Spring接收处理HTTP请求流程浅析
- spring web Http request 请求流程
- 服务器容器监听端口，接收到请求后调用Servlet的service方法。以Tomcat为例，Tomcat监听8080端口（8080为默认配置端口，也可以自行更改），当有请求到达8080端口时，容器将调用Servlet的service方法。javax.servlet.Servlet中定义了所有Servlet必须要实现的方法。在spring web中接收请求的servlet就是DispatcherServlet。
- 在service方法中判断请求类型是GET、POST、PUT......，然后调用相应的doGet()、doPost()、doPut()方法。
- 在doGet/doPost方法中执行processRequest()方法，processRequest()方法执行请求上下文的初始化过程。
- 调用doService()方法，由doService()方法执行doDispatch()方法。
- 最后由doDispatch方法去获取请求的mappedHandler和HandlerAdapter，处理完用户请求之后通过新建一个ServletWebRequest来渲染返回数据。
图片来自网络
如上图中（1）步骤：
请求首先通过ApplicationFilterChain.internalDoFilter(ServletRequest, ServletResponse)方法调用DispatcherServlet的service(ServletRequest, ServletResponse)方法，但是DispatcherServlet中没有此方法，所以调用父类GenericServlet的抽象service(ServletRequest, ServletResponse)方法。最后请求到达HttpServlet.service(ServletRequest, ServletResponse)方法。源码如下
//HttpServlet.service方法的源码
@Override
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException {
HttpServletRequest request;
HttpServletResponse response;
try {
request = (HttpServletRequest) req;
response = (HttpServletResponse) res;
} catch (ClassCastException e) {
throw new ServletException("non-HTTP request or response");
}
service(request, response);
}通过debug源码，service(request,response)调用org.springframework.web.servlet.FrameworkServlet.service(HttpServletRequest, HttpServletResponse)方法。源码如下。
/**
* 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);
}
}FrameworkServlet接收到请求后将请求交个父类HttpServlet.service(HttpServletRequest, HttpServletResponse)处理，此方法中判断请求类型是get、post还是其他请求，更具请求类型调用相应的doGet、doPost方法。源码如下。
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String method = req.getMethod();
if (method.equals(METHOD_GET)) {
long lastModified = getLastModified(req);
if (lastModified == -1) {
// servlet doesn't support if-modified-since, no reason
// to go through further expensive logic
doGet(req, resp);
} else {
long ifModifiedSince;
try {
ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
} catch (IllegalArgumentException iae) {
// Invalid date header - proceed as if none was set
ifModifiedSince = -1;
}
if (ifModifiedSince < (lastModified / 1000 * 1000)) {
// If the servlet mod time is later, call doGet()
// Round down to the nearest second for a proper compare
// A ifModifiedSince of -1 will always be less
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
} else {
resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
}
} else if (method.equals(METHOD_HEAD)) {
long lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
} else if (method.equals(METHOD_POST)) {
doPost(req, resp);
} else if (method.equals(METHOD_PUT)) {
doPut(req, resp);
} else if (method.equals(METHOD_DELETE)) {
doDelete(req, resp);
} else if (method.equals(METHOD_OPTIONS)) {
doOptions(req,resp);
} else if (method.equals(METHOD_TRACE)) {
doTrace(req,resp);
} else {
//
// Note that this means NO servlet supports whatever
// method was requested, anywhere on this server.
//
String errMsg = lStrings.getString("http.method_not_implemented");
Object[] errArgs = new Object[1];
errArgs[0] = method;
errMsg = MessageFormat.format(errMsg, errArgs);
resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
}
}我们以post请求为例，继续debug源码，此时doPost方法执行的是org.springframework.web.servlet.FrameworkServlet.doPost(HttpServletRequest, HttpServletResponse)方法，再由此方法执行org.springframework.web.servlet.FrameworkServlet.processRequest(HttpServletRequest, HttpServletResponse)，最后请求又回到DispatcherServlet.doService(HttpServletRequest, HttpServletResponse)方法，然后委托给DispatcherServlet.doDispatch(HttpServletRequest, HttpServletResponse)处理。到此，流程中步骤（1）结束。
源码如下。
/**
* Process the actual dispatching to the handler.
* 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.
