1、解决的问题

加了@ResponseBody注解的方法，请求的方式是post的json格式，但如果我们也要通过post的application/x-www-form-urlencoded格式访问此接口。在不改变此接口的情况下。通过修改参数解析器HandlerMethodArgumentResovler来兼容两种请求方法。

2、思路

根据不同的content-type使用不同参数解析处理器。
Content-Type为application/x-www-form-urlencoded，使用ServletModelAttributeMethodProcessor解析器
Content-Type非application/x-www-form-urlencoded，使用RequestResponseBodyMethodProcessor解析器

3、代码实现

定义自己的参数解析器，继承HandlerMethodArgumentResolver

/**
 * 自定义参数解析器
 * 功能:实现不同类型参数的解析
 * 使用@RequestBody注解，Content-Type为application/x-www-form-urlencoded，使用ServletModelAttributeMethodProcessor解析器
 * 使用@RequestBody注解，Content-Type非application/x-www-form-urlencoded，使用RequestResponseBodyMethodProcessor解析器
 *
 * @author lilei
 * @since 2020/05/09
 */
@Log4j
public class CustomMethodArgumentResolver implements HandlerMethodArgumentResolver {

  private RequestResponseBodyMethodProcessor requestResponseBodyMethodProcessor;

  private ServletModelAttributeMethodProcessor servletModelAttributeMethodProcessor;

  private final String APPLICATION_X_WWW_FORM_URLENCODED = "application/x-www-form-urlencoded";

  private final String MULTIPART_FORM_DATA = "multipart/form-data";

  public CustomMethodArgumentResolver(
      RequestResponseBodyMethodProcessor requestResponseBodyMethodProcessor,
      ServletModelAttributeMethodProcessor servletModelAttributeMethodProcessor) {
    this.requestResponseBodyMethodProcessor = requestResponseBodyMethodProcessor;
    this.servletModelAttributeMethodProcessor = servletModelAttributeMethodProcessor;
  }

  /**
   *  参数解析器适用参数条件
   *
   * @param methodParameter
   * @return 使用@RequestBody注解 返回true，未使用返回false
   * @tips 可以使用自定义注解
   */
  @Override
  public boolean supportsParameter(MethodParameter methodParameter) {
    return methodParameter.hasParameterAnnotation(RequestBody.class);
  }

  /**
   * 参数解析
   * @param methodParameter
   * @param modelAndViewContainer
   * @param nativeWebRequest
   * @param webDataBinderFactory
   * @return
   * @throws Exception
   */
  @Override
  public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {
    HttpServletRequest request = nativeWebRequest.getNativeRequest(HttpServletRequest.class);
    if (request == null) {
      throw new CustomrException(JsonResultCode.CODE_REQUEST_NULL.getName());
    }
    String contentType = request.getContentType();
    //更加请求contentType不同使用不同解析器
    log.info("contentType:"+contentType);
    if (contentType.contains(APPLICATION_X_WWW_FORM_URLENCODED)||contentType.contains(MULTIPART_FORM_DATA)) {
      log.info("Processor:"+servletModelAttributeMethodProcessor);
      return servletModelAttributeMethodProcessor.resolveArgument(methodParameter, modelAndViewContainer, nativeWebRequest, webDataBinderFactory);
    }
    log.info("Processor:"+requestResponseBodyMethodProcessor);
    return requestResponseBodyMethodProcessor.resolveArgument(methodParameter, modelAndViewContainer, nativeWebRequest, webDataBinderFactory);
  }
}

注册参数解析器

/**
 * 配置注册参数解析器
 */
@Configuration
@Log4j
public class ResolverConfig {

  private final RequestMappingHandlerAdapter requestMappingHandlerAdapter;

  public ResolverConfig(RequestMappingHandlerAdapter requestMappingHandlerAdapter) {
    this.requestMappingHandlerAdapter = requestMappingHandlerAdapter;
  }

  @PostConstruct
  private void addArgumentResolvers() {
    log.info("start add argument resolvers...");
    // 获取到的是不可变的集合
    List<HandlerMethodArgumentResolver> argumentResolvers = requestMappingHandlerAdapter.getArgumentResolvers();
CustomMethodArgumentResolver customMethodArgumentResolver = getCustomMethodArgumentResolver(argumentResolvers);
    //新建参数解析器列表，然后将新列表添加到requestMappingHandlerAdapter中
    List<HandlerMethodArgumentResolver> newArