springmvc 的请求流程，相信大家已经很熟悉了，不熟悉的同学可以参考下资料！
有了整体流程的概念，是否对其中的实现细节就很清楚呢？我觉得不一定，比如:单是参数解析这块，就是个大学问呢？
首先，我们从最靠近请求末端的地方说起！此时，handler已经找到，即将进行处理！
这是在 RequestMappingHandlerAdapter 的处理方法 handleInternal(), 将请求交给业务代码的地方！
以下是 @ModelAttributeMethodProcessor进行处理的参数处理堆栈:
"http-nio-8080-exec-2@2414" daemon prio=5 tid=0x21 nid=NA runnable java.lang.Thread.State: RUNNABLE at org.springframework.beans.BeanWrapperImpl$BeanPropertyHandler.setValue(BeanWrapperImpl.java:358) at org.springframework.beans.AbstractNestablePropertyAccessor.processLocalProperty(AbstractNestablePropertyAccessor.java:469) at org.springframework.beans.AbstractNestablePropertyAccessor.setPropertyValue(AbstractNestablePropertyAccessor.java:292) at org.springframework.beans.AbstractNestablePropertyAccessor.setPropertyValue(AbstractNestablePropertyAccessor.java:280) at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:95) at org.springframework.validation.DataBinder.applyPropertyValues(DataBinder.java:859) at org.springframework.validation.DataBinder.doBind(DataBinder.java:755) at org.springframework.web.bind.WebDataBinder.doBind(WebDataBinder.java:192) at org.springframework.web.bind.ServletRequestDataBinder.bind(ServletRequestDataBinder.java:106) at org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor.bindRequestParameters(ServletModelAttributeMethodProcessor.java:152) at org.springframework.web.method.annotation.ModelAttributeMethodProcessor.resolveArgument(ModelAttributeMethodProcessor.java:113) at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121) at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:158) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) - locked <0x19d0> (a org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:745)
// org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
@Override
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No synchronization on session demanded at all...
// 更多的时候，我们都是无状态请求的，所以都会走这里，进行业务接入
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
// 然后交给 RequestMappingHandlerAdapter 处理
/**
* Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
* if view resolution is required.
* @since 4.2
* @see #createInvocableHandlerMethod(HandlerMethod)
*/
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
// 将request和response封装为一个类，方便后续使用
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
// 使用 binderFactory 进行参数解析，该 binderFactory 将会伴随整个参数的一生
// 这个binderFactory 与 方法和参数关联
// 然后根据 binderFactory 获取 modelFactory, modelFactory 会绑定一些属性和参数解析器到里面，备用
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
// 创建 最终可用于调用业务方法的包装
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
// 作为返回属性的一个容器
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();
if (logger.isDebugEnabled()) {
logger.debug("Found concurrent result value [" + result + "]");
}
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
// 进一步调用 handler 方法,进入参数解析状态
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) throws Exception {
Class<?> handlerType = handlerMethod.getBeanType();
Set<Method> methods = this.initBinderCache.get(handlerType);
if (methods == null) {
methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS);
this.initBinderCache.put(handlerType, methods);
}
List<InvocableHandlerMethod> initBinderMethods = new ArrayList<InvocableHandlerMethod>();
// Global methods first
for (Entry<ControllerAdviceBean, Set<Method>> entry : this.initBinderAdviceCache.entrySet()) {
if (entry.getKey().isApplicableToBeanType(handlerType)) {
Object bean = entry.getKey().resolveBean();
for (Method method : entry.getValue()) {
initBinderMethods.add(createInitBinderMethod(bean, method));
}
}
}
for (Method method : methods) {
Object bean = handlerMethod.getBean();
initBinderMethods.add(createInitBinderMethod(bean, method));
}
return createDataBinderFactory(initBinderMethods);
}
private ModelFactory getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory) {
SessionAttributesHandler sessionAttrHandler = getSessionAttributesHandler(handlerMethod);
Class<?> handlerType = handlerMethod.getBeanType();
Set<Method> methods = this.modelAttributeCache.get(handlerType);
if (methods == null) {
methods = MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS);
this.modelAttributeCache.put(handlerType, methods);
}
List<InvocableHandlerMethod> attrMethods = new ArrayList<InvocableHandlerMethod>();
// Global methods first
for (Entry<ControllerAdviceBean, Set<Method>> entry : this.modelAttributeAdviceCache.entrySet()) {
if (entry.getKey().isApplicableToBeanType(handlerType)) {
Object bean = entry.getKey().resolveBean();
for (Method method : entry.getValue()) {
attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));
}
}
}
for (Method method : methods) {
Object bean = handlerMethod.getBean();
attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));
}
return new ModelFactory(attrMethods, binderFactory, sessionAttrHandler);
}
// org.springframework.web.method.support.InvocableHandlerMethod
/**
* Invoke the method and handle the return value through one of the
* configured {@link HandlerMethodReturnValueHandler}s.
