1. Spring mvc 流程
其时序图：
整体流程图：
SpringMVC 工作流程描述：
- 用户向服务器发送请求，请求被Spring 前端控制Servelt
DispatcherServlet捕获； DispatcherServlet对请求URL进行解析，得到请求资源标识符（URI）。然后根据该URI，调用HandlerMapping获得该Handler配置的所有相关的对象（包括Handler对象以及Handler对象对应的拦截器），最后以HandlerExecutionChain对象的形式返回；DispatcherServlet根据获得的Handler，选择一个合适的HandlerAdapter。（附注：如果成功获得HandlerAdapter后，此时将开始执行拦截器的preHandler(…)方法）- 提取
Request中的模型数据，填充Handler入参，开始执行Handler（Controller)。 在填充Handler的入参过程中，根据你的配置，Spring将帮你做一些额外的工作：- HttpMessageConveter： 将请求消息（如Json、xml等数据）转换成一个对象，将对象转换为指定的响应信息
- 数据转换：对请求消息进行数据转换。如String转换成Integer、Double等
- 数据根式化：对请求消息进行数据格式化。 如将字符串转换成格式化数字或格式化日期等
- 数据验证： 验证数据的有效性（长度、格式等），验证结果存储到BindingResult或Error中
- Handler执行完成后，向
DispatcherServlet返回一个ModelAndView对象； - 根据返回的
ModelAndView，选择一个适合的ViewResolver（必须是已经注册到Spring容器中的ViewResolver)返回给DispatcherServlet； ViewResolver结合Model和View，来渲染视图- 将渲染结果返回给客户端。
2. HttpServlet & FrameworkServlet
下面我们先看看 DispatcherServlet 的两个父类： HttpServlet 和 FrameworkServlet 。
FrameworkServlet 重写了 HttpServlet 的 service 方法。 我们这里先来看看 FrameworkServlet#service 方法。
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 解析请求方式
HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
processRequest(request, response);
}
else {
super.service(request, response);
}
}
复制代码
这里我们需要关注两个点 ： processRequest(request, response); 和 super.service(request, response); 。下面我们一一来看
2.1 HttpServlet#service
我们知道 HttpServlet 类中分别提供了相应的服务方法( doGet、doPost 等)，如下图
同时， HttpServlet 会根据请求的不同形式引导到对应导函数中处理，如下 HttpServlet#service(HttpServletRequest, HttpServletResponse) ：
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String method = req.getMethod();
// 如果是 get 方法
if (method.equals(METHOD_GET)) {
// lastModified 缓存判断
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 {
// 如果设置了缓存时间，则判断在ifModifiedSince 之后的时间，是否被修改。
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);
}
}
}
// 分发不同的请求
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);
}
}
复制代码
而这几个函数最常用的就是 doGet() 和 doPost() 。这两个方法被 FrameworkServlet 重写了。我们来看看在 FrameworkServlet 中的实现。
@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);
}
...
复制代码
我们可以很清楚的看到，对于大部分的请求，还是依赖于 HttpServlet#service(HttpServletRequest, HttpServletResponse) 来进行一个请求的分发。对于我们常见的 doGet() 和 doPost() 方法都是直接调用 processRequest(request, response); ， 而 processRequest 方法 的具体实现在 FrameworkServlet#processRequest 中 。
2.2 FrameworkServlet#processRequest
因此。接下来我们就来看看 org.springframework.web.servlet.FrameworkServlet#processRequest :
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 记录当前时间，用于记录web请求的记录时间
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
// 1234 的目的是为了保证当前线程的 LocaleContext 和 RequestAttributes 在当前请求后还能恢复，所以提取保存
// 1. 提取当前线程的 LocaleContext 属性
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
// 2. 根据当前的request 创建对应的 LocaleContext ,并绑定到当前线程
LocaleContext localeContext = buildLocaleContext(request);
// 3. 提取当前线程的 RequestAttributes 属性
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
// 4. 根据当前的request 创建对应的 RequestAttributes ,并绑定到当前线程
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
initContextHolders(request, localeContext, requestAttributes);
try {
// todo 5. 委托给 doservice方法进行进一步处理
doService(request, response);
}
catch (ServletException | IOException ex) {
failureCause = ex;
throw ex;
}
catch (Throwable ex) {
failureCause = ex;
throw new NestedServletException("Request processing failed", ex);
}
finally {
// 6. 请求结束，恢复线程原状
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
logResult(request, response, failureCause, asyncManager);
// 发布请求结束的通知事件，无论成功与否
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
复制代码
由于逻辑都被封装到 doService(request, response); 中，所以这里还是比较简单。而doService又被 DispatcherServlet 实现了。因此我们这里来看看 DispatcherServlet#doService 。
- DispatcherServlet#doService
@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.
