[Java知识库]spring mvc请求映射原理

请求映射原理请求过来首先进入

javax.servlet.http.HttpServlet#doGet()->
org.springframework.web.servlet.FrameworkServlet#doGet()->
org.springframework.web.servlet.FrameworkServlet#processRequest()->
org.springframework.web.servlet.DispatcherServlet#doService()->
org.springframework.web.servlet.DispatcherServlet#doDispatch()->

protected void doDispatch(HttpServletRequest request, HttpServletResponse response)
 throws Exception {
	...

	//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;
	}
    
    //为当前handler找到合适的handler适配器
    HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

	...

	// 真正的调用
	mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

	...
}

RequestMappingHandlerMapping：保存了所有@RequestMapping 和handler的映射规则。

org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal()->

protected ModelAndView handleInternal(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
	...
	
	mav = invokeHandlerMethod(request, response, handlerMethod);
	
	...
}

org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#invokeHandlerMethod()->

protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
	...
	//传参解析器
	if (this.argumentResolvers != null) {
		invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
	}
	//返参处理器
	if (this.returnValueHandlers != null) {
		invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
	}
	
	
	invocableMethod.invokeAndHandle(webRequest, mavContainer);
	
}

org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod#invokeAndHandle()->

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
		Object... providedArgs) throws Exception {

	Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);

    ...
}

org.springframework.web.method.support.InvocableHandlerMethod#invokeForRequest()

public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
		Object... providedArgs) throws Exception {

    //准备目标方法的参数值
	Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);

	...

	return doInvoke(args);
}

?参数解析器HandlerMethodArgumentResolver 是为了确定将要执行的目标方法的每一个参数的值是什么。SpringMVC目标方法能写多少种参数类型，取决于参数解析器。

返回值处理器HandlerMethodReturnValueHandler 是为了封装返回数据的参数类型。

封装handler各参数值的主要逻辑

org.springframework.web.method.support.InvocableHandlerMethod#getMethodArgumentValues()

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		MethodParameter[] parameters = getMethodParameters();
		if (ObjectUtils.isEmpty(parameters)) {
			return EMPTY_ARGS;
		}

		Object[] args = new Object[parameters.length];
		for (int i = 0; i < parameters.length; i++) {
			MethodParameter parameter = parameters[i];
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = findProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
				continue;
			}
			if (!this.resolvers.supportsParameter(parameter)) {
				throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
			}
			try {
				args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
			}
			catch (Exception ex) {
				// Leave stack trace for later, exception may actually be resolved and handled...
				if (logger.isDebugEnabled()) {
					String exMsg = ex.getMessage();
					if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {
						logger.debug(formatArgumentError(parameter, exMsg));
					}
				}
				throw ex;
			}
		}
		return args;
	}