* @param webRequest the current request
* @param mavContainer the ModelAndViewContainer for this request
* @param providedArgs "given" arguments matched by type (not resolved)
*/
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 此处只处理返回值问题，具体的调用逻辑再封装, 其中 providedArgs 此时仅是空值，将会在后续处理
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
}
else if (StringUtils.hasText(getResponseStatusReason())) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
try {
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex);
}
throw ex;
}
}
以上大体调用流程，下面我们来看下参数解析：
/** * Invoke the method after resolving its argument values in the context of the given request. * <p>Argument values are commonly resolved through {@link HandlerMethodArgumentResolver}s. * The {@code providedArgs} parameter however may supply argument values to be used directly, * i.e. without argument resolution. Examples of provided argument values include a * {@link WebDataBinder}, a {@link SessionStatus}, or a thrown exception instance. * Provided argument values are checked before argument resolvers. * @param request the current request * @param mavContainer the ModelAndViewContainer for this request * @param providedArgs "given" arguments matched by type, not resolved * @return the raw value returned by the invoked method * @exception Exception raised if no suitable argument resolver can be found, * or if the method raised an exception */ public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { // 真正的参数解析在此处开始，是本文关心的点, 此时 providedArgs 还是为空的 Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs); if (logger.isTraceEnabled()) { logger.trace("Invoking '" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) + "' with arguments " + Arrays.toString(args)); } Object returnValue = doInvoke(args); if (logger.isTraceEnabled()) { logger.trace("Method [" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) + "] returned [" + returnValue + "]"); } return returnValue; }
真正的参数解析如下:
/** * Get the method argument values for the current request. */ private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { MethodParameter[] parameters = getMethodParameters(); Object[] args = new Object[parameters.length]; for (int i = 0; i < parameters.length; i++) { MethodParameter parameter = parameters[i]; parameter.initParameterNameDiscovery(this.parameterNameDiscoverer); args[i] = resolveProvidedArgument(parameter, providedArgs); if (args[i] != null) { continue; } // 依次遍历解析器，只要有一个支持解析，则进行解析逻辑，否则抛出异常 if (this.argumentResolvers.supportsParameter(parameter)) { try { // 进行具体解析器的解析，当然，这里是解析器列表，调用后会再进行合适解析器的筛选过程 args[i] = this.argumentResolvers.resolveArgument( parameter, mavContainer, request, this.dataBinderFactory); continue; } catch (Exception ex) { if (logger.isDebugEnabled()) { logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex); } throw ex; } } if (args[i] == null) { throw new IllegalStateException("Could not resolve method parameter at index " + parameter.getParameterIndex() + " in " + parameter.getMethod().toGenericString() + ": " + getArgumentResolutionErrorMessage("No suitable resolver for", i)); } } return args; }
可以看出，参数解析主要分为几步:
1. 获取参数类型数组,供后续填充使用;
2. 对每个参数类型，单独调用参数解析过程;
3. 在进行具体解析之前，先尝试简单解析是否成功(类似于读取缓存)，不成功则再进行深度解析;
4. 深度解析交由所有解析器进行处理, 即 HandlerMethodArgumentResolverComposite, 它包含了所有的解析器;
// org.springframework.web.method.support.HandlerMethodArgumentResolverComposite /** * Iterate over registered {@link HandlerMethodArgumentResolver}s and invoke the one that supports it. * @throws IllegalStateException if no suitable {@link HandlerMethodArgumentResolver} is found. */ @Override public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception { // 获取具体适用的解析器，即调用其 supportsParameter(param) 方法判断即可 HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter); if (resolver == null) { throw new IllegalArgumentException("Unknown parameter type [" + parameter.getParameterType().getName() + "]"); } // 解析器获取到后，就交由具体的解析器进行解析了，这里有很多的分支了，咱们可以挑选几个来看一下就可以了 return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory); }
下面，我我们看一下 @ModelAttribute 修饰的参数解析方法(注意: 这里的解析只是针对任意一个参数的解析，所以无需关注整体参数形式):
// org.springframework.web.method.annotation.ModelAttributeMethodProcessor /** * Resolve the argument from the model or if not found instantiate it with * its default if it is available. The model attribute is then populated * with request values via data binding and optionally validated * if {@code @java.validation.Valid} is present on the argument. * @throws BindException if data binding and validation result in an error * and the next method parameter is not of type {@link Errors}. * @throws Exception if WebDataBinder initialization fails. */ @Override public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception { // 获取参数名字, 如: User user 获取的结果为 user ; 其实现原理为获取该注解的 value 值 // 如果缓存中没有该参数的解析,那么就实例化一个参数实例，并放入缓存 String name = ModelFactory.getNameForParameter(parameter); Object attribute = (mavContainer.containsAttribute(name) ? mavContainer.getModel().get(name) : createAttribute(name, parameter, binderFactory, webRequest)); if (!mavContainer.isBindingDisabled(name)) { ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class); if (ann != null && !ann.binding()) { mavContainer.setBindingDisabled(name); } } // 将参数包装进 WebDataBinder 中，方便统一操作, 将参数实例放入到 target 字段域中 WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name); if (binder.getTarget() != null) { // 进行参数的解析过程, 将由 ServletModelAttributeMethodProcessor 处理 if (!mavContainer.isBindingDisabled(name)) { bindRequestParameters(binder, webRequest); } validateIfApplicable(binder, parameter); if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) { throw new BindException(binder.getBindingResult()); } } // Add resolved attribute