spring-webmvc-4.3.19.RELEASE
下面来看DispatcherServlet中的执行：
/**
* Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
* for the actual dispatching.
*/
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
" processing " + request.getMethod() + " request for [" + getRequestUri(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<String, Object>();
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.
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());
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);
try {
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);
}
}
}
}
org.springframework.web.servlet.DispatcherServlet#doService
/**
* Process the actual dispatching to the handler.
* <p>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.
* <p>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 {
processedRequest = checkMultipart(request);//文件上传处理解析器
multipartRequestParsed = (processedRequest != request);//是否文件上传请求
// Determine handler for the current request. 获取匹配的HandlerExecutionChain
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
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;
}
}//todo:确认下这个代码块是不是为了处理etag?
//执行拦截器的applyPreHandle，如果返回false，则流程直接结束
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler. 执行处理器，返回mav
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);//如果视图为空，给予设置默认视图的名称
mappedHandler.applyPostHandle(processedRequest, response, mv); //执行处理器拦截器的applyPostHandle
}
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);
}
//处理请求结果。显然，此时请求已经结束【也是@ControlAdvice生效的地方】
//如果是逻辑视图【MVC场景有指定的模板需要渲染或页面需要跳转】，则解析名称；否则，就不解析
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 {
//释放资源
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);//执行拦截器的方法
}
}
else {
// Clean up any resources used by a multipart request. 文件请求资源释放
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
org.springframework.web.servlet.DispatcherServlet#doDispatch
首先看下doDispatch()方法如何找到适合的适配器来执行方法的：
/**
* Return the HandlerAdapter for this handler object.
* @param handler the handler object to find an adapter for
* @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
*/
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
for (HandlerAdapter ha : this.handlerAdapters) {
if (logger.isTraceEnabled()) {
logger.trace("Testing handler adapter [" + ha + "]");
}
if (ha.supports(handler)) {
return ha;
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
org.springframework.web.servlet.DispatcherServlet#getHandlerAdapter
0 = {RequestMappingHandlerAdapter@11772}
1 = {HttpRequestHandlerAdapter@11773}
2 = {SimpleControllerHandlerAdapter@11774}
【0】 RequestMappingHandlerAdapter 【org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter】：
/**
* Provides a method for invoking the handler method for a given request after resolving its
* method argument values through registered {@link HandlerMethodArgumentResolver}s.
*
* <p>Argument resolution often requires a {@link WebDataBinder} for data binding or for type
* conversion. Use the {@link #setDataBinderFactory(WebDataBinderFactory)} property to supply
* a binder factory to pass to argument resolvers.
*
* <p>Use {@link #setHandlerMethodArgumentResolvers} to customize the list of argument resolvers.
*
* @author Rossen Stoyanchev
* @author Juergen Hoeller
* @since 3.1
*/
public class InvocableHandlerMethod extends HandlerMethod {
/**
* An {@link AbstractHandlerMethodAdapter} that supports {@link HandlerMethod}s
* with their method argument and return type signature, as defined via
* {@code @RequestMapping}.
*
* <p>Support for custom argument and return value types can be added via
* {@link #setCustomArgumentResolvers} and {@link #setCustomReturnValueHandlers}.
* Or alternatively, to re-configure all argument and return value types,
* use {@link #setArgumentResolvers} and {@link #setReturnValueHandlers}.
*
* @author Rossen Stoyanchev
* @author Juergen Hoeller
* @since 3.1
* @see HandlerMethodArgumentResolver
* @see HandlerMethodReturnValueHandler
*/
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
【org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter#supports】
/**
* This implementation expects the handler to be an {@link HandlerMethod}.
* @param handler the handler instance to check
* @return whether or not this adapter can adapt the given handler
*/
@Override
public final boolean supports(Object handler) {
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}
/**
* Extends {@link InvocableHandlerMethod} with the ability to handle return
* values through a registered {@link HandlerMethodReturnValueHandler} and
* also supports setting the response status based on a method-level
* {@code @ResponseStatus} annotation.
*
* <p>A {@code null} return value (including void) may be interpreted as the
* end of request processing in combination with a {@code @ResponseStatus}
* annotation, a not-modified check condition
* (see {@link ServletWebRequest#checkNotModified(long)}), or
* a method argument that provides access to the response stream.
