SpringMVC请求流程处理源码剖析（我斑愿称你为最全）已完善最后总结
文章目录
- 前言
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- 前端控制器DispatcherServlet的继承结构分析及请求处理传递流程（一图胜万语）
- 1.根据请求url获取handler执行器链包含处理当前请求的处理器对象和处理器链 getHandler(processedRequest)方法；
- 2.根据handler链中的handler处理器获取对应的HandlerAdapter处理器适配器getHandlerAdapter(mappedHandler.getHandler());
- 3.依次执行handler链中拦截器数组中拦截器的preHandler方法，返回true继续执行，false直接return； mappedHandler.applyPreHandle(processedRequest, response)
- 4.使用刚刚获取的HandlerAdapter处理器适配器执行handler逻辑，返回ModelAndView对象。mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
- 5.结果视图对象处理（如果未指定view逻辑视图名则根据请求路径给一个默认的逻辑视图名称）applyDefaultViewName(processedRequest, mv);
- 6.依次执行handler链中拦截器数组中拦截器的postHandle方法mappedHandler.applyPostHandle(processedRequest, response, mv);
- 7.数据模型model封装到请求域中并请求转发到真正的视图进行视图渲染processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
- 8.依次执行handler链中拦截器数组中拦截器的afterCompletion方法⻚⾯已经跳转渲染完毕之后,响应到浏览器之前执⾏（用来捕获视图渲染时发生的异常)triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
- 总结SpringMVC处理请求的详细流程：
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前言
SpringMVC是一个应用于表现层的经典框架，其中M代表模型（数据模型[pojo/vo/po]+业务模型）主要作用是充当C——>V的数据传递介质，V代表view视图（jps、html）负责请求域中M的展示，C代表Controller控制器（Servlet）主要作用是接收请求调用业务层进行业务处理，并将处理结果转发到V或者直接响应给浏览器。
SpringMVC请求处理流程较为宏观的描述
- 请求到达DispatcherServlet（前端控制器）后，DispatcherServlet调用HandlerMapping（处理器映射器）查询对应handler（处理器）
- HandlerMapping根据请求的url获取对应的handler给到DispatcherServlet
- DispatcherServlet将获取到的handler给到HandlerAdapter（处理器适配器）执行处理器处理请求业务
- handler执行后返回ModelAndView给DispatcherServlet
- DispatcherServlet请求视图解析器去解析view根据逻辑视图名拼接前后缀获取真正视图
- DispatcherServlet将数据模型model封装到请求域中并请求转发到真正的视图进行视图渲染
- 将渲染完成的视图响应给浏览器
由上述流程可以看出DispatcherServlet是负责串联SpringMVC各大组件的核心类，同时也是第一个接触Request的类，我们的源码剖析之旅就从DispatcherServlet入手。
前端控制器DispatcherServlet的继承结构分析及请求处理传递流程（一图胜万语）
doDispatch源码：
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
// 声明handler执行器链包含handler和拦截器数组
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
//
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
// 声明ModelAndView
ModelAndView mv = null;
Exception dispatchException = null;
try {
// 检查是否文件上传请求如果是则返回MultipartHttpServletRequest不是则返回request原值
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
// 1.根据请求url获取handler执行器链包含处理当前请求的处理器对象和拦截器链
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
// 如果handler链为空，则返回404
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
// 2.根据handler链中的handler处理器获取对应的处理器适配器（由于handler的格式不固定有可能是实现Controller接口的类，
// 有可能是标记@RequestMapping的方法，所以不同的handler要对应不同适配器来执行handler业务逻辑）
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;
}
}
// 3.依次执行handler链中拦截器数组中拦截器的preHandler方法，返回true继续执行，false直接return
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
// 4.使用刚刚获取的HandlerAdapter处理器适配器执行handler逻辑，返回ModelAndView对象。
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// 5.结果视图对象处理（如果未指定view逻辑视图名则根据请求路径给一个默认的逻辑视图名称）
applyDefaultViewName(processedRequest, mv);
// 6.依次执行handler链中拦截器数组中拦截器的postHandle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);
}
// 7.数据模型model封装到请求域中并请求转发到真正的视图进行视图渲染
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
// 8.依次执行handler链中拦截器数组中拦截器的afterCompletion方法
//⻚⾯已经跳转渲染完毕之后,响应到浏览器之前执⾏（用来捕获视图渲染时发生的异常)
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
// 同8
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);
}
}
}
}
提示：下面将按照doDispatch中的请求处理流程的8个主要流程逐一分析
1.根据请求url获取handler执行器链包含处理当前请求的处理器对象和处理器链 getHandler(processedRequest)方法；
HandlerExecutionChain处理器链包括handler和拦截器数组，处理器链类结构：
public class HandlerExecutionChain {
private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