and BindingResult at the end of the model Map<String, Object> bindingResultModel = binder.getBindingResult().getModel(); mavContainer.removeAttributes(bindingResultModel); mavContainer.addAllAttributes(bindingResultModel); return binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter); } // 如下为获取参数名的实现方式,如果指明 value, 则直接获取, 否则生成一个参数简称名的字段, 注意此处的名字并不一定是 参数真正的命名 // 其实函数的调用只要参数位置正确即可，并不需要真实的变量名 public static String getNameForParameter(MethodParameter parameter) { ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class); String name = (ann != null ? ann.value() : null); return (StringUtils.hasText(name) ? name : Conventions.getVariableNameForParameter(parameter)); } // org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor /** * This implementation downcasts {@link WebDataBinder} to * {@link ServletRequestDataBinder} before binding. * @see ServletRequestDataBinderFactory */ @Override protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) { // 取出request 对象，因为只有 request 中有需要处理的参数,此时和 response 是确认无关的 ServletRequest servletRequest = request.getNativeRequest(ServletRequest.class); ServletRequestDataBinder servletBinder = (ServletRequestDataBinder) binder; // 调用自身的 binder 处理 servletBinder.bind(servletRequest); } /** * Bind the parameters of the given request to this binder's target, * also binding multipart files in case of a multipart request. * <p>This call can create field errors, representing basic binding * errors like a required field (code "required"), or type mismatch * between value and bean property (code "typeMismatch"). * <p>Multipart files are bound via their parameter name, just like normal * HTTP parameters: i.e. "uploadedFile" to an "uploadedFile" bean property, * invoking a "setUploadedFile" setter method. * <p>The type of the target property for a multipart file can be MultipartFile, * byte[], or String. The latter two receive the contents of the uploaded file; * all metadata like original file name, content type, etc are lost in those cases. * @param request request with parameters to bind (can be multipart) * @see org.springframework.web.multipart.MultipartHttpServletRequest * @see org.springframework.web.multipart.MultipartFile * @see #bind(org.springframework.beans.PropertyValues) */ public void bind(ServletRequest request) { // 将所有请求参数封装到 mpvs, 使后续可以直接获取, 其实现为 使用 ArrayList 来保存属性，参考: request.getParameterNames() MutablePropertyValues mpvs = new ServletRequestParameterPropertyValues(request); MultipartRequest multipartRequest = WebUtils.getNativeRequest(request, MultipartRequest.class); if (multipartRequest != null) { bindMultipart(multipartRequest.getMultiFileMap(), mpvs); } // 此处作为扩展点，预留 addBindValues(mpvs, request); // 调用webDataBinder 设值到参数绑定 doBind(mpvs); } // org.springframework.web.bind.WebDataBinder /** * This implementation performs a field default and marker check * before delegating to the superclass binding process. * @see #checkFieldDefaults * @see #checkFieldMarkers */ @Override protected void doBind(MutablePropertyValues mpvs) { // 检查默认值和 marker 设置 checkFieldDefaults(mpvs); checkFieldMarkers(mpvs); // 调用父类实现数据 绑定，其实就是反射调用字段 super.doBind(mpvs); } // DataBinder.doBind() /** * Actual implementation of the binding process, working with the * passed-in MutablePropertyValues instance. * @param mpvs the property values to bind, * as MutablePropertyValues instance * @see #checkAllowedFields * @see #checkRequiredFields * @see #applyPropertyValues */ protected void doBind(MutablePropertyValues mpvs) { checkAllowedFields(mpvs); checkRequiredFields(mpvs); // 处理值 applyPropertyValues(mpvs); } /** * Apply given property values to the target object. * <p>Default implementation applies all of the supplied property * values as bean property values. By default, unknown fields will * be ignored. * @param mpvs the property values to be bound (can be modified) * @see #getTarget * @see #getPropertyAccessor * @see #isIgnoreUnknownFields * @see #getBindingErrorProcessor * @see BindingErrorProcessor#processPropertyAccessException */ protected void applyPropertyValues(MutablePropertyValues mpvs) { try { // Bind request parameters onto target object. getPropertyAccessor().setPropertyValues(mpvs, isIgnoreUnknownFields(), isIgnoreInvalidFields()); } catch (PropertyBatchUpdateException ex) { // Use bind error processor to create FieldErrors. for (PropertyAccessException pae : ex.getPropertyAccessExceptions()) { getBindingErrorProcessor().processPropertyAccessException(pae, getInternalBindingResult()); } } } @Override public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid) throws BeansException { List<PropertyAccessException> propertyAccessExceptions = null; // 此处获取参数对象的n个字段为列表,以进行循环赋值, 即循环的依据是外部传入多少值,而不是参数实例有多少字段 List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ? ((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues())); // 多个参数值给定时，循环设值即可 for (PropertyValue pv : propertyValues) { try { // This method may throw any BeansException, which won't be caught // here, if there is a critical failure such as no matching field. // We can attempt to deal only with less serious exceptions. // 对单个 field 设值 setPropertyValue(pv); } catch (NotWritablePropertyException ex) { if (!ignoreUnknown) { throw ex; } // Otherwise, just ignore it and continue... } catch (NullValueInNestedPathException ex) { if (!ignoreInvalid) { throw ex; } // Otherwise, just ignore it and continue... } catch (PropertyAccessException ex) { if (propertyAccessExceptions == null) { propertyAccessExceptions = new LinkedList<PropertyAccessException>(); } propertyAccessExceptions.add(ex); } } // org.springframework.beans.AbstractNestablePropertyAccessor @Override public void setPropertyValue(PropertyValue pv) throws