*
* @author Rossen Stoyanchev
* @author Juergen Hoeller
* @since 3.1
*/
public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
private static final Method CALLABLE_METHOD = ClassUtils.getMethod(Callable.class, "call");
((ApplicationContextFacade) ((ServletContextResource) resource).getServletContext()).context.getContext().getDocBase()：
docBase ： C:\Users\TANGCH~1\AppData\Local\Temp\tomcat-docbase.8903617127552296966.8080
C:\Users\TANGCH~1\AppData\Local\Temp\tomcat-docbase.8903617127552296966.8080
/**
* Records model and view related decisions made by
* {@link HandlerMethodArgumentResolver}s and
* {@link HandlerMethodReturnValueHandler}s during the course of invocation of
* a controller method.
*
* <p>The {@link #setRequestHandled} flag can be used to indicate the request
* has been handled directly and view resolution is not required.
*
* <p>A default {@link Model} is automatically created at instantiation.
* An alternate model instance may be provided via {@link #setRedirectModel}
* for use in a redirect scenario. When {@link #setRedirectModelScenario} is set
* to {@code true} signalling a redirect scenario, the {@link #getModel()}
* returns the redirect model instead of the default model.
*
* @author Rossen Stoyanchev
* @author Juergen Hoeller
* @since 3.1
*/
public class ModelAndViewContainer {
【1】 HttpRequestHandlerAdapter 【org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter】
/**
* Adapter to use the plain {@link org.springframework.web.HttpRequestHandler}
* interface with the generic {@link org.springframework.web.servlet.DispatcherServlet}.
* Supports handlers that implement the {@link LastModified} interface.
*
* <p>This is an SPI class, not used directly by application code.
*
* @author Juergen Hoeller
* @since 2.0
* @see org.springframework.web.servlet.DispatcherServlet
* @see org.springframework.web.HttpRequestHandler
* @see LastModified
* @see SimpleControllerHandlerAdapter
*/
public class HttpRequestHandlerAdapter implements HandlerAdapter {
@Override
public boolean supports(Object handler) {
return (handler instanceof HttpRequestHandler);
}
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
/**
* This implementation expects the handler to be an {@link HandlerMethod}.
* @param handler the handler instance to check
* @return whether or not this adapter can adapt the given handler
*/
@Override
public final boolean supports(Object handler) {
return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));//延迟做决定，由子类来决定相关的逻辑
}
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter#supports
【org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter】
/**
* Always return {@code true} since any method argument and return value
* type will be processed in some way. A method argument not recognized
* by any HandlerMethodArgumentResolver is interpreted as a request parameter
* if it is a simple type, or as a model attribute otherwise. A return value
* not recognized by any HandlerMethodReturnValueHandler will be interpreted
* as a model attribute.
*/
@Override
protected boolean supportsInternal(HandlerMethod handlerMethod) {
return true;
}
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#supportsInternal
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。
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()[0];
asyncManager.clearConcurrentResult();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Found concurrent result value [" + result + "]");
}
requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);
}
requestMappingMethod.invokeAndHandle(webRequest, mavContainer, new Object[0]); //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 = 0; 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
/**
* Whether the given {@linkplain MethodParameter method parameter} is
* supported by this resolver.
* @param parameter the method parameter to check
* @return {@code true} if this resolver supports the supplied parameter;
* {@code false} otherwise
org.springframework.web.method.support.HandlerMethodArgumentResolver#supportsParameter
*/
@Override
public boolean supportsParameter(MethodParameter parameter) {
return parameter.hasParameterAnnotation(RequestBody.class);
}
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor#supportsParameter
/**
* Whether the given {@linkplain MethodParameter method return type} is
* supported by this handler.
* @param returnType the method return type to check
* @return {@code true} if this handler supports the supplied return type;
* {@code false} otherwise
org.springframework.web.method.support.HandlerMethodReturnValueHandler#supportsReturnType
*/
@Override
public boolean supportsReturnType(MethodParameter returnType) {
return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class) ||
returnType.hasMethodAnnotation(ResponseBody.class));
}
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor#supportsReturnType
/**
* Handle the given return value by adding attributes to the model and
* setting a view or setting the
* {@link ModelAndViewContainer#setRequestHandled} flag to {@code true}
* to indicate the response has been handled directly.
* @param returnValue the value returned from the handler method
* @param returnType the type of the return value. This type must have
* previously been passed to {@link #supportsReturnType} which must
* have returned {@code true}.
* @param mavContainer the ModelAndViewContainer for the current request
* @param webRequest the current request
* @throws Exception if the return value handling results in an error
org.springframework.web.method.support.HandlerMethodReturnValueHandler#handleReturnValue
*/
@Override
public void handleReturnValue(Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
mavContainer.setRequestHandled(true);
ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);
// Try even with null return value. ResponseBodyAdvice could get involved.
writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);//用内置的消息转换器来转换结果集
}
org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor#handleReturnValue
下面来看是怎么寻找可以合适的消息转换器的
/**
* Writes the given return type to the given output message.