// 基本的东西保存到request作用域中 方便获取, 设置一些Spring 上下文
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());
// 闪存管理器，重定向携带数据
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 previousRequestPath = null;
if (this.parseRequestPath) {
previousRequestPath = (RequestPath) request.getAttribute(ServletRequestPathUtils.PATH_ATTRIBUTE);
ServletRequestPathUtils.parseAndCache(request);
}
try {
// todo 派发功能
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 (this.parseRequestPath) {
ServletRequestPathUtils.setParsedRequestPath(previousRequestPath, request);
}
}
}
复制代码
很显然，这 “爷仨” 一层一层传递，终于传递到了DispatcherServlet 手里，这里我们直接开始看 doDispatch(request, response); ，这里才是核心逻辑的所在。
3. DispatcherServlet#doDispatch
// SpringMVC处理请求的核心流程
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
// handler (目标方法)的执行链
HandlerExecutionChain mappedHandler = null;
// 文件上传标志
boolean multipartRequestParsed = false;
// 对异步请求的支持（Servlet3.0 以后才有的，Webflux）
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
// 1. 如果是 MultipartContent 类型的request 则转换request 为 MultipartHttpServletRequest 类型的request
// 检查 当前是否文件上传的请求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
// 2. 根据request 寻找对应的 handler
// todo 构造出了【目标方法+拦截器整个链路】 决定使用哪个Handler处理当前请求
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
// 3. 如果没有找到对应的handler，则通过 response 反馈错误信息
// 如果找不到处理，就报404错误
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
// 4. 根据当前的 handler 找到对应的HandlerAdapter
// todo 获取适配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
// 5. last-modified 的缓存处理
// 如果当前handler 支持 last-modified 头处理则进行缓存处理
String method = request.getMethod();
boolean isGet = HttpMethod.GET.matches(method);
// 如果是 get请求或者 head 请求则进入该分支
if (isGet || HttpMethod.HEAD.matches(method)) {
// todo 调用 HandlerAdapter#getLastModified 方法 来获取最后修改时间
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
// todo 判断到目前为止是否有过修改，没有则直接return。实现缓存的功能
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
// 6.1 执行 所有拦截器 的preHandle 方法，使用mappedHandler整个链
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
// todo 7. 真正执行目标方法，mappedHandler.getHandler() 并 返回视图
// 反射执行目标方法，确定参数值，处理返回值【封装成ModelAndView】
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// // 8. 视图名称转换应用于需要添加前缀的情况 默认的ViewName
applyDefaultViewName(processedRequest, mv);
// 6.2 执行 所有拦截器 的postHandle 方法，使用mappedHandler整个链
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
// 记录下来异常，在 9 中统一处理
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);
}
// todo 9. 处理最后的结果
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
// // 6.3 拦截器完成方法的调用 下面的即使执行完了，异常还是抛出去
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
// 6.3 拦截器完成方法的调用
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);
}
}
}
}
复制代码
DispatcherServlet#doDispatch 涉及的地方就比较多，下面我们一个一个看：
3.1 checkMultipart(request)
对于请求的处理，Spring首先考虑的是对 Multipart 的处理，如果是 MultipartContent 类型的request 则转换request 为 MultipartHttpServletRequest 类型的request。简单来说，就是判断是否是文件请求。
protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
// multipartResolver 文件上传解析器 isMultipart方法
if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
if (DispatcherType.REQUEST.equals(request.getDispatcherType())) {
logger.trace("Request already resolved to MultipartHttpServletRequest, e.g. by MultipartFilter");
}
}
else if (hasMultipartException(request)) {
logger.debug("Multipart resolution previously failed for current request - " +
"skipping re-resolution for undisturbed error rendering");
}
else {
try {
return this.multipartResolver.resolveMultipart(request);
}
catch (MultipartException ex) {
if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
logger.debug("Multipart resolution failed for error dispatch", ex);
// Keep processing error dispatch with regular request handle below
}
else {
throw ex;
}
}
}
}
// If not returned before: return original request.