// 处理器对象
private final Object handler;
// 拦截器数组
@Nullable
private HandlerInterceptor[] interceptors;
@Nullable
private List<HandlerInterceptor> interceptorList;
private int interceptorIndex = -1;
//...省略若干方法
}
DIspatcherServlet的getHandler(processedRequest)方法
DIspatcherServlet.class
//处理器映射器集合
private List<HandlerMapping> handlerMappings;
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;
}
HandlerMapping为处理器映射器，用于缓存和获取url对应的处理器和拦截器。
private List handlerMappings; 为处理器映射器集合，目前有两种实现1.BeanNameURLHandlerMapping用于保存在标签里配置的url与Handler和Interceptor之间的映射关系，目前基本不用了；2.RequestMappingHandlerMapping用于保存通过@RequestMapping注解配置的url与Handler和Interceptor之间的映射关系，目前主流。
下面进入AbstractHandlerMapping#getHandler
AbstractHandlerMapping.java
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 匹配handler
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = obtainApplicationContext().getBean(handlerName);
}
// 匹配拦截器数组，将获取到的拦截器数组+handler封装到HandlerExecutionChain处理器链对象中
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (logger.isTraceEnabled()) {
logger.trace("Mapped to " + handler);
}
else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
logger.debug("Mapped to " + executionChain.getHandler());
}
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigurationSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
2.根据handler链中的handler处理器获取对应的HandlerAdapter处理器适配器getHandlerAdapter(mappedHandler.getHandler());
由于handler的格式不固定有可能是实现Controller接口的类，有可能是标记@RequestMapping的方法，所以不同的handler要对应不同适配器来执行handler业务逻辑，HandlerAdapter可以理解为利用反射机制执行handler逻辑的反射工具类。
DIspatcherServlet.class
// 处理器适配器集合
private List<HandlerAdapter> handlerAdapters;
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");
}
根据handler在private List handlerAdapters;处理器集合中选择合适的适配器
SpringMVC中自带了三个处理器适配器:
- HttpRequestHandlerAdapter，处理实现了HttpRequestHandler接口的handler
public boolean supports(Object handler) {
return (handler instanceof HttpRequestHandler);
}
- SimpleControllerHandlerAdapter，处理实现了Controller接口的handler
public boolean supports(Object handler) {
return (handler instanceof Controller);
}
- RequestMappingHandlerAdapter，处理被@RequestMapping注解标注的方法handler
public final boolean supports(Object handler) {
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
3.依次执行handler链中拦截器数组中拦截器的preHandler方法，返回true继续执行，false直接return； mappedHandler.applyPreHandle(processedRequest, response)
此处会遍历拦截器数组中全部连接器，并且一次执行其preHandler方法，由此可见拦截器的preHandler在handler逻辑之前执行，可在拦截器的preHandler方法中进行权限验证等操作。
HandlerExecutionChain.class
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];
// 调用拦截器的preHandler方法
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
4.使用刚刚获取的HandlerAdapter处理器适配器执行handler逻辑，返回ModelAndView对象。mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
a.进入ha.handle
AbstractHandlerMethodAdapter.java
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}
b.进入handleInternal
RequestMappingHandlerAdapter.java
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// Execute invokeHandlerMethod in synchronized block if required.
// 判断当前是否需要支持同一个session线性处理请求，保证session线程安全（可配置）
if (this.synchronizeOnSession) {
// 获取当前请求的session对象，如果尚未创建返回null。（如果getSession(true)是如尚未创建则会创建新session）
HttpSession session = request.getSession(false);
if (session != null) {
// 根据session获取唯一key进行加锁
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
// handler处理核心逻辑
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
// session=null时
// handler处理核心逻辑
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No synchronization on session demanded at all...
