关键代码：
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（）方法在中的：
handler、adapter、this.handlerAdapters
以下是拷贝的结果：
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.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,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方式
2 = {RequestMappingHandlerAdapter@4827} //注解方式
3 = {HandlerFunctionAdapter@4832}
可以看到找到4个处理器适配器。通过DEBUG模式可以看到，此次取到的处理器适配器HandlerAdapter是：RequestMappingHandlerAdapter
ha = {RequestMappingHandlerAdapter@4827}
2.3、检查拦截器Interceptor
doDispatch()中的关键代码：
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,this.handler)) {
triggerAfterCompletion(request,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()中的关键代码：
mv = ha.handle(processedRequest,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,(HandlerMethod) handler);
}
再往下看handleInternal(request,(HandlerMethod) handler)方法，
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal
@Override
protected ModelAndView handleInternal(HttpServletRequest request,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,handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request,handlerMethod);
}
}
else {
// No synchronization on session demanded at all...
mav = invokeHandlerMethod(request,handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response,this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
注意，handleInternal(request,(HandlerMethod) handler)方法的返回值是ModelAndView ，这里就完成了处理器适配器HandlerAdapter执行Handler（Controller）并将结果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接收到处理器适配器HandlerAdapter返回的ModelAndView以后，这里分2种情况：
- (1)、如果ModelAndView里面是逻辑视图
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里面是非逻辑视图：
如：MappingJackson2JsonView（把当前数据转为为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接口主要作用是解析前端控制器DispatcherServlet传递的逻辑视图名，并将解析结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，最终返回客户端展示给用户，主要就是完成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包中定义的抽象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。由于视图是无状态（每一次请求都会创建一个新的view对象）的，所以不会有线程安全的问题.
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、常用的View视图类
| 视图类型 | 简介 | |
| URL视图资源图 | InternalResourceView | 将JSP或其他资源封装成一个视图。被视图解析器InternalResourceViewResolver默认使用。 |
| JstlView | InternalResourceView的子类。如果JSP中使用了JSTL的国际化标签，就需要使用该视图类。 | |
| 文档视图 | AbstractExcelView | Excel文档视图的抽象类。 |
| AbstractPdfView | PDF文档视图的抽象类 | |
| 报表视图 | ConfigurableJasperReportsView | 常用的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方式输出 |
2.6、其他重要的点
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.AcceptHeaderLocaleResolver
org.springframework.web.servlet.ThemeResolver=
org.springframework.web.servlet.theme.FixedThemeResolver
org.springframework.web.servlet.HandlerMapping=
org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
org.springframework.web.servlet.function.support.RouterFunctionMapping
org.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.HandlerFunctionAdapter
org.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.DefaultHandlerExceptionResolver
org.springframework.web.servlet.RequestToViewNameTranslator=
org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
org.springframework.web.servlet.ViewResolver=
org.springframework.web.servlet.view.InternalResourceViewResolver
org.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、引用参考资料
1、引用资料
-
SpringMVC流程图引用地址：https://www.iqiyi.com/w_19s2gmyazh.html
-
SpringMVC流程图引用地址2：https://blog.csdn.net/win7system/article/details/90674757
-
View视图作用引用地址：https://blog.csdn.net/qq_43193797/article/details/84928603
-
Spring官方文档：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他资料，但是整理的时候我已经找不到原文出处了，如果原文作者看到，请及时联系我，我在文章中加上引用出处，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/
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