BeansException { PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens; if (tokens == null) { String propertyName = pv.getName(); AbstractNestablePropertyAccessor nestedPa; try { nestedPa = getPropertyAccessorForPropertyPath(propertyName); } catch (NotReadablePropertyException ex) { throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName, "Nested property in path '" + propertyName + "' does not exist", ex); } tokens = getPropertyNameTokens(getFinalPath(nestedPa, propertyName)); if (nestedPa == this) { pv.getOriginalPropertyValue().resolvedTokens = tokens; } nestedPa.setPropertyValue(tokens, pv); } else { setPropertyValue(tokens, pv); } } // 对字段特殊处理，否则直接设值 protected void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException { if (tokens.keys != null) { processKeyedProperty(tokens, pv); } else { processLocalProperty(tokens, pv); } } private void processLocalProperty(PropertyTokenHolder tokens, PropertyValue pv) { PropertyHandler ph = getLocalPropertyHandler(tokens.actualName); if (ph == null || !ph.isWritable()) { if (pv.isOptional()) { if (logger.isDebugEnabled()) { logger.debug("Ignoring optional value for property '" + tokens.actualName + "' - property not found on bean class [" + getRootClass().getName() + "]"); } return; } else { throw createNotWritablePropertyException(tokens.canonicalName); } } Object oldValue = null; try { Object originalValue = pv.getValue(); Object valueToApply = originalValue; if (!Boolean.FALSE.equals(pv.conversionNecessary)) { if (pv.isConverted()) { valueToApply = pv.getConvertedValue(); } else { if (isExtractOldValueForEditor() && ph.isReadable()) { try { oldValue = ph.getValue(); } catch (Exception ex) { if (ex instanceof PrivilegedActionException) { ex = ((PrivilegedActionException) ex).getException(); } if (logger.isDebugEnabled()) { logger.debug("Could not read previous value of property '" + this.nestedPath + tokens.canonicalName + "'", ex); } } } valueToApply = convertForProperty( tokens.canonicalName, oldValue, originalValue, ph.toTypeDescriptor()); } pv.getOriginalPropertyValue().conversionNecessary = (valueToApply != originalValue); } // 经过各种判定后，终于调用反射了 ph.setValue(this.wrappedObject, valueToApply); } catch (TypeMismatchException ex) { throw ex; } catch (InvocationTargetException ex) { PropertyChangeEvent propertyChangeEvent = new PropertyChangeEvent( this.rootObject, this.nestedPath + tokens.canonicalName, oldValue, pv.getValue()); if (ex.getTargetException() instanceof ClassCastException) { throw new TypeMismatchException(propertyChangeEvent, ph.getPropertyType(), ex.getTargetException()); } else { Throwable cause = ex.getTargetException(); if (cause instanceof UndeclaredThrowableException) { // May happen e.g. with Groovy-generated methods cause = cause.getCause(); } throw new MethodInvocationException(propertyChangeEvent, cause); } } catch (Exception ex) { PropertyChangeEvent pce = new PropertyChangeEvent( this.rootObject, this.nestedPath + tokens.canonicalName, oldValue, pv.getValue()); throw new MethodInvocationException(pce, ex); } } // org.springframework.beans.BeanWrapperImpl$BeanPropertyHandler @Override public void setValue(final Object object, Object valueToApply) throws Exception { final Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ? ((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() : this.pd.getWriteMethod()); if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) { if (System.getSecurityManager() != null) { AccessController.doPrivileged(new PrivilegedAction<Object>() { @Override public Object run() { writeMethod.setAccessible(true); return null; } }); } else { writeMethod.setAccessible(true); } } final Object value = valueToApply; if (System.getSecurityManager() != null) { try { AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { @Override public Object run() throws Exception { writeMethod.invoke(object, value); return null; } }, acc); } catch (PrivilegedActionException ex) { throw ex.getException(); } } else { // java.lang.reflect.Method, 反射设值 writeMethod.invoke(getWrappedInstance(), value); } }
所以，对于 @ModelAttribute 参数解析,其实主要有几步:
1. 获取 request 中的参数，封装到 MutablePropertyValues 中;
2. 依次检查每个字段域的有效性;
3. 处理字段类型的转换,如:将 String 转换为 int;
4. 获取字段的反射方法,进行字段值的绑定;
5. 循环设置,直到所有字段都检查完;
6. 验证字段的有效性,如有异常，抛出;
7. 做最后的数据类型确认，如果进一步处理，则转换;(conversionService)
// 验证字段有效性，如有必要的话, 以 Valid* 开头即符合验证前提
/**
* Validate the model attribute if applicable.
* <p>The default implementation checks for {@code @javax.validation.Valid},
* Spring's {@link org.springframework.validation.annotation.Validated},
* and custom annotations whose name starts with "Valid".
* @param binder the DataBinder to be used
* @param methodParam the method parameter
*/
protected void validateIfApplicable(WebDataBinder binder, MethodParameter methodParam) {
Annotation[] annotations = methodParam.getParameterAnnotations();
for (Annotation ann : annotations) {
Validated validatedAnn = AnnotationUtils.getAnnotation(ann, Validated.class);
// 只要以 Valid 打头的验证都可以，即做到 spring 自身的验证方式有效，但是也兼容其他框架的验证方式
if (validatedAnn != null || ann.annotationType().getSimpleName().startsWith("Valid")) {
Object hints = (validatedAnn != null ? validatedAnn.value() : AnnotationUtils.getValue(ann));
Object[] validationHints = (hints instanceof Object[] ? (Object[]) hints : new Object[] {hints});
// 调用验证方式，一般为 调用其 validate() 方法;
binder.validate(validationHints);
break;
}
}
}
/**
* Invoke the specified Validators, if any, with the given validation hints.
* <p>Note: Validation hints may get ignored by the actual target Validator.
* @param validationHints one or more hint objects to be passed to a {@link SmartValidator}
* @see #setValidator(Validator)
* @see SmartValidator#validate(Object, Errors, Object...)
