目录
2.关键方法-DispatcherServlet的doDispatch方法
一、rest风格使用及原理
1.rest使用
（1）使用@GetMapping、@PostMapping、@DeleteMapping等等。。
（2）Rest风格支持（使用HTTP请求方式动词来表示对资源的操作）
* 以前：/getUser 获取用户 /deleteUser 删除用户 /editUser 修改用户 /saveUser 保存用户
* 现在： /user GET-获取用户 DELETE-删除用户 PUT-修改用户 POST-保存用户
（3）核心Filter；HiddenHttpMethodFilter
用法： 表单method=post，隐藏域 _method=put
注意：表单提交直接使用method=delete、method=put，是不识别的！表单只能写get、post！
SpringBoot中手动开启
spring:
mvc:
hiddenmethod:
filter:
enabled: true #开启页面表单的Rest功能
原因是：spring自动配置已经配置了，需要手动开启
@Bean
@ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
@ConditionalOnProperty(prefix = "spring.mvc.hiddenmethod.filter", name = "enabled", matchIfMissing = false)
public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
return new OrderedHiddenHttpMethodFilter();
}
（4）扩展：如何把_method 这个名字换成我们自己喜欢的。
//自定义filter
import org.springframework.web.filter.HiddenHttpMethodFilter;
@Bean
public HiddenHttpMethodFilter hiddenHttpMethodFilter(){
HiddenHttpMethodFilter methodFilter = new HiddenHttpMethodFilter();
methodFilter.setMethodParam("_m");
return methodFilter;
}
（5）测试rest风格的表单提交
@RequestMapping(value = "/user",method = RequestMethod.GET)
public String getUser(){
return "GET-张三";
}
@RequestMapping(value = "/user",method = RequestMethod.POST)
public String saveUser(){
return "POST-张三";
}
@RequestMapping(value = "/user",method = RequestMethod.PUT)
public String putUser(){
return "PUT-张三";
}
@RequestMapping(value = "/user",method = RequestMethod.DELETE)
public String deleteUser(){
return "DELETE-张三";
}
测试REST风格；
<form action="/user" method="get">
<input value="REST-GET 提交" type="submit"/>
</form>
<form action="/user" method="post">
<input value="REST-POST 提交" type="submit"/>
</form>
<form action="/user" method="post">
<input name="_method" type="hidden" value="delete"/>
<input name="_m" type="hidden" value="delete"/>
<input value="REST-DELETE 提交" type="submit"/>
</form>
<form action="/user" method="post">
<input name="_method" type="hidden" value="PUT"/>
<input value="REST-PUT 提交" type="submit"/>
</form>
2.rest原理（表单提交）
（1）表单提交会带上_method=PUT
（2）请求过来被HiddenHttpMethodFilter拦截
@Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
HttpServletRequest requestToUse = request;
// 请求是否正常，并且是POST
if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
// 获取到_method的值
String paramValue = request.getParameter(this.methodParam);
if (StringUtils.hasLength(paramValue)) {
// 表单提交的_method的值大小写无所谓。
String method = paramValue.toUpperCase(Locale.ENGLISH);
// 兼容以下请求：PUT.DELETE.PATCH
if (ALLOWED_METHODS.contains(method)) {
// 原生request（post），包装模式requesWrapper重写了getMethod方法，返回的是传入的值。
// 过滤器链放行的时候用wrapper。以后的方法调用getMethod是调用requesWrapper的。
requestToUse = new HttpMethodRequestWrapper(request, method);
}
}
}
filterChain.doFilter(requestToUse, response);
}
3.rest使用（客户端工具如postman）
* 如PostMan直接发送Put、delete等方式请求，无需Filter。
request.getMethod() 就直接获取到的PUT、DELETE。
4.rest优化使用，与上面等同。
// @RequestMapping(value = "/user",method = RequestMethod.GET)
@GetMapping("/user")
public String getUser(){
return "GET-张三";
}
// @RequestMapping(value = "/user",method = RequestMethod.POST)
@PostMapping("/user")
public String saveUser(){
return "POST-张三";
}
// @RequestMapping(value = "/user",method = RequestMethod.PUT)
@PutMapping("/user")
public String putUser(){
return "PUT-张三";
}
@DeleteMapping("/user")
// @RequestMapping(value = "/user",method = RequestMethod.DELETE)
public String deleteUser(){
return "DELETE-张三";
}
二、请求映射原理
1.本质还是继承自原生的HttpServlet
（1）继承关系
（2）.doGet、doPost等请求是在FrameworkServlet实现的
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
@Override
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
@Override
protected final void doPut(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
@Override
protected final void doDelete(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
（3）.doGet最终会调用FrameworkServlet的processRequest方法
processRequest调用FrameworkServlet的doService，FrameworkServlet的doService并没有实现，是一个抽象方法。
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);
}
}
（4）DispatcherServlet有最终的doService实现
@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);
}
RequestPath requestPath = null;
if (this.parseRequestPath && !ServletRequestPathUtils.hasParsedRequestPath(request)) {
requestPath = ServletRequestPathUtils.parseAndCache(request);
}
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);
}
}
if (requestPath != null) {
ServletRequestPathUtils.clearParsedRequestPath(request);
}
}
}
（5）DispatcherServlet有doDispatch方法（关键）
2.关键方法-DispatcherServlet的doDispatch方法
（1）doDispatch方法
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
// 文件上传请求默认是false
boolean multipartRequestParsed = false;
// 请求是否是异步，异步管理器
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
// 检查是否是文件上传请求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request. 找到当前请求使用哪个Handler（Controller的方法）处理
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// 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;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 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);
}
}
}
}
（2）getHandler方法
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// HandlerMapping：处理器映射。/xxx->>xxxx
if (this.handlerMappings != null) {
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
（3）HandlerMapping
WebcomePageHandlerMapping：SpringBoot自动配置欢迎页，访问 /能访问到index.html。
RequestMappingHandlerMapping：保存了所有@RequestMapping 和handler的映射规则。
所有的请求映射都在HandlerMapping中。
请求进来，挨个尝试所有的HandlerMapping看是否有请求信息。
* 如果有就找到这个请求对应的handler
* 如果没有就循环查找下一个 HandlerMapping
3.容器中注册的HandlerMapping
HandlerMapping都是在org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration中注册的
// RequestMappingHandlerMapping用于解析所有标注@RequestMapping的请求
@Bean
@Primary
@Override
public RequestMappingHandlerMapping requestMappingHandlerMapping(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {
// Must be @Primary for MvcUriComponentsBuilder to work
return super.requestMappingHandlerMapping(contentNegotiationManager, conversionService,
resourceUrlProvider);
}
// 用于解析欢迎页的请求
@Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
WelcomePageHandlerMapping welcomePageHandlerMapping = new WelcomePageHandlerMapping(
new TemplateAvailabilityProviders(applicationContext), applicationContext, getWelcomePage(),
this.mvcProperties.getStaticPathPattern());
welcomePageHandlerMapping.setInterceptors(getInterceptors(mvcConversionService, mvcResourceUrlProvider));
welcomePageHandlerMapping.setCorsConfigurations(getCorsConfigurations());
return welcomePageHandlerMapping;
}
4.自定义HandlerMapping
我们自定义的映射处理，也可以自己给容器中放HandlerMapping
（有兴趣可以自行百度学习，此处略）