return request;
}
复制代码
核心方法 this.multipartResolver.isMultipart(request) ，我们来看一 StandardServletMultipartResolver#isMultipart :
@Override
public boolean isMultipart(HttpServletRequest request) {
// 所有文件上传请求都会有这个
return StringUtils.startsWithIgnoreCase(request.getContentType(),
(this.strictServletCompliance ? MediaType.MULTIPART_FORM_DATA_VALUE : "multipart/"));
}
复制代码
3.2 getHandler(processedRequest);
这一步的目的是 根据request 信息遍历 HandlerMapping 找到对应的handler。 具体代码如下：
// DispatcherServlet#getHandler
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 这里的 this.handlerMappings 在没有手动调整的情况下是加载的默认配置文件中的数据
if (this.handlerMappings != null) {
// 遍历每一个 handleMapping，解析 request，直到碰到一个解析成功的，将解析后的 Handler拦截链路返回。
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
复制代码
关于 mapping.getHandler(request) 的处理。后面详细介绍。
3.3 noHandlerFound(processedRequest, response);
正常情况下，每一个请求都应该对应一个 Handler，因为每个请求都应该在后台有对应的处理逻辑。而逻辑的实现就是在Handler 中。正常情况下，如果没有URL匹配的Handler，我们可以通过设置默认的Handler 来解决这一问题，不过如果没有设置默认的Handler。则只能通过Response 向用户返回错误信息。
protected void noHandlerFound(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (pageNotFoundLogger.isWarnEnabled()) {
pageNotFoundLogger.warn("No mapping for " + request.getMethod() + " " + getRequestUri(request));
}
// 判断DispatcherServlet 属性设置，是否需要抛出异常
if (this.throwExceptionIfNoHandlerFound) {
throw new NoHandlerFoundException(request.getMethod(), getRequestUri(request),
new ServletServerHttpRequest(request).getHeaders());
}
else {
// 否则直接抛出错误 404
response.sendError(HttpServletResponse.SC_NOT_FOUND);
}
}
复制代码
3.4 getHandlerAdapter(mappedHandler.getHandler());
这一步的目的是根据 Handler 寻找对应的 HandlerAdapter 。这里使用了 适配器模式 ，遍历所有的 Adapter。根据 HandlerAdapter#supports 方法来判断是否支持当前Handler 的解析，如果支持，则返回。
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");
}
复制代码
我们这里返回的是RequestMappingHandlerAdapter，其判定条件如下：
@Override
public final boolean supports(Object handler) {
// supportsInternal((HandlerMethod) handler)) 返回 true
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
复制代码
3.5 Last-Modified 的缓存处理
在客户端第一次输入 URL 时，服务器端返回内容和200状态码，表示请求成功，同时会添加一个 “Last-Modified” 的响应头，表示此文件在服务器上最后的更新时间。
客户端第二次请求此URL时2，客户端会向服务器发送请求头 “If-Modified-Since”，询问服务器该时间之后当前请求是否有被修改过，如果服务端内容没有变化，则会自动返回 304 状态码（只要响应头，内容为空，这样就节省了带宽）。
Spring 实现 Last-Modified 机制，只需要实现 LastModified 接口就可以。如下：
@Component public class BeanNameSayController implements Controller, LastModified { private long lastModified;
@Override
public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
return new ModelAndView("/hello");
}
@Override
public long getLastModified(HttpServletRequest request) {
if (lastModified == 0L){
lastModified = System.currentTimeMillis();
}
return lastModified;
}
复制代码
}
后面具体分析。
3.6 拦截器的调用
我们添加的拦截器，会在下面这些地方被调用合适的方法。
3.6.1 mappedHandler.applyPreHandle(processedRequest, response)
逻辑很简单，遍历所有的拦截器，分别调用 preHandle 前置方法。
// org.springframework.web.servlet.HandlerExecutionChain#applyPreHandle
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
// 获取所有的拦截器
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
// 调用前置方法。如果有一个前置方法返回false，则直接调用完成方法
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
复制代码
3.6.2. mappedHandler.applyPostHandle(processedRequest, response, mv);
逻辑基本相同，没有什么区别，这里调用的是程序执行后的后置方法
// org.springframework.web.servlet.HandlerExecutionChain#applyPostHandle
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];
// 调用后置方法
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
复制代码
3.6.3 triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
调用拦截器结束方法(视图呈现之后)。
// org.springframework.web.servlet.DispatcherServlet#triggerAfterCompletion
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = this.interceptorIndex; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
try {
// 调用结束方法
interceptor.afterCompletion(request, response, this.handler, ex);
}
catch (Throwable ex2) {
logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
}
}
}
}
复制代码