*/
public void validate(Object... validationHints) {
for (Validator validator : getValidators()) {
if (!ObjectUtils.isEmpty(validationHints) && validator instanceof SmartValidator) {
((SmartValidator) validator).validate(getTarget(), getBindingResult(), validationHints);
}
else if (validator != null) {
validator.validate(getTarget(), getBindingResult());
}
}
}
// 转换堆栈如下: "http-nio-8080-exec-6@2418" daemon prio=5 tid=0x25 nid=NA runnable java.lang.Thread.State: RUNNABLE at org.springframework.core.convert.support.GenericConversionService.handleResult(GenericConversionService.java:328) at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:204) at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:173) at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:108) at org.springframework.beans.TypeConverterSupport.doConvert(TypeConverterSupport.java:64) at org.springframework.beans.TypeConverterSupport.convertIfNecessary(TypeConverterSupport.java:47) at org.springframework.validation.DataBinder.convertIfNecessary(DataBinder.java:713) at org.springframework.web.method.annotation.ModelAttributeMethodProcessor.resolveArgument(ModelAttributeMethodProcessor.java:126) at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121) at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:158) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) - locked <0x2028> (a org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:745)
/** * Convert the value to the required type (if necessary from a String), * for the specified property. * @param propertyName name of the property * @param oldValue the previous value, if available (may be {@code null}) * @param newValue the proposed new value * @param requiredType the type we must convert to * (or {@code null} if not known, for example in case of a collection element) * @param typeDescriptor the descriptor for the target property or field * @return the new value, possibly the result of type conversion * @throws IllegalArgumentException if type conversion failed */ @SuppressWarnings("unchecked") public <T> T convertIfNecessary(String propertyName, Object oldValue, Object newValue, Class<T> requiredType, TypeDescriptor typeDescriptor) throws IllegalArgumentException { // Custom editor for this type? PropertyEditor editor = this.propertyEditorRegistry.findCustomEditor(requiredType, propertyName); ConversionFailedException conversionAttemptEx = null; // No custom editor but custom ConversionService specified? ConversionService conversionService = this.propertyEditorRegistry.getConversionService(); if (editor == null && conversionService != null && newValue != null && typeDescriptor != null) { TypeDescriptor sourceTypeDesc = TypeDescriptor.forObject(newValue); if (conversionService.canConvert(sourceTypeDesc, typeDescriptor)) { try { return (T) conversionService.convert(newValue, sourceTypeDesc, typeDescriptor); } catch (ConversionFailedException ex) { // fallback to default conversion logic below conversionAttemptEx = ex; } } } Object convertedValue = newValue; // Value not of required type? if (editor != null || (requiredType != null && !ClassUtils.isAssignableValue(requiredType, convertedValue))) { if (typeDescriptor != null && requiredType != null && Collection.class.isAssignableFrom(requiredType) && convertedValue instanceof String) { TypeDescriptor elementTypeDesc = typeDescriptor.getElementTypeDescriptor(); if (elementTypeDesc != null) { Class<?> elementType = elementTypeDesc.getType(); if (Class.class == elementType || Enum.class.isAssignableFrom(elementType)) { convertedValue = StringUtils.commaDelimitedListToStringArray((String) convertedValue); } } } if (editor == null) { editor = findDefaultEditor(requiredType); } convertedValue = doConvertValue(oldValue, convertedValue, requiredType, editor); } boolean standardConversion = false; if (requiredType != null) { // Try to apply some standard type conversion rules if appropriate. if (convertedValue != null) { if (Object.class == requiredType) { return (T) convertedValue; } else if (requiredType.isArray()) { // Array required -> apply appropriate conversion of elements. if (convertedValue instanceof String && Enum.class.isAssignableFrom(requiredType.getComponentType())) { convertedValue = StringUtils.commaDelimitedListToStringArray((String) convertedValue); } return (T) convertToTypedArray(convertedValue, propertyName, requiredType.getComponentType()); } else if (convertedValue instanceof Collection) { // Convert elements to target type, if determined. convertedValue = convertToTypedCollection( (Collection<?>) convertedValue, propertyName, requiredType, typeDescriptor); standardConversion = true; } else if (convertedValue instanceof Map) { // Convert keys and values to respective target type, if determined. convertedValue = convertToTypedMap( (Map<?, ?