*
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 {
//检查容器中是否同时存在多个不同的请求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 确定当前请求的处理程序
//步骤2、3
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// 为当前请求确定处理程序适配器。步骤4
//这个过程中，会调用MappedInterceptor的matches方法，以此来判断次url是否在拦截范围内
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 (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
//执行拦截器中的preHandle拦截方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 调用实际处理程序。步骤5、6、7
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
//渲染默认的mv。步骤10
applyDefaultViewName(processedRequest, mv);
//执行PostHandle拦截方法
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);
}
//渲染返回值。步骤11。
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);
}
}
}
}
- SpringBoot请求流程方法调用栈
- get请求
debug源码，方法调用如下（出入参解析使用fastjson）：
ApplicationFilterChain.doFilter(ServletRequest, ServletResponse) line: 166
ApplicationFilterChain.internalDoFilter(ServletRequest, ServletResponse) line: 231
//ApplicationFilterChain.internalDoFilter中执行的是DispatcherServlet.service(ServletRequest, ServletResponse)方法，
//但是DispatcherServlet中没有此方法，所以调用父类HttpServlet.service(ServletRequest, ServletResponse)的方法
DispatcherServlet(HttpServlet).service(ServletRequest, ServletResponse)
DispatcherServlet(FrameworkServlet).service(HttpServletRequest, HttpServletResponse)
DispatcherServlet(HttpServlet).service(HttpServletRequest, HttpServletResponse) line: 628
DispatcherServlet(FrameworkServlet).doGet(HttpServletRequest, HttpServletResponse) line: 866
DispatcherServlet(FrameworkServlet).processRequest(HttpServletRequest, HttpServletResponse) line: 959
DispatcherServlet.doService(HttpServletRequest, HttpServletResponse) line: 889
DispatcherServlet.doDispatch(HttpServletRequest, HttpServletResponse) line: 949
RequestMappingHandlerAdapter(AbstractHandlerMethodAdapter).handle(HttpServletRequest, HttpServletResponse, Object) line: 87
RequestMappingHandlerAdapter.handleInternal(HttpServletRequest, HttpServletResponse, HandlerMethod) line: 779
RequestMappingHandlerAdapter.invokeHandlerMethod(HttpServletRequest, HttpServletResponse, HandlerMethod) line: 852
ServletInvocableHandlerMethod.invokeAndHandle(ServletWebRequest, ModelAndViewContainer, Object...) line: 102
//解析传入参数、调用方法、返回结果
ServletInvocableHandlerMethod(InvocableHandlerMethod).invokeForRequest(NativeWebRequest, ModelAndViewContainer, Object...) line: 131
//解析传入参数
ServletInvocableHandlerMethod(InvocableHandlerMethod).getMethodArgumentValues(NativeWebRequest, ModelAndViewContainer, Object...) line: 150
HandlerMethodArgumentResolverComposite.resolveArgument(MethodParameter, ModelAndViewContainer, NativeWebRequest, WebDataBinderFactory) line: 120
RequestParamMethodArgumentResolver(AbstractNamedValueMethodArgumentResolver).resolveArgument(MethodParameter, ModelAndViewContainer, NativeWebRequest, WebDataBinderFactory) line: 97
//调用处理方法，返回结果
ServletInvocableHandlerMethod(InvocableHandlerMethod).doInvoke(Object...) line: 207
//处理返回值
HandlerMethodReturnValueHandlerComposite.handleReturnValue(Object, MethodParameter, ModelAndViewContainer, NativeWebRequest) line: 78
RequestResponseBodyMethodProcessor.handleReturnValue(Object, MethodParameter, ModelAndViewContainer, NativeWebRequest) line: 175
//调用数据解析器
RequestResponseBodyMethodProcessor(AbstractMessageConverterMethodProcessor).writeWithMessageConverters(T, MethodParameter, ServletServerHttpRequest, ServletServerHttpResponse) line: 184
//调用fastjson序列化结果参数
FastJsonHttpMessageConverter.write(Object, Type, MediaType, HttpOutputMessage) line: 184
//视图解析
RequestMappingHandlerAdapter.getModelAndView(ModelAndViewContainer, ModelFactory, NativeWebRequest) line: 1000 - post请求
ApplicationFilterChain.internalDoFilter(ServletRequest, ServletResponse)
DispatcherServlet(HttpServlet).service(ServletRequest, ServletResponse)
DispatcherServlet(HttpServlet).service(HttpServletRequest, HttpServletResponse)
org.springframework.web.servlet.FrameworkServlet.doPost(HttpServletRequest, HttpServletResponse)
org.springframework.web.servlet.FrameworkServlet.doService(HttpServletRequest, HttpServletResponse)
org.springframework.web.servlet.DispatcherServlet.doService(HttpServletRequest, HttpServletResponse)
DispatcherServlet.doDispatch(HttpServletRequest, HttpServletResponse)
RequestMappingHandlerAdapter(AbstractHandlerMethodAdapter).handle(HttpServletRequest, HttpServletResponse, Object)
RequestMappingHandlerAdapter.handleInternal(HttpServletRequest, HttpServletResponse, HandlerMethod)
//调用处理器方法，执行请求，处理结果并且返回试图解析器
RequestMappingHandlerAdapter.invokeHandlerMethod(HttpServletRequest, HttpServletResponse, HandlerMethod)
//调用请求并且处理结果
ServletInvocableHandlerMethod.invokeAndHandle(ServletWebRequest, ModelAndViewContainer, Object...）
//1、调用请求
ServletInvocableHandlerMethod(InvocableHandlerMethod).invokeForRequest(NativeWebRequest, ModelAndViewContainer, Object...)
//1.1、解析传入参数
ServletInvocableHandlerMethod(InvocableHandlerMethod).getMethodArgumentValues(NativeWebRequest, ModelAndViewContainer, Object...)
//1.1.1
HandlerMethodArgumentResolverComposite.resolveArgument(MethodParameter, ModelAndViewContainer, NativeWebRequest, WebDataBinderFactory) line: 121
//1.1.2
RequestResponseBodyMethodProcessor.resolveArgument(MethodParameter, ModelAndViewContainer, NativeWebRequest, WebDataBinderFactory) line: 129
//1.2、执行方法，返回结果
ServletInvocableHandlerMethod(InvocableHandlerMethod).doInvoke(Object...)
//处理返回结果
HandlerMethodReturnValueHandlerComposite.handleReturnValue(Object, MethodParameter, ModelAndViewContainer, NativeWebRequest)
RequestResponseBodyMethodProcessor.handleReturnValue(Object, MethodParameter, ModelAndViewContainer, NativeWebRequest)
RequestResponseBodyMethodProcessor(AbstractMessageConverterMethodProcessor).writeWithMessageConverters(T, MethodParameter, ServletServerHttpRequest, ServletServerHttpResponse)
//调用实际序列化方法
FastJsonHttpMessageConverter.write(Object, Type, MediaType, HttpOutputMessage)
org.springframework.http.converter.AbstractHttpMessageConverter.write(T, MediaType, HttpOutputMessage)
com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter.writeInternal(Object, HttpOutputMessage)注意：作者使用springboot进行源码调试，因为版本问题有细微差别。
参考文章：https://www.cnblogs.com/canmeng-cn/p/9040395.html
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