// session可以请求并行处理时
// handler处理核心逻辑
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
c.进入invokeHandlerMethod
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
if (this.returnValueHandlers != null) {
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
// 封装ModelAndView容器
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
LogFormatUtils.traceDebug(logger, traceOn -> {
String formatted = LogFormatUtils.formatValue(result, !traceOn);
return "Resume with async result [" + formatted + "]";
});
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
// handler核心处理逻辑
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
// 获取ModelAndView对象
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
d.进入invokeAndHandle
ServletInvocableHandlerMethod.class
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// handler执行核心逻辑
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
disableContentCachingIfNecessary(webRequest);
mavContainer.setRequestHandled(true);
return;
}
}
else if (StringUtils.hasText(getResponseStatusReason())) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
Assert.state(this.returnValueHandlers != null, "No return value handlers");
try {
// 获取结果处理器，处理handler返回值，保存到ModelAndView容器中。
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(formatErrorForReturnValue(returnValue), ex);
}
throw ex;
}
}
e.进入invokeForRequest
InvocableHandlerMethod.class
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 获取handler1执行所需参数
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
logger.trace("Arguments: " + Arrays.toString(args));
}
// 反射调用handler方法，执行handler中的逻辑
return doInvoke(args);
}
f.进入getMethodArgumentValues
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 获取当前handler方法的形参
MethodParameter[] parameters = getMethodParameters();
if (ObjectUtils.isEmpty(parameters)) {
return EMPTY_ARGS;
}
// 创建新数组，用于封装handler被调用时的实参（不同类型的形参获取方式不一样）
Object[] args = new Object[parameters.length];
// 遍历形参
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 {
// 根据形参获取实参
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;
}
g.进入resolveArgument
HandlerMethodArgumentResolverComposite.class
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
// 根据不同类型的参数获取不同的参数解析器。如：String的参数解析器AbstractNamedValueMethodArgumentResolver、Map的参数解析器MapMethodProcessor等
HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
if (resolver == null) {
throw new IllegalArgumentException("Unsupported parameter type [" +
parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
}
// 利用对应的参数解析器解析形参获取实参
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
此处以String的参数解析器AbstractNamedValueMethodArgumentResolver、Map的参数解析器MapMethodProcessor为例
h1.String的参数解析器AbstractNamedValueMethodArgumentResolver#resolveArgument里最终执行的是根据形参名称分别在请求头、请求Param中获取对应名称的参数
h2.Map的参数解析器MapMethodProcessor
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
// 直接返回ModelAndView容器中的Model作为实参，此处也可以解释：在方法中声明形参Map，Model，ModelMap 并向里面填充的内容都会被写到请求域中
return mavContainer.getModel();
}
i.拿到handler执行的实参后回到第e步的doInvoke(args)，反射调用handler方法
InvocableHandlerMethod.class
protected Object doInvoke(Object... args) throws Exception {
ReflectionUtils.makeAccessible(getBridgedMethod());
try {
// 反射调用执行handler方法
return getBridgedMethod().invoke(getBean(), args);
}
catch (IllegalArgumentException ex) {
assertTargetBean(getBridgedMethod(), getBean(), args);
String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
throw new IllegalStateException(formatInvokeError(text, args), ex);
}
catch (InvocationTargetException ex) {
// Unwrap for HandlerExceptionResolvers ...
Throwable targetException = ex.getTargetException();
if (targetException instanceof RuntimeException) {
throw (RuntimeException) targetException;
}
else if (targetException instanceof Error) {
throw (Error) targetException;
}
else if (targetException instanceof Exception) {
throw (Exception) targetException;
}
else {
throw new IllegalStateException(formatInvokeError("Invocation failure", args), targetException);
}
}
}
j.到此handler方法以执行完毕，下面应处理handler返回值，保存到ModelAndView容器中，回到步骤d的this.returnValueHandlers.handleReturnValue()方法
HandlerMethodReturnValueHandlerComposite.class
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
// 根据不同结果类型获取不同的结果处理器如：String类型的结果处理器ViewNameMethodReturnValueHandler、ModelAndView类型的结果处理器ModelAndViewMethodReturnValueHandler
HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
if (handler == null) {
throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
}
// 调用结果处理器完成handler返回值与ModelAndViewContainer的关系组装
handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
}
此处以String类型的结果处理器ViewNameMethodReturnValueHandler、ModelAndView类型的结果处理器ModelAndViewMethodReturnValueHandler为例子
k1.String类型的结果处理器ViewNameMethodReturnValueHandler#handleReturnValue
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
// 如果返回值是String时，将返回值作为逻辑视图保存到ModelAndViewContainer中的view里
if (returnValue instanceof CharSequence) {
String viewName = returnValue.toString();
mavContainer.setViewName(viewName);
// 返回值是否包含重定向关键字，如果包含设置RedirectModelScenario=true在视图渲染时会用到
if (isRedirectViewName(viewName)) {
mavContainer.setRedirectModelScenario(true);
}
}
else if (returnValue != null) {
// should not happen
throw new UnsupportedOperationException("Unexpected return type: " +
returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
}
}
k2.ModelAndView类型的结果处理器ModelAndViewMethodReturnValueHandler#handleReturnValue
当返回值是在handler中new ModelAndView时此处会与形参中的Map，Model等合并返回作为新的Model封装到容器中
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue == null) {
mavContainer.setRequestHandled(true);
return;
}
ModelAndView mav = (ModelAndView) returnValue;
if (mav.isReference()) {
String viewName = mav.getViewName();
mavContainer.setViewName(viewName);
if (viewName != null && isRedirectViewName(viewName)) {
mavContainer.setRedirectModelScenario(true);
}
}
else {
View view = mav.getView();
mavContainer.setView(view);
if (view instanceof SmartView && ((SmartView) view).isRedirectView()) {
mavContainer.setRedirectModelScenario(true);
}
}
mavContainer.setStatus(mav.getStatus());
// 当返回值是在handler中new ModelAndView时此处会与形参中的Map，Model等合并返回作为新的Model封装到容器中
mavContainer.addAllAttributes(mav.getModel());
}
l.到此handler的结果值以封装到ModelAndView容器ModelAndViewContainer中回到步骤c的 getModelAndView(mavContainer, modelFactory, webRequest);方法中，获取ModeAndView对象并返回
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
modelFactory.updateModel(webRequest, mavContainer);
if (mavContainer.isRequestHandled()) {
return null;
}
ModelMap model = mavContainer.getModel();
ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
if (!mavContainer.isViewReference()) {
mav.setView((View) mavContainer.getView());
}
if (model instanceof RedirectAttributes) {
Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
if (request != null) {
RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
}
}
return mav;
}
5.结果视图对象处理（如果未指定view逻辑视图名则根据请求路径给一个默认的逻辑视图名称）applyDefaultViewName(processedRequest, mv);
进入applyDefaultViewName
DIspatcherServlet.class
private void applyDefaultViewName(HttpServletRequest request, @Nullable ModelAndView mv) throws Exception {
if (mv != null && !mv.hasView()) {
// 在请求中根据url获取默认视图名称
String defaultViewName = getDefaultViewName(request);
if (defaultViewName != null) {
mv.setViewName(defaultViewName);
}
}
}
进入getDefaultViewName
//默认视图名转换器组件 DefaultRequestToViewNameTranslator (SpringMVC9大组件之一)
DIspatcherServlet.class
private RequestToViewNameTranslator viewNameTranslator;
protected String getDefaultViewName(HttpServletRequest request) throws Exception {
// 如果初始化了默认视图名转换器组件则
return (this.viewNameTranslator != null ? this.viewNameTranslator.getViewName(request) : null);
}
进入getViewName
6.依次执行handler链中拦截器数组中拦截器的postHandle方法mappedHandler.applyPostHandle(processedRequest, response, mv);
此处会遍历拦截器数组中全部连接器，并且一次执行其postHandle方法，由此可见拦截器的postHandle在handler逻辑之后，视图渲染之前执行，可在拦截器的postHandle方法中对ModelAndView值进行修改。
进入applyPostHandle方法
HandlerExecutionChain.class
public void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
// 循环调用拦截器的postHandler方法
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
7.数据模型model封装到请求域中并请求转发到真正的视图进行视图渲染processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
进入a.processDispatchResult
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
@Nullable Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
// 视图渲染核心方法
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("No view rendering, null ModelAndView returned.");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
//8.当页面渲染请求转发后无异常时也会依次执行handler链中拦截器数组中拦截器的afterCompletion方法
//afterCompletion方法在⻚⾯已经跳转渲染完毕之后,响应到浏览器之前执⾏（用来捕获视图渲染时发生的异常)
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
b.进入render
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
// Determine locale for request and apply it to the response.
Locale locale =
(this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
response.setLocale(locale);
View view;
String viewName = mv.getViewName();
if (viewName != null) {
// We need to resolve the view name.
