SpringMVC执行流程及源码分析
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。
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, WebSocket, SockJS, STOMP Messaging.
- Web Reactive：Spring WebFlux, WebClient, 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
图片来源：三、引用参考资料
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, 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)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, 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);
}
}
}
}
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.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, 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()中的关键代码：
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)方法，
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;
}
注意，handleInternal(request, response, (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
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/
免责声明：
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