首先看下doDispatch()方法如何找到适合的适配器来执行方法的：
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
Iterator i$ = this.handlerAdapters.iterator();
HandlerAdapter ha;
do {
if (!i$.hasNext()) {
throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
ha = (HandlerAdapter)i$.next();
if (this.logger.isTraceEnabled()) {
this.logger.trace("Testing handler adapter [" + ha + "]");
}
} while(!ha.supports(handler)); //遍历初始化时候保存好的适配器，通过执行每个适配器的supports方法，如果支持就是他了。
return ha;
}
注： 这块也有点责任链模式的意思...
下面看下RequestMappingHandlerAdapter是怎么实现support方法的，看之前先上类图。
实际上support方法是在AbstractHandlerMethodAdapter这个父类实现的，然后给自己留个钩子方法，让子类实现
public final boolean supports(Object handler) {
return handler instanceof HandlerMethod && this.supportsInternal((HandlerMethod)handler);
}
protected abstract boolean supportsInternal(HandlerMethod var1); //钩子方法
这里RequestMappingHandlerAdapter的supportInternal直接是返回的true，估计后续扩展其他子类可能会复杂些，这就是设计模式的好处。
这样就找到了合适的适配器，下面来看执行：
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
mappedHandler = this.getHandler(processedRequest, false); //获取处理器
if (mappedHandler == null || mappedHandler.getHandler() == null) {
this.noHandlerFound(processedRequest, response);
return;
}
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler()); //获取适配器
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (this.logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
this.logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
}
if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
return;
}
} //这一块是处理重复请求？？？ 有大神知道请留言....
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
} //执行拦截器的preHandle方法
try {
mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //执行真正的Controller方法，就是我们的方法
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
this.applyDefaultViewName(request, mv); //设置视图名称
mappedHandler.applyPostHandle(processedRequest, response, mv); //执行拦截器的postHandle方法
} catch (Exception var28) {
dispatchException = var28;
}
this.processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);//渲染视图
} catch (Exception var29) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var29);
} catch (Error var30) {
this.triggerAfterCompletionWithError(processedRequest, response, mappedHandler, var30);
}
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); //执行拦截器的afterConcurrentHandlingStarted
return;
} else {
if (multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}
}
}
}
拦截器这里就不在多说，这块就是返回false就不在往下执行。下面我们重点满ha.handle()方法，是如果映射参数，找到我们的方法，封装结果的。
类图前面已经展示了，实际上handle是在父类AbstractHandlerMethodAdapter实现的
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
return this.handleInternal(request, response, (HandlerMethod)handler); //子类实现这个方法
}
protected abstract ModelAndView handleInternal(HttpServletRequest var1, HttpServletResponse var2, HandlerMethod var3) throws Exception;
protected final ModelAndView handleInternal(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
if (this.getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
this.checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true);
} else {
this.checkAndPrepare(request, response, true);
} //看代码应该是从session中获取一些信息，然后初始化header等信息，不知道准确不？请大家指正！
//这块就是根据需要是否进行同步操作
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized(mutex) {
return this.invokeHandleMethod(request, response, handlerMethod);
}
}
}
//正式进入执行环节
return this.invokeHandleMethod(request, response, handlerMethod);
}
下面这个方法非常重要，将重点讲解：
private ModelAndView invokeHandleMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
WebDataBinderFactory binderFactory = this.getDataBinderFactory(handlerMethod); //创建@InitBinder注解的方法的工厂类，进行缓存
ModelFactory modelFactory = this.getModelFactory(handlerMethod, binderFactory);//创建@ModelAttribute@ControllerAdvice注解方法工厂并缓存
ServletInvocableHandlerMethod requestMappingMethod = this.createRequestMappingMethod(handlerMethod, binderFactory);
ModelAndViewContainer mavContainer = new ModelAndViewContainer(); //创建结果容器并初始化一些参数，
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);//执行@ModelAttribute注解的方法，将结果放到结果容器中
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response); //下面异步这一块不太明白，等后续在慢慢分析
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()[];