>) convertedValue, propertyName, requiredType, typeDescriptor); standardConversion = true; } if (convertedValue.getClass().isArray() && Array.getLength(convertedValue) == 1) { convertedValue = Array.get(convertedValue, 0); standardConversion = true; } if (String.class == requiredType && ClassUtils.isPrimitiveOrWrapper(convertedValue.getClass())) { // We can stringify any primitive value... return (T) convertedValue.toString(); } else if (convertedValue instanceof String && !requiredType.isInstance(convertedValue)) { if (conversionAttemptEx == null && !requiredType.isInterface() && !requiredType.isEnum()) { try { Constructor<T> strCtor = requiredType.getConstructor(String.class); return BeanUtils.instantiateClass(strCtor, convertedValue); } catch (NoSuchMethodException ex) { // proceed with field lookup if (logger.isTraceEnabled()) { logger.trace("No String constructor found on type [" + requiredType.getName() + "]", ex); } } catch (Exception ex) { if (logger.isDebugEnabled()) { logger.debug("Construction via String failed for type [" + requiredType.getName() + "]", ex); } } } String trimmedValue = ((String) convertedValue).trim(); if (requiredType.isEnum() && "".equals(trimmedValue)) { // It's an empty enum identifier: reset the enum value to null. return null; } convertedValue = attemptToConvertStringToEnum(requiredType, trimmedValue, convertedValue); standardConversion = true; } else if (convertedValue instanceof Number && Number.class.isAssignableFrom(requiredType)) { convertedValue = NumberUtils.convertNumberToTargetClass( (Number) convertedValue, (Class<Number>) requiredType); standardConversion = true; } } else { // convertedValue == null if (javaUtilOptionalEmpty != null && requiredType == javaUtilOptionalEmpty.getClass()) { convertedValue = javaUtilOptionalEmpty; } } if (!ClassUtils.isAssignableValue(requiredType, convertedValue)) { if (conversionAttemptEx != null) { // Original exception from former ConversionService call above... throw conversionAttemptEx; } else if (conversionService != null) { // ConversionService not tried before, probably custom editor found // but editor couldn't produce the required type... TypeDescriptor sourceTypeDesc = TypeDescriptor.forObject(newValue); if (conversionService.canConvert(sourceTypeDesc, typeDescriptor)) { return (T) conversionService.convert(newValue, sourceTypeDesc, typeDescriptor); } } // Definitely doesn't match: throw IllegalArgumentException/IllegalStateException StringBuilder msg = new StringBuilder(); msg.append("Cannot convert value of type '").append(ClassUtils.getDescriptiveType(newValue)); msg.append("' to required type '").append(ClassUtils.getQualifiedName(requiredType)).append("'"); if (propertyName != null) { msg.append(" for property '").append(propertyName).append("'"); } if (editor != null) { msg.append(": PropertyEditor [").append(editor.getClass().getName()).append( "] returned inappropriate value of type '").append( ClassUtils.getDescriptiveType(convertedValue)).append("'"); throw new IllegalArgumentException(msg.toString()); } else { msg.append(": no matching editors or conversion strategy found"); throw new IllegalStateException(msg.toString()); } } } if (conversionAttemptEx != null) { if (editor == null && !standardConversion && requiredType != null && Object.class != requiredType) { throw conversionAttemptEx; } logger.debug("Original ConversionService attempt failed - ignored since " + "PropertyEditor based conversion eventually succeeded", conversionAttemptEx); } return (T) convertedValue; }
以上是 @ModelAttribute 的参数解析, 下面我们再来看两个常用的类型解析:
1. @RequestParam 解析, 解析普通的变量;
2. @RequestBody 解析, 解析 json 的请求;
@RequestParam 的参数解析, 从 HandlerMethodArgumentResolverComposite -> RequestParamMethodArgumentResolver :
// org.springframework.web.method.annotation.RequestParamMethodArgumentResolver
// org/springframework/web/method/annotation/AbstractNamedValueMethodArgumentResolver
@Override
public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
// 使用 NamedValueInfo 来封装参数,
NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);
MethodParameter nestedParameter = parameter.nestedIfOptional();
// 变量名称替换 比如将 ${a} 替换为 a; 这里会经过一层 BeanExpressionResolver 的解析处理
Object resolvedName = resolveStringValue(namedValueInfo.name);
if (resolvedName == null) {
throw new IllegalArgumentException(
"Specified name must not resolve to null: [" + namedValueInfo.name + "]");
}
// 根据参数名, 获取该值,该方法为 子类的扩展点,即由 RequestParamMethodArgumentResolver 处理
Object arg = resolveName(resolvedName.toString(), nestedParameter, webRequest);
if (arg == null) {
if (namedValueInfo.defaultValue != null) {
arg = resolveStringValue(namedValueInfo.defaultValue);
}
else if (namedValueInfo.required && !nestedParameter.isOptional()) {
handleMissingValue(namedValueInfo.name, nestedParameter, webRequest);
}
arg = handleNullValue(namedValueInfo.name, arg, nestedParameter.getNestedParameterType());
}
else if ("".equals(arg) && namedValueInfo.defaultValue != null) {
arg = resolveStringValue(namedValueInfo.defaultValue);
}
if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
try {
// 进行类型转换切入点处理, 由于前面返回的参数是 String 类型的，所以，类型的转换必然交给此处处理
arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter);
}
catch (ConversionNotSupportedException ex) {
throw new MethodArgumentConversionNotSupportedException(arg, ex.getRequiredType(),
namedValueInfo.name, parameter, ex.getCause());
}
catch (TypeMismatchException ex) {
throw new MethodArgumentTypeMismatchException(arg, ex.getRequiredType(),
namedValueInfo.name, parameter, ex.getCause());
}
}
// 再一个预留扩展点，供用户自定义再次处理结果，默认为空
handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest);
return arg;
}
/**
* Obtain the named value for the given method parameter.
*/
private NamedValueInfo getNamedValueInfo(MethodParameter parameter) {
NamedValueInfo namedValueInfo = this.namedValueInfoCache.get(parameter);
if (namedValueInfo == null) {
namedValueInfo = createNamedValueInfo(parameter);
namedValueInfo = updateNamedValueInfo(parameter, namedValueInfo);
this.namedValueInfoCache.put(parameter, namedValueInfo);
}
return namedValueInfo;
}
// RequestParamMethodArgumentResolver, 进行创建 NamedValueInfo
@Override
protected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {
RequestParam ann = parameter.getParameterAnnotation(RequestParam.class);
return (ann != null ? new RequestParamNamedValueInfo(ann) : new RequestParamNamedValueInfo());
}
/**
* Resolve the given annotation-specified value,
* potentially containing placeholders and expressions.