3.7 ha.handle(processedRequest, response, mappedHandler.getHandler());
这里是真正调用 Handler 处理业务逻辑的地方。我们这里看的是 RequestMappingHandlerAdapter 。 ha.handle(processedRequest, response, mappedHandler.getHandler()); 方法会调用 RequestMappingHandlerAdapter#invokeHandlerMethod 方法。同时在这个方法里面，会通过反射的方式调用 HandlerMthoder 。并将返回结果封装成 ModelAndView 。
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
// 装饰器模式，把原生的request, response 封装到一个对象中 方便后续只用这一个参数就可以
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
// 数据绑定器
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
// 获取到模型工厂 Model(要交给页面的数据) View（我们要去的视图）
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
// 将 handlerMethod 转换成 ServletInvocableHandlerMethod
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
// 设置ServletInvocableHandlerMethod 的一些属性
// todo 参数解析器
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
// todo 返回值解析器
if (this.returnValueHandlers != null) {
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
// 模型和视图的容器，以后流程共享ModelAndView数据的临时存储器
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
// 异步请求
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);
}
// todo 开始执行目标方法，反射调用HandlerMethod
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
// todo 封装ModelAndView
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
复制代码
我们首先来看下 核心方法 invocableMethod.invokeAndHandle(webRequest, mavContainer); ：
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// todo 目标方法的反射执行
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 {
// todo 返回值的处理
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(formatErrorForReturnValue(returnValue), ex);
}
throw ex;
}
}
复制代码
3.7.1 请求参数解析器argumentResolvers
核心方法 invokeForRequest 中，
@Nullable
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// todo 获取方法的 请求参数
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
logger.trace("Arguments: " + Arrays.toString(args));
}
// 反射执行
return doInvoke(args);
}
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 拿到方法的所有参数
MethodParameter[] parameters = getMethodParameters();
if (ObjectUtils.isEmpty(parameters)) {
return EMPTY_ARGS;
}
// 准备args的数组，跟方法的参数长度一样，挨个确定每个参数都是什么值
Object[] args = new Object[parameters.length];
for (int i = 0; i < parameters.length; i++) {
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
// 先去已提供的参数里面查找
args[i] = findProvidedArgument(parameter, providedArgs);
if (args[i] != null) {
continue;
}
// todo 解析参数
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;
}
private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
// 先看缓存中有没有
HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
if (result == null) {
// 27个参数解析器 遍历执行
for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {
//
if (resolver.supportsParameter(parameter)) {
result = resolver;
// 支持这种参数的解析器也会被放到缓存中argumentResolverCache
this.argumentResolverCache.put(parameter, result);
break;
}
}
}
return result;
}
复制代码
一共有27种请求参数解析器，针对不同的参数进行使用不同的解析器。
执行目标方法就是通过反射执行的。
3.7.2 返回值参数解析器
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
复制代码
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
// todo 找到合适的返回值处理器
HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
if (handler == null) {
throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
}
// 处理返回值
handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
}
@Nullable
private HandlerMethodReturnValueHandler selectHandler(@Nullable Object value, MethodParameter returnType) {
boolean isAsyncValue = isAsyncReturnValue(value, returnType);
for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
if (isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler)) {
continue;
}
if (handler.supportsReturnType(returnType)) {
return handler;
}
}
return null;
}
复制代码
一共有15种返回值解析器。
有一个 RequestResponseBodyMethodProcessor ，只要你标注了@ResponseBody注解，使用这个处理器进行处理，将返回值数据直接返回。
3.7.3 封装ModelAndView
getModelAndView(mavContainer, modelFactory, webRequest);
@Nullable
private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
