前言
在SpringBoot/SpringMVC中，请求映射是一个很重要的概念。众所周知，应用中实际上只有一个DispatcherServlet处理所有请求，再交由对应的处理器来处理。本文中SpringBoot版本号为2.7.5。
原文地址：https://xuedongyun.cn/post/15349/
请求映射原理
FrameworkServlet
我们知道在SpringMVC中，所有的请求都交由DispatcherServlet统一处理。首先我们看看DispatcherServlet的继承结构
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| HttpServlet
HttpServletBean
FrameworkServlet
DispatcherServlet
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在FrameworkServlet的源码中，我们可以看到，doGet，doPost，doPut，doDelete等底层都是调用的processRequest方法
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| @Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
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processRequest方法核心在于调用了doService方法
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protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
doService(request, response);
}
}
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DispatcherServlet
FrameworkServlet并未实现doService方法，但是DispatcherServlet继承了该类，实现了此方法。doService方法核心在于调用了doDispatch方法
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@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
try {
doDispatch(request, response);
}
}
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doDispatch方法中，会根据请求，找到哪个handler（controller）能处理当前请求。随后使用找到的handler处理请求，获得ModelAndView
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| protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
processedRequest = checkMultipart(request);
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
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可以看到，最为关键的方法为getHandler方法，确定请求具体的handler，我们查看其源码
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| @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;
}
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这里遍历了handlerMappings，调试可以看到，包含五个
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| this.handlerMappings = {ArrayList} size = 5
0 = {RequestMappingHandlerMapping}
1 = {WelcomePageHandlerMapping}
2 = {BeanNameUrlHandlerMapping}
3 = {RouterFunctionMapping}
4 = {SimpleUrlHandlerMapping}
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RequestMappingHandlerMapping保存了所有@RequestMapping注解的请求映射规则。在.mappingRegistry.registry可以看到所有Controller路径都在其中（以及错误路径/error）
WebMvcAutoConfiguration
在WebMvcAutoConfiguration中，SpringBoot为我们注册了所有的HandlerMapping
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@Override
protected RequestMappingHandlerAdapter createRequestMappingHandlerAdapter() {
RequestMappingHandlerMapping mapping = this.mvcRegistrations.getRequestMappingHandlerMapping();
}
@Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
}
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