// 根据逻辑视图名解析封装实际视图
view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
if (view == null) {
throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
"' in servlet with name '" + getServletName() + "'");
}
}
else {
// No need to lookup: the ModelAndView object contains the actual View object.
view = mv.getView();
if (view == null) {
throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
"View object in servlet with name '" + getServletName() + "'");
}
}
// Delegate to the View object for rendering.
if (logger.isTraceEnabled()) {
logger.trace("Rendering view [" + view + "] ");
}
try {
if (mv.getStatus() != null) {
response.setStatus(mv.getStatus().value());
}
// 请求域数据封装，视图跳转（RedirectView重定向，AbstractUrlBasedView请求转发）
view.render(mv.getModelInternal(), request, response);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Error rendering view [" + view + "]", ex);
}
throw ex;
}
}
c.进入resolveViewName，View是个接口，根据不同的逻辑视图名称，会创建出不同的View实现
DIspatcherServlet.class
// 视图解析器SpringMVC的九大组件之一需在xml中配置InternalResourceViewResolver（extends UrlBasedViewResolver），主要作用设置视图前缀后缀
private List<ViewResolver> viewResolvers;
protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
Locale locale, HttpServletRequest request) throws Exception {
if (this.viewResolvers != null) {
// 遍历视图解析器，找到合适的视图解析器解析视图
for (ViewResolver viewResolver : this.viewResolvers) {
View view = viewResolver.resolveViewName(viewName, locale);
if (view != null) {
return view;
}
}
}
return null;
}
d.进入resolveViewName
AbstractCachingViewResolver.class
public View resolveViewName(String viewName, Locale locale) throws Exception {
if (!isCache()) {
return createView(viewName, locale);
}
else {
// 默认开启视图缓存机制，视图渲染跳转过一次后会进行缓存
Object cacheKey = getCacheKey(viewName, locale);
View view = this.viewAccessCache.get(cacheKey);
if (view == null) {
// 如果缓存中不存在该视图
synchronized (this.viewCreationCache) {
// 防止并发不安全锁内再判断一边
view = this.viewCreationCache.get(cacheKey);
if (view == null) {
// Ask the subclass to create the View object.
// 创建视图核心逻辑
view = createView(viewName, locale);
if (view == null && this.cacheUnresolved) {
view = UNRESOLVED_VIEW;
}
if (view != null) {
this.viewAccessCache.put(cacheKey, view);
this.viewCreationCache.put(cacheKey, view);
}
}
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace(formatKey(cacheKey) + "served from cache");
}
}
return (view != UNRESOLVED_VIEW ? view : null);
}
}
e.进入createView，根据逻辑视图名中不同的关键字获取不同类型的View实现如包含关键字"redirect:"创建RedirectView，包含关键字"forward"创建关键字InternalResourceView
protected View createView(String viewName, Locale locale) throws Exception {
// If this resolver is not supposed to handle the given view,
// return null to pass on to the next resolver in the chain.
if (!canHandle(viewName, locale)) {
return null;
}
// Check for special "redirect:" prefix.
// 判断是否包含重定向关键字
if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
// 封装重定向视图
RedirectView view = new RedirectView(redirectUrl,
isRedirectContextRelative(), isRedirectHttp10Compatible());
String[] hosts = getRedirectHosts();
if (hosts != null) {
view.setHosts(hosts);
}
// 将视图加载到Spring容器
return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
}
// Check for special "forward:" prefix.
// 判断是否包含请求转发关键字
if (viewName.startsWith(FORWARD_URL_PREFIX)) {
String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
// 封装请求转发资源视图InternalResourceView extends AbstractUrlBasedView
InternalResourceView view = new InternalResourceView(forwardUrl);
// 将视图加载到Spring容器
return applyLifecycleMethods(FORWARD_URL_PREFIX, view);
}
// Else fall back to superclass implementation: calling loadView.
// 创建正常视图AbstractUrlBasedView（正常视图后面渲染流转也是走forward请求转发）
return super.createView(viewName, locale);
}
f.至此真正视图对象以获取，下面我们回到b步骤的view.render(mv.getModelInternal(), request, response);
请求域数据封装，视图跳转（RedirectView重定向，InternalResourceView请求转发）
AbstractView.class
public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
logger.debug("View " + formatViewName() +
", model " + (model != null ? model : Collections.emptyMap()) +
(this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
}
// 合并model
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
// 准备响应设置参数
prepareResponse(request, response);
// 请求域数据封装+请求转发
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}
g1.进入RedirectView实现核心步骤RedirectView#renderMergedOutputModel
此处也解释了SpringMVC重定向请求数据传递的原理
RedirectView.class
protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request,
HttpServletResponse response) throws IOException {
String targetUrl = createTargetUrl(model, request);
targetUrl = updateTargetUrl(targetUrl, model, request, response);
// Save flash attributes
//向session中添加Flash属性用于重定向传递参数
RequestContextUtils.saveOutputFlashMap(targetUrl, request, response);
// Redirect
// 完成重定向response.sendRedirect(encodedURL);
sendRedirect(request, response, targetUrl, this.http10Compatible);
}
g2.进入InternalResourceView实现核心步骤InternalResourceView#renderMergedOutputModel
protected void renderMergedOutputModel(
Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
// Expose the model object as request attributes.