// modelFactory 准备模型数据，请求域数据共享，session里面的数据存储到请求域中
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) {
// todo 重定向数据的共享 RedictView ,先把数据转移到request,再把request转移到session中
RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
}
}
return mav;
}
复制代码
3.8 applyDefaultViewName(processedRequest, mv);
当 控制层的返回结果是 null 或者 void 时，则表明没有找到对应视图，Spring 会根据request 信息来进行解析，查找默认的视图。
private void applyDefaultViewName(HttpServletRequest request, @Nullable ModelAndView mv) throws Exception {
// 视图转换器应用于添加前后缀的情况
if (mv != null && !mv.hasView()) {
String defaultViewName = getDefaultViewName(request);
if (defaultViewName != null) {
mv.setViewName(defaultViewName);
}
}
}
复制代码
3.9 processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
这一步的作用是 集中处理请求异常并解析最终的ModelAndView，根据解析出来的视图跳转页面 。
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
@Nullable Exception exception) throws Exception {
boolean errorView = false;
// 判断上面的过程是否出现了异常。如果本次请求出现了异常，并不能因此终止程序。所以需要解析出来异常，返回对应的视图结果，告知用户出现了异常。
// 有异常的处理
if (exception != null) {
// 根据不同的异常类型解析返回不同的视图告知用户
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
// 定义无数种异常解析器就会得到不同的异常解析效果
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
// todo 处理异常的情况
// 如果所有异常都不能处理，这个异常就直接抛出去
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// 上面所有的异常解析器都没能处理这个异常，就不执行下面的逻辑了。。
// Did the handler return a view to render?
// 动态策略
// @ResponseBody（提前在解析返回值的时候，就已经把数据写出去了）
// 如果在Handler实例的处理过程中返回了 view，则需要做页面处理
if (mv != null && !mv.wasCleared()) {
// todo 渲染，来解析模型和视图
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) {
// Exception (if any) is already handled..
// 触发 拦截器完成事件
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
复制代码
3.9.1 render(mv, request, response);
在最后的处理中，一定会涉及页面的跳转问题。而在 render(mv, request, response); 完成了页面的跳转。
// org.springframework.web.servlet.DispatcherServlet#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();
// 如果viewname不为null，则需要通过viewName 解析出来对应的 View
if (viewName != null) {
// We need to resolve the view name.
// 解析视图名称
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 {
// 如果viewName 为null，则认为 ModelAndView 直接指定了View。不需要解析了。
// 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 {
// 设置视图状态。可能是 404， 500 等情况
if (mv.getStatus() != null) {
response.setStatus(mv.getStatus().value());
}
// 进行跳转逻辑
view.render(mv.getModelInternal(), request, response);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Error rendering view [" + view + "]", ex);
}
throw ex;
}
}
复制代码
resolveViewName(viewName, mv.getModelInternal(), locale, request); 是 通过视图解析器进行视图解析 。返回合适视图。具体实现如下。
// org.springframework.web.servlet.DispatcherServlet#resolveViewName
@Nullable
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，直到有解析器能解析出来视图
for (ViewResolver viewResolver : this.viewResolvers) {
View view = viewResolver.resolveViewName(viewName, locale);
if (view != null) {
return view;
}
}
}
return null;
}
复制代码
我们看一下 viewResolver.resolveViewName(viewName, locale) 方法。这里我们看 InternalResourceViewResolver#resolveViewName 方法，其方法是在父类 AbstractCachingViewResolver#resolveViewName 中实现，如下：
@Override
@Nullable
public View resolveViewName(String viewName, Locale locale) throws Exception {
// 如果没有缓存，则直接创建 View
if (!isCache()) {
return createView(viewName, locale);
}
else {
// 从缓存中获取视图
Object cacheKey = getCacheKey(viewName, locale);
View view = this.viewAccessCache.get(cacheKey);
if (view == null) {
synchronized (this.viewCreationCache) {
view = this.viewCreationCache.get(cacheKey);
if (view == null) {
// Ask the subclass to create the View object.
view = createView(viewName, locale);
if (view == null && this.cacheUnresolved) {
view = UNRESOLVED_VIEW;
}
if (view != null && this.cacheFilter.filter(view, viewName, locale)) {
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);
}
}
复制代码
createView 方法 被 UrlBasedViewResolver 重写了。 UrlBasedViewResolver#createView 具体如下：
@Override
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.