*/
private Object resolveStringValue(String value) {
if (this.configurableBeanFactory == null) {
return value;
}
String placeholdersResolved = this.configurableBeanFactory.resolveEmbeddedValue(value);
BeanExpressionResolver exprResolver = this.configurableBeanFactory.getBeanExpressionResolver();
if (exprResolver == null) {
return value;
}
return exprResolver.evaluate(placeholdersResolved, this.expressionContext);
}
// RequestParamMethodArgumentResolver
@Override
protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {
HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);
MultipartHttpServletRequest multipartRequest =
WebUtils.getNativeRequest(servletRequest, MultipartHttpServletRequest.class);
Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);
if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
return mpArg;
}
Object arg = null;
if (multipartRequest != null) {
List<MultipartFile> files = multipartRequest.getFiles(name);
if (!files.isEmpty()) {
arg = (files.size() == 1 ? files.get(0) : files);
}
}
if (arg == null) {
// 此处允许传入数组长度的为n的参数，但是只会取第一个参数使用, 而且返回值都是 String 类型
String[] paramValues = request.getParameterValues(name);
if (paramValues != null) {
arg = (paramValues.length == 1 ? paramValues[0] : paramValues);
}
}
return arg;
}
总结下 @RequestParam 的处理过程:
1. 由于 RequestParam 的处理方式简单，直接继承父类操作 resolveArgument();
2. 使用 namedValueInfo 来封装请求参数, 一般只针对简单类型的参数操作;
3. 解析定义的 变量名称,可支持 ${xxx} 这样的 expr 表达式处理;
4. 根据变量名称,从request中获取参数，返回第一个值作为参数的原始值;
5. 经过一些类型转换操作,如果需要的话;
6. 值设置完成后，预留一个扩展点给用户;
其实，简单说 @RequestParam 的处理就是，直接 获取 request 中对应的变量值即可;
下面，我们来看一个复杂点的参数解析: @RequestBody 的解析;
起点当然还是 HandlerMethodArgumentResolverComposite.resolveArgument() 了;
// org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor
/**
* Throws MethodArgumentNotValidException if validation fails.
* @throws HttpMessageNotReadableException if {@link RequestBody#required()}
* is {@code true} and there is no body content or if there is no suitable
* converter to read the content with.
*/
@Override
public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
// 先检查可选选循环嵌套数情况
parameter = parameter.nestedIfOptional();
// 使用消息转换器进行接收参数,因为 对json的解析，不像其他参数解析一样套路只有一个，这个是有大量数据的解析，应该把这个选择权交给用户
// 比如默认使用 jackson 来解析, 但是往往其效率并不高，而用户则可以选择像 fastjson 这样的组件来处理
Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());
String name = Conventions.getVariableNameForParameter(parameter);
WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
if (arg != null) {
validateIfApplicable(binder, parameter);
if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
}
}
mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
return adaptArgumentIfNecessary(arg, parameter);
}
@Override
protected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter parameter,
Type paramType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(servletRequest);
// 调用父类解析方法
Object arg = readWithMessageConverters(inputMessage, parameter, paramType);
if (arg == null) {
if (checkRequired(parameter)) {
throw new HttpMessageNotReadableException("Required request body is missing: " +
parameter.getMethod().toGenericString());
}
}
return arg;
}
// org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver
/**
* Create the method argument value of the expected parameter type by reading
* from the given HttpInputMessage.
* @param <T> the expected type of the argument value to be created
* @param inputMessage the HTTP input message representing the current request
* @param parameter the method parameter descriptor (may be {@code null})
* @param targetType the target type, not necessarily the same as the method
* parameter type, e.g. for {@code HttpEntity<String>}.
* @return the created method argument value
* @throws IOException if the reading from the request fails
* @throws HttpMediaTypeNotSupportedException if no suitable message converter is found
*/
@SuppressWarnings("unchecked")
protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter parameter,
Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
// Content-Type: application/json
MediaType contentType;
boolean noContentType = false;
try {
contentType = inputMessage.getHeaders().getContentType();
}
catch (InvalidMediaTypeException ex) {
throw new HttpMediaTypeNotSupportedException(ex.getMessage());
}
if (contentType == null) {
noContentType = true;
contentType = MediaType.APPLICATION_OCTET_STREAM;
}
Class<?> contextClass = (parameter != null ? parameter.getContainingClass() : null);
Class<T> targetClass = (targetType instanceof Class ? (Class<T>) targetType : null);
if (targetClass == null) {
ResolvableType resolvableType = (parameter != null ?