// 将model中的数据封装到请求域里request.setAttribute(name, value);
exposeModelAsRequestAttributes(model, request);
// Expose helpers as request attributes, if any.
exposeHelpers(request);
// Determine the path for the request dispatcher.
// 获取真实视图地址
String dispatcherPath = prepareForRendering(request, response);
// Obtain a RequestDispatcher for the target resource (typically a JSP).
// 封装请求转发器javax.servlet.RequestDispatcher
RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
if (rd == null) {
throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +
"]: Check that the corresponding file exists within your web application archive!");
}
// If already included or response already committed, perform include, else forward.
if (useInclude(request, response)) {
response.setContentType(getContentType());
if (logger.isDebugEnabled()) {
logger.debug("Including [" + getUrl() + "]");
}
// 注： 当前response是否已经设置了响应值，列入在某个拦截器或者Servlet中进行了处理，则会抛出异常，阻止当前跳转，响应之前设置的内容
rd.include(request, response);
}
else {
// Note: The forwarded resource is supposed to determine the content type itself.
if (logger.isDebugEnabled()) {
logger.debug("Forwarding to [" + getUrl() + "]");
}
// 请求转发
rd.forward(request, response);
}
}
注：至此视图的渲染和跳转已完成，等待当前请求的全部方法栈执行完毕后，浏览器即可看到调转效果，这里特别提一下回到a的mappedHandler.triggerAfterCompletion(request, response, null);当视图渲染跳转过程中无异常时，最后也会执行一遍流程8，也就是遍历调用拦截器的afterCompletion方法，此时异常为null
8.依次执行handler链中拦截器数组中拦截器的afterCompletion方法⻚⾯已经跳转渲染完毕之后,响应到浏览器之前执⾏（用来捕获视图渲染时发生的异常)triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
此处会遍历拦截器数组中全部连接器，并且一次执行其triggerAfterCompletion方法，由此可见拦截器的triggerAfterCompletion在视图渲染之后并且出现渲染异常时调用，可以在拦截器的triggerAfterCompletion方法中进行异常捕获。
总结SpringMVC处理请求的详细流程：
1.请求到达DispatcherServlet前端控制器，DispatcherServlet遍历处理器映射器HandlerMapping集合,根据请求的url匹配对应的处理器链HandlerExecutionChain包含一个Handler处理器和一个拦截器HandlerInterceptor[]数组。
2.DispatcherServlet遍历处理器适配器HandlerAdapter集合，根据处理器链中的Handler匹配对应的处理器适配器。
3.DispatcherServlet遍历处理器链中的拦截器数组，执行每个拦截器的preHandle方法（可在拦截器此方法中进行权限验证）
4.DispatcherServlet委派HandlerAdapter执行Handler业务方法，遍历handler的形参，根据不同的形参类型获取不同的HandlerMethodArgumentResolver参数解析器，调用参数解析器获取实参，获取实参后反射调用handler方法并保存方法returnValue返回值，根据返回值的类型获取对应的结果处理器，调用结果处理器将returnValue封装为ModelAndView返回DispatcherServlet.
5.检测ModelAndView中是否包含逻辑视图名称，如果逻辑视图名称为空则调用DefaultRequestToViewNameTranslator默认视图名称转换器 获取默认逻辑视图名称。
6.DispatcherServlet遍历处理器链中的拦截器数组，执行每个拦截器的postHandle方法
7.DIspatcherServlet遍历ViewResolver视图解析器数组获取对应的视图解析器，根据逻辑视图名称获取不同类型的View视图实现如（重定向视图RedirectView、请求转发资源视图InternalResourceView），获取到视图后将model数据写入请求域，然后进行请求转发或者重定向处理跳转到视图进行渲染。
8.当视图渲染完成或者渲染中出错时DispatcherServlet遍历处理器链中的拦截器数组，执行每个拦截器的afterCompletion方法
9.当前请求的全部方法栈执行完毕后Tomcat将渲染好的视图响应给浏览器。