springMVC源碼分析--HttpMessageConverter參數read操做（二）

時間 2019-11-13

標籤 springmvc 源碼分析 httpmessageconverter 參數 read 欄目 Spring 简体版

原文原文鏈接

上一篇博客 springMVC源碼分析--HttpMessageConverter數據轉化（一）中咱們簡單介紹了一下HttpMessageConverter接口提供的幾個方法，主要有如下幾個方法：web

（1）canRead 是否能夠讀spring

（2）canWrite 是否能夠寫app

（3）read() 讀數據ide

（4）write() 寫數據源碼分析

接下來咱們介紹一下讀取數據的處理操做。ui

首先要去重溫一下參數處理器須要作的操做springMVC源碼分析--RequestParamMethodArgumentResolver參數解析器（三），AbstractNamedValueMethodArgumentResolver中的resolveArgument方法，解析參數值this

public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
           NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
       .......
       Object arg = resolveName(namedValueInfo.name, parameter, webRequest);
       ......
   }
簡單的提交數據的示例：.net

@RequestMapping(value="/save")
public String saveProduct( String name,@RequestBody String description,@RequestBody float price, Model model)
.......
}
咱們能夠在HandlerMethodArgumentResolver的子類RequestResponseBodyMethodProcessor的方法resolveArgument看到以下處理，這裏就是對提交的參數的處理debug

public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
           NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

       Object arg = readWithMessageConverters(webRequest, parameter, parameter.getGenericParameterType());
       .........
   }
接下來在readWithMessageConverters中的處理以下：orm

@Override
   protected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter methodParam,
           Type paramType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
       HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
       ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(servletRequest);
       Object arg = readWithMessageConverters(inputMessage, methodParam, paramType);
       if (arg == null) {
           if (methodParam.getParameterAnnotation(RequestBody.class).required()) {
               throw new HttpMessageNotReadableException("Required request body is missing: " +
                       methodParam.getMethod().toGenericString());
           }
       }
       return arg;
   }
在父類AbstractMessageConverterMethodArgumentResolver的方法readWithMessageConverters中的處理以下：簡單來講就是根據提供的實現的HttpMessageConverter來對提交的RequestBody中的數據進行轉換處理。
@SuppressWarnings("unchecked")
   protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter param,
           Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
       //獲取數據類型
       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 = (param != null ? param.getContainingClass() : null);
       Class<T> targetClass = (targetType instanceof Class<?> ? (Class<T>) targetType : null);
       if (targetClass == null) {
           ResolvableType resolvableType = (param != null ?
                   ResolvableType.forMethodParameter(param) : ResolvableType.forType(targetType));
           targetClass = (Class<T>) resolvableType.resolve();
       }

       HttpMethod httpMethod = ((HttpRequest) inputMessage).getMethod();
       Object body = NO_VALUE;

       try {
           inputMessage = new EmptyBodyCheckingHttpInputMessage(inputMessage);
           //選擇適合的消息處理器來處理參數
           for (HttpMessageConverter<?> converter : this.messageConverters) {
               Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
               //判斷是否適合處理參數
               if (converter instanceof GenericHttpMessageConverter) {
                   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, param, targetType, converterType);
                           //處理參數
                           body = genericConverter.read(targetType, contextClass, inputMessage);
                           body = getAdvice().afterBodyRead(body, inputMessage, param, targetType, converterType);
                       }
                       else {
                           body = null;
                           body = getAdvice().handleEmptyBody(body, inputMessage, param, targetType, converterType);
                       }
                       break;
                   }
               }
               else if (targetClass != null) {
                   if (converter.canRead(targetClass, contentType)) {
                       if (logger.isDebugEnabled()) {
                           logger.debug("Read [" + targetType + "] as \"" + contentType + "\" with [" + converter + "]");
                       }
                       if (inputMessage.getBody() != null) {
                           inputMessage = getAdvice().beforeBodyRead(inputMessage, param, targetType, converterType);
                           //處理數據，對於簡單的String數據使用StringHttpMessageConverter進行處理
                           body = ((HttpMessageConverter<T>) converter).read(targetClass, inputMessage);
                           body = getAdvice().afterBodyRead(body, inputMessage, param, targetType, converterType);
                       }
                       else {
                           body = null;
                           body = getAdvice().handleEmptyBody(body, inputMessage, param, targetType, converterType);
                       }
                       break;
                   }
               }
           }
       }
       catch (IOException ex) {
           throw new HttpMessageNotReadableException("Could not read document: " + ex.getMessage(), ex);
       }

       if (body == NO_VALUE) {
           if (httpMethod == null || !SUPPORTED_METHODS.contains(httpMethod) ||
                   (noContentType && inputMessage.getBody() == null)) {
               return null;
           }
           throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);
       }
       //最終返回處理的結果值
       return body;
   }
springMVC默認提供了不少參數和結果值處理器，包括以下：