// 如果当前视图解析器无法解析该视图，则返回null
if (!canHandle(viewName, locale)) {
return null;
}
// Check for special "redirect:" prefix.
// 处理前缀为 "redirect:" (重定向)的情况
if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
RedirectView view = new RedirectView(redirectUrl,
isRedirectContextRelative(), isRedirectHttp10Compatible());
String[] hosts = getRedirectHosts();
if (hosts != null) {
view.setHosts(hosts);
}
return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
}
// Check for special "forward:" (请求转发)prefix.
// 处理前缀为 "forward:" 的情况
if (viewName.startsWith(FORWARD_URL_PREFIX)) {
String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
InternalResourceView view = new InternalResourceView(forwardUrl);
return applyLifecycleMethods(FORWARD_URL_PREFIX, view);
}
// Else fall back to superclass implementation: calling loadView.
// 调用父类的方法创建视图
return super.createView(viewName, locale);
}
复制代码
super.createView(viewName, locale); 调用 AbstractCachingViewResolver#createView 如下：
// org.springframework.web.servlet.view.AbstractCachingViewResolver#createView
protected View createView(String viewName, Locale locale) throws Exception {
return loadView(viewName, locale);
}
// org.springframework.web.servlet.view.UrlBasedViewResolver#loadView
@Override
protected View loadView(String viewName, Locale locale) throws Exception {
AbstractUrlBasedView view = buildView(viewName);
View result = applyLifecycleMethods(viewName, view);
return (view.checkResource(locale) ? result : null);
}
// org.springframework.web.servlet.view.UrlBasedViewResolver#buildView
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
Class<?> viewClass = getViewClass();
Assert.state(viewClass != null, "No view class");
AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
// 设置视图 url 添加前缀和后缀
view.setUrl(getPrefix() + viewName + getSuffix());
view.setAttributesMap(getAttributesMap());
String contentType = getContentType();
if (contentType != null) {
view.setContentType(contentType);
}
String requestContextAttribute = getRequestContextAttribute();
if (requestContextAttribute != null) {
view.setRequestContextAttribute(requestContextAttribute);
}
Boolean exposePathVariables = getExposePathVariables();
if (exposePathVariables != null) {
view.setExposePathVariables(exposePathVariables);
}
Boolean exposeContextBeansAsAttributes = getExposeContextBeansAsAttributes();
if (exposeContextBeansAsAttributes != null) {
view.setExposeContextBeansAsAttributes(exposeContextBeansAsAttributes);
}
String[] exposedContextBeanNames = getExposedContextBeanNames();
if (exposedContextBeanNames != null) {
view.setExposedContextBeanNames(exposedContextBeanNames);
}
return view;
}
复制代码
在 org.springframework.web.servlet.view.AbstractView#render 中完成了视图跳转。 对于 ModelView 的使用，我们可以将一些属性放入其中，然后在页面上通过 JSTL 语法或者 request 获取属性，这个功能的实现就是在这里完成的。实现原理很简单，就是将要用到的属性方法request中，以便在其他地方可以获取到。
@Override
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));
}
// 将要用到的属性放入到mergedModel 中
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
// 准备 Response
prepareResponse(request, response);
// 处理页面跳转。同时将 mergedModel 保存到request中
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}
复制代码
我们看一下 InternalResourceView#renderMergedOutputModel 方法：
@Override // 真真的渲染逻辑
protected void renderMergedOutputModel(
Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
// Expose the model object as request attributes.
// todo 暴露model的数据作为请求域 中的数据
exposeModelAsRequestAttributes(model, request);
// Expose helpers as request attributes, if any.
exposeHelpers(request);
// Determine the path for the request dispatcher.
String dispatcherPath = prepareForRendering(request, response);
// Obtain a RequestDispatcher for the target resource (typically a JSP).
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() + "]");
}
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() + "]");
}
// todo 转发
rd.forward(request, response);
}
}
复制代码
本文含有隐藏内容，请 开通VIP 后查看