asyncManager.clearConcurrentResult();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Found concurrent result value [" + result + "]");
}
requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);
}
requestMappingMethod.invokeAndHandle(webRequest, mavContainer, new Object[]); //继续执行方法
return asyncManager.isConcurrentHandlingStarted() ? null : this.getModelAndView(mavContainer, modelFactory, webRequest); //返回值了，两种情况
}
public final void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
Object returnValue = this.invokeForRequest(webRequest, mavContainer, providedArgs); //执行方法，获取返回值
this.setResponseStatus(webRequest);
if (returnValue == null) {
if (this.isRequestNotModified(webRequest) || this.hasResponseStatus() || mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
} else if (StringUtils.hasText(this.responseReason)) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
try { //处理返回值 ，封装结果集
this.returnValueHandlers.handleReturnValue(returnValue, this.getReturnValueType(returnValue), mavContainer, webRequest);
} catch (Exception var6) {
if (this.logger.isTraceEnabled()) {
this.logger.trace(this.getReturnValueHandlingErrorMessage("Error handling return value", returnValue), var6);
}
throw var6;
}
}
public final Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
Object[] args = this.getMethodArgumentValues(request, mavContainer, providedArgs); //处理 参数
if (this.logger.isTraceEnabled()) {
StringBuilder builder = new StringBuilder("Invoking [");
builder.append(this.getMethod().getName()).append("] method with arguments ");
builder.append(Arrays.asList(args));
this.logger.trace(builder.toString());
}
Object returnValue = this.invoke(args); //反射执行方法
if (this.logger.isTraceEnabled()) {
this.logger.trace("Method [" + this.getMethod().getName() + "] returned [" + returnValue + "]");
}
return returnValue;
}
private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
MethodParameter[] parameters = this.getMethodParameters();
Object[] args = new Object[parameters.length];
for(int i = ; i < parameters.length; ++i) { //遍历方法的所有参数
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
GenericTypeResolver.resolveParameterType(parameter, this.getBean().getClass()); //获取设置参数类型
args[i] = this.resolveProvidedArgument(parameter, providedArgs);
if (args[i] == null) {
if (this.argumentResolvers.supportsParameter(parameter)) { //这块是遍历预置的参数解析器，就是前面说的责任链模式，**composite负责查找和执行
try { //由找到的参数解析器，来解析参数
args[i] = this.argumentResolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
} catch (Exception var9) {
if (this.logger.isTraceEnabled()) {
this.logger.trace(this.getArgumentResolutionErrorMessage("Error resolving argument", i), var9);
}
throw var9;
}
} else if (args[i] == null) {
String msg = this.getArgumentResolutionErrorMessage("No suitable resolver for argument", i);
throw new IllegalStateException(msg);
}
}
}
return args;
}
这块以，没有任何注解，参数为javaBean的解析器为例：ModelAttributeMethodProcessor
public boolean supportsParameter(MethodParameter parameter) {
if (parameter.hasParameterAnnotation(ModelAttribute.class)) {
return true;
} else if (this.annotationNotRequired) {
return !BeanUtils.isSimpleProperty(parameter.getParameterType());
} else {
return false;
}
}
public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest request, WebDataBinderFactory binderFactory) throws Exception {
String name = ModelFactory.getNameForParameter(parameter); //如果当前参数用@ModelAttribute修饰了，返回value值或者参数类型第一个字母小写
// 获取需要绑定的表单对象，看参数容器包含name为key的对象不，有的话就用它，没有创建个新的。
Object attribute = mavContainer.containsAttribute(name) ? mavContainer.getModel().get(name) : this.createAttribute(name, parameter, binderFactory, request);
WebDataBinder binder = binderFactory.createBinder(request, attribute, name);
if (binder.getTarget() != null) {
this.bindRequestParameters(binder, request);
this.validateIfApplicable(binder, parameter);
if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {
throw new BindException(binder.getBindingResult());
}
}
//以上就是参数绑定， 这块领开一篇文章详细说
Map<String, Object> bindingResultModel = binder.getBindingResult().getModel();
mavContainer.removeAttributes(bindingResultModel);
mavContainer.addAllAttributes(bindingResultModel);
return binder.getTarget();
}
参数就这样遍历处理，然后就开始通过反射 invoke执行了。接下来我们看是怎么封装换回结果的
try {