ResolvableType.forMethodParameter(parameter) : ResolvableType.forType(targetType));
targetClass = (Class<T>) resolvableType.resolve();
}
HttpMethod httpMethod = ((HttpRequest) inputMessage).getMethod();
Object body = NO_VALUE;
try {
// 通过获取 inputMessage.getBody(); 并封装为 EmptyBodyCheckingHttpInputMessage
inputMessage = new EmptyBodyCheckingHttpInputMessage(inputMessage);
// 循环调用 消息转换器, 依次处理
for (HttpMessageConverter<?> converter : this.messageConverters) {
Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
if (converter instanceof GenericHttpMessageConverter) {
// fastjson 走这里
GenericHttpMessageConverter<?> genericConverter = (GenericHttpMessageConverter<?>) converter;
if (genericConverter.canRead(targetType, contextClass, contentType)) {
if (logger.isDebugEnabled()) {
logger.debug("Read [" + targetType + "] as "" + contentType + "" with [" + converter + "]");
}
if (inputMessage.getBody() != null) {
inputMessage = getAdvice().beforeBodyRead(inputMessage, parameter, targetType, converterType);
body = genericConverter.read(targetType, contextClass, inputMessage);
body = getAdvice().afterBodyRead(body, inputMessage, parameter, targetType, converterType);
}
else {
body = getAdvice().handleEmptyBody(null, inputMessage, parameter, targetType, converterType);
}
break;
}
}
else if (targetClass != null) {
// 调用转换器的 canRead() 方法，判断是否可处理该类型的数据，由这郸城 接入 json 转换器
// 当然，这里在公共抽象类中会有一个封装, return supports(clazz) && canRead(mediaType); 可以重写这两个方法
// 在springmvc中，不定义 json 转换器将导致报错
if (converter.canRead(targetClass, contentType)) {
if (logger.isDebugEnabled()) {
logger.debug("Read [" + targetType + "] as "" + contentType + "" with [" + converter + "]");
}
// 做消息转换的切点埋入
if (inputMessage.getBody() != null) {
inputMessage = getAdvice().beforeBodyRead(inputMessage, parameter, targetType, converterType);
body = ((HttpMessageConverter<T>) converter).read(targetClass, inputMessage);
body = getAdvice().afterBodyRead(body, inputMessage, parameter, targetType, converterType);
}
else {
body = getAdvice().handleEmptyBody(null, inputMessage, parameter, targetType, converterType);
}
break;
}
}
}
}
catch (IOException ex) {
throw new HttpMessageNotReadableException("I/O error while reading input message", ex);
}
if (body == NO_VALUE) {
if (httpMethod == null || !SUPPORTED_METHODS.contains(httpMethod) ||
(noContentType && inputMessage.getBody() == null)) {
return null;
}
throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);
}
return body;
}
// 内部类 EmptyBodyCheckingHttpInputMessage 如下
private static class EmptyBodyCheckingHttpInputMessage implements HttpInputMessage {
private final HttpHeaders headers;
private final InputStream body;
private final HttpMethod method;
public EmptyBodyCheckingHttpInputMessage(HttpInputMessage inputMessage) throws IOException {
this.headers = inputMessage.getHeaders();
InputStream inputStream = inputMessage.getBody();
if (inputStream == null) {
this.body = null;
}
else if (inputStream.markSupported()) {
inputStream.mark(1);
this.body = (inputStream.read() != -1 ? inputStream : null);
inputStream.reset();
}
else {
// 检测是否有数据，没有则设置为 null
PushbackInputStream pushbackInputStream = new PushbackInputStream(inputStream);
int b = pushbackInputStream.read();
if (b == -1) {
this.body = null;
}
else {
this.body = pushbackInputStream;
pushbackInputStream.unread(b);
}
}
this.method = ((HttpRequest) inputMessage).getMethod();
}
@Override
public HttpHeaders getHeaders() {
return this.headers;
}
@Override
public InputStream getBody() throws IOException {
return this.body;
}
public HttpMethod getMethod() {
return this.method;
}
}
这里我们使用 fastjson 的转换器来看一下json的转换吧; FastJsonHttpMessageConverter.read()
由于 FastJsonHttpMessageConverter 是一个 GenericHttpMessageConverter, 所以会走第一个通用逻辑.
// com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter
public boolean canRead(Type type, Class<?> contextClass, MediaType mediaType) {
return super.canRead(contextClass, mediaType);
}
@Override
protected boolean supports(Class<?> clazz) {
// 交由 canRead() 统一控制
return true;
}
/**
* Returns {@code true} if any of the {@linkplain #setSupportedMediaTypes(List)
* supported} media types {@link MediaType#includes(MediaType) include} the
* given media type.
* @param mediaType the media type to read, can be {@code null} if not specified.
* Typically the value of a {@code Content-Type} header.
* @return {@code true} if the supported media types include the media type,
* or if the media type is {@code null}
*/
protected boolean canRead(MediaType mediaType) {
// 没有 application/json 的设置也是支持的哦
if (mediaType == null) {
return true;
}
for (MediaType supportedMediaType : getSupportedMediaTypes()) {
if (supportedMediaType.includes(mediaType)) {
return true;
}
}
return false;
}
// 而其 read() 方法,则是比较简洁的，直接调用 fastjson 的 parseObject() 方法即可;
/*
* @see org.springframework.http.converter.GenericHttpMessageConverter#read(java.lang.reflect.Type, java.lang.Class, org.springframework.http.HttpInputMessage)
*/
public Object read(Type type, //
Class<?> contextClass, //
HttpInputMessage inputMessage //
) throws IOException, HttpMessageNotReadableException {
InputStream in = inputMessage.getBody();
return JSON.parseObject(in, fastJsonConfig.getCharset(), type, fastJsonConfig.getFeatures());
}
好了，我们来总结下 json 的转换方式吧！
1. 检查循环嵌套问题;
2. 将消息体封装进 EmptyBodyCheckingHttpInputMessage 中;
3. 获取配置好的转换器，其中必须要有 json 转换器，否则将报错;
4. 调用配置json转换器，进行格式验证;
5. 进行消息转换，转换逻辑与spring就没什么关系了;(如果有兴趣查看json的转换逻辑可以参考fastjson源码)
这里一个关键的步骤是，配置一个json转换器! 这里给出一个最简单的配置方式:
<mvc:annotation-driven> <mvc:message-converters register-defaults="true"> <bean id="fastJsonHttpMessageConverter" class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter"> <property name="supportedMediaTypes"> <list> <value>application/json;charset=UTF-8</value> </list> </property> </bean> </mvc:message-converters> </mvc:annotation-driven>
仅此足够！