* @param value the value to write to the output message
* @param returnType the type of the value
* @param inputMessage the input messages. Used to inspect the {@code Accept} header.
* @param outputMessage the output message to write to
* @throws IOException thrown in case of I/O errors
* @throws HttpMediaTypeNotAcceptableException thrown when the conditions indicated
* by the {@code Accept} header on the request cannot be met by the message converters
*/
@SuppressWarnings("unchecked")
protected <T> void writeWithMessageConverters(T value, MethodParameter returnType,
ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
Object outputValue;
Class<?> valueType;
Type declaredType;
if (value instanceof CharSequence) {
outputValue = value.toString();
valueType = String.class;
declaredType = String.class;
}
else {
outputValue = value;
valueType = getReturnValueType(outputValue, returnType);
declaredType = getGenericType(returnType);
}
HttpServletRequest request = inputMessage.getServletRequest();
List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(request);//获取请求的MediaType,eg："application/json"
List<MediaType> producibleMediaTypes = getProducibleMediaTypes(request, valueType, declaredType);//寻找支持这个返回类型的转换器支持的MediaType
if (outputValue != null && producibleMediaTypes.isEmpty()) {
throw new IllegalArgumentException("No converter found for return value of type: " + valueType);
}
//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？？
Set<MediaType> compatibleMediaTypes = new LinkedHashSet<MediaType>();
for (MediaType requestedType : requestedMediaTypes) {
for (MediaType producibleType : producibleMediaTypes) {
if (requestedType.isCompatibleWith(producibleType)) {
compatibleMediaTypes.add(getMostSpecificMediaType(requestedType, producibleType));
}
}
}
if (compatibleMediaTypes.isEmpty()) {
if (outputValue != null) {
throw new HttpMediaTypeNotAcceptableException(producibleMediaTypes);
}
return;
}
List<MediaType> mediaTypes = new ArrayList<MediaType>(compatibleMediaTypes);
MediaType.sortBySpecificityAndQuality(mediaTypes);
MediaType selectedMediaType = null;
for (MediaType mediaType : mediaTypes) {
if (mediaType.isConcrete()) {
selectedMediaType = mediaType;
break;
}
else if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION)) {
selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
break;
}
}
if (selectedMediaType != null) {
selectedMediaType = selectedMediaType.removeQualityValue();
for (HttpMessageConverter<?> messageConverter : this.messageConverters) {
//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。
if (messageConverter instanceof GenericHttpMessageConverter) {
if (((GenericHttpMessageConverter) messageConverter).canWrite(
declaredType, valueType, selectedMediaType)) {
outputValue = (T) getAdvice().beforeBodyWrite(outputValue, returnType, selectedMediaType,
(Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(),
inputMessage, outputMessage);
if (outputValue != null) {
addContentDispositionHeader(inputMessage, outputMessage);
((GenericHttpMessageConverter) messageConverter).write(
outputValue, declaredType, selectedMediaType, outputMessage);
if (logger.isDebugEnabled()) {
logger.debug("Written [" + outputValue + "] as \"" + selectedMediaType +
"\" using [" + messageConverter + "]");
}
}
return;
}
}
else if (messageConverter.canWrite(valueType, selectedMediaType)) {
outputValue = (T) getAdvice().beforeBodyWrite(outputValue, returnType, selectedMediaType,
(Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(),
inputMessage, outputMessage);
if (outputValue != null) {
addContentDispositionHeader(inputMessage, outputMessage);
((HttpMessageConverter) messageConverter).write(outputValue, selectedMediaType, outputMessage);
if (logger.isDebugEnabled()) {
logger.debug("Written [" + outputValue + "] as \"" + selectedMediaType +
"\" using [" + messageConverter + "]");
}
}
return;
}
}
}
if (outputValue != null) {
throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes);
}
}
org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor#writeWithMessageConverters(T, org.springframework.core.MethodParameter, org.springframework.http.server.ServletServerHttpRequest, org.springframework.http.server.ServletServerHttpResponse)
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)) {
return true;
}
for (MediaType supportedMediaType : getSupportedMediaTypes()) {//获取子类解析器支持的MediaType，看下是否支持
if (supportedMediaType.isCompatibleWith(mediaType)) {
return true;
}
}
return false;
}
org.springframework.http.converter.AbstractHttpMessageConverter#canWrite(org.springframework.http.MediaType)
write方法 父类也帮着实现了，父类具体做了如输出，拼输出流头等信息
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