this.returnValueHandlers.handleReturnValue(returnValue, this.getReturnValueType(returnValue), mavContainer, webRequest);
} catch (Exception var6) {
if (this.logger.isTraceEnabled()) {
this.logger.trace(this.getReturnValueHandlingErrorMessage("Error handling return value", returnValue), var6);
}
throw var6;
}
this.returnValuehandlers. 就是那个返回结果的包装类，初始化的结果解析器就保存这里，处理思路和参数解析器一样的，
public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
HandlerMethodReturnValueHandler handler = this.getReturnValueHandler(returnType);
Assert.notNull(handler, "Unknown return value type [" + returnType.getParameterType().getName() + "]");
handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
}
private HandlerMethodReturnValueHandler getReturnValueHandler(MethodParameter returnType) {
Iterator i$ = this.returnValueHandlers.iterator();
HandlerMethodReturnValueHandler returnValueHandler;
do {
if (!i$.hasNext()) {
return null;
}
returnValueHandler = (HandlerMethodReturnValueHandler)i$.next();
if (this.logger.isTraceEnabled()) {
this.logger.trace("Testing if return value handler [" + returnValueHandler + "] supports [" + returnType.getGenericParameterType() + "]");
}
} while(!returnValueHandler.supportsReturnType(returnType));
return returnValueHandler;
}
遍历预置的所有结果解析器，结果解析器统一实现HandlerMethodReturnValueHandler 接口，实现supportReturnType方法：
这里我们距离用@ResponseBody注解的结果解析器RequestResponseBodyMethodProcessor 前面说了，参数和结果集他都实现了
public boolean supportsReturnType(MethodParameter returnType) {
return returnType.getMethodAnnotation(ResponseBody.class) != null; //判断是否有@ResponseBody注解
}
public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException {
mavContainer.setRequestHandled(true);
if (returnValue != null) {
this.writeWithMessageConverters(returnValue, returnType, webRequest); //用内置的消息转换器来转换结果集
}
}
这里可能有人会问，消息转换器什么时候加载的？是在RequestMappingHandlerAdapter这个bean实例化的时候加载的，同时加载参数和结果解析器时候注入到解析器当中的
public RequestMappingHandlerAdapter() { //无参构造函数中初始化
StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
stringHttpMessageConverter.setWriteAcceptCharset(false);
this.messageConverters = new ArrayList();
this.messageConverters.add(new ByteArrayHttpMessageConverter());
this.messageConverters.add(stringHttpMessageConverter);
this.messageConverters.add(new SourceHttpMessageConverter());
this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
}
private List<HandlerMethodReturnValueHandler> getDefaultReturnValueHandlers() { //构造参数解析器时候，注入进去
List<HandlerMethodReturnValueHandler> handlers = new ArrayList();
handlers.add(new ModelAndViewMethodReturnValueHandler());
handlers.add(new ModelMethodProcessor());
handlers.add(new ViewMethodReturnValueHandler());
handlers.add(new HttpEntityMethodProcessor(this.getMessageConverters(), this.contentNegotiationManager));
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));
handlers.add(new ModelAttributeMethodProcessor(false));
handlers.add(new RequestResponseBodyMethodProcessor(this.getMessageConverters(), this.contentNegotiationManager));
handlers.add(new ViewNameMethodReturnValueHandler());
handlers.add(new MapMethodProcessor());
if (this.getCustomReturnValueHandlers() != null) {
handlers.addAll(this.getCustomReturnValueHandlers());
}
if (!CollectionUtils.isEmpty(this.getModelAndViewResolvers())) {
handlers.add(new ModelAndViewResolverMethodReturnValueHandler(this.getModelAndViewResolvers()));
} else {
handlers.add(new ModelAttributeMethodProcessor(true));
}
return handlers;
}
下面来看是怎么寻找可以合适的消息转换器的
protected <T> void writeWithMessageConverters(T returnValue, MethodParameter returnType, NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException {
ServletServerHttpRequest inputMessage = this.createInputMessage(webRequest);
ServletServerHttpResponse outputMessage = this.createOutputMessage(webRequest);
this.writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
}
protected <T> void writeWithMessageConverters(T returnValue, MethodParameter returnType, ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage) throws IOException, HttpMediaTypeNotAcceptableException {
Class<?> returnValueClass = returnValue.getClass();
HttpServletRequest servletRequest = inputMessage.getServletRequest();
List<MediaType> requestedMediaTypes = this.getAcceptableMediaTypes(servletRequest); //获取请求的MediaType,eg："application/json"
List<MediaType> producibleMediaTypes = this.getProducibleMediaTypes(servletRequest, returnValueClass); //寻找支持这个返回类型的转换器支持的MediaTyoe
Set<MediaType> compatibleMediaTypes = new LinkedHashSet();
Iterator i$ = requestedMediaTypes.iterator();
//双循环两个list，进行匹配，把复核条件的MediaType放到compatibleMediaTypes中 //TODO有些不懂得是为啥这块要过滤一遍， 后面实现了 父类也做了判断每个字类是否支持MediaType了？？
MediaType selectedMediaType;
Iterator i$;
MediaType mediaType;
while(i$.hasNext()) {
selectedMediaType = (MediaType)i$.next();
i$ = producibleMediaTypes.iterator();
while(i$.hasNext()) {
mediaType = (MediaType)i$.next();
if (selectedMediaType.isCompatibleWith(mediaType)) {
compatibleMediaTypes.add(this.getMostSpecificMediaType(selectedMediaType, mediaType));
}
}
}
if (compatibleMediaTypes.isEmpty()) {
throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes);
} else {
List<MediaType> mediaTypes = new ArrayList(compatibleMediaTypes);
MediaType.sortBySpecificityAndQuality(mediaTypes);
selectedMediaType = null;
i$ = mediaTypes.iterator();
//排序之后，选择适合的MediaType
while(i$.hasNext()) {
mediaType = (MediaType)i$.next();
if (mediaType.isConcrete()) {
selectedMediaType = mediaType;
break;
}
if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION)) {
selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
break;
}
}
if (selectedMediaType != null) {
selectedMediaType = selectedMediaType.removeQualityValue();
i$ = this.messageConverters.iterator();
//遍历所有消息转换器，canWrite是接口方法，相当于前面的support等，模式都是一个。然后满足的进行write。输出结果。
while(i$.hasNext()) {
HttpMessageConverter<?> messageConverter = (HttpMessageConverter)i$.next();
if (messageConverter.canWrite(returnValueClass, selectedMediaType)) {
messageConverter.write(returnValue, selectedMediaType, outputMessage);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Written [" + returnValue + "] as \"" + selectedMediaType + "\" using [" + messageConverter + "]");
}
return;
}
}
}
throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes);
}
}
下面介绍下，@ResponseBode标签用的消息转换器是MappingJacksonHttpMessageConverter；先看下类图吧
MappingJacksonHttpMessageConverter重写了父类的write方法：
public boolean canWrite(Class<?> clazz, MediaType mediaType) {
return this.objectMapper.canSerialize(clazz) && this.canWrite(mediaType); //canWrite(mediaType)是父类实现的
}
protected boolean canWrite(MediaType mediaType) {
if (mediaType != null && !MediaType.ALL.equals(mediaType)) {
Iterator i$ = this.getSupportedMediaTypes().iterator(); //获取子类解析器支持的MediaType，看下是否支持
MediaType supportedMediaType;
do {
if (!i$.hasNext()) {
return false;
}
supportedMediaType = (MediaType)i$.next();
} while(!supportedMediaType.isCompatibleWith(mediaType));
return true;
} else {
return true;
}
}
write方法 父类也帮着实现了，父类具体做了如输出，拼凑输出流头等信息
public final void write(T t, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
HttpHeaders headers = outputMessage.getHeaders();
if (headers.getContentType() == null) {
if (contentType == null || contentType.isWildcardType() || contentType.isWildcardSubtype()) {
contentType = this.getDefaultContentType(t);
}
if (contentType != null) {
headers.setContentType(contentType);
}
}
if (headers.getContentLength() == -1L) {
Long contentLength = this.getContentLength(t, headers.getContentType());
if (contentLength != null) {
headers.setContentLength(contentLength);
}
}
this.writeInternal(t, outputMessage); //钩子方法，让子类去实现
outputMessage.getBody().flush();
}
protected void writeInternal(Object object, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
JsonEncoding encoding = this.getJsonEncoding(outputMessage.getHeaders().getContentType());
JsonGenerator jsonGenerator = this.objectMapper.getJsonFactory().createJsonGenerator(outputMessage.getBody(), encoding);
if (this.objectMapper.getSerializationConfig().isEnabled(Feature.INDENT_OUTPUT)) {
jsonGenerator.useDefaultPrettyPrinter();
}
//这块就是默认用Jackson进行翻译结果集了
try {
if (this.prefixJson) {
jsonGenerator.writeRaw("{} && ");
}
this.objectMapper.writeValue(jsonGenerator, object);
} catch (JsonProcessingException var6) {
throw new HttpMessageNotWritableException("Could not write JSON: " + var6.getMessage(), var6);
}
}
因为用@ResponseBody不需要返回视图，所以视图那块就返回Null,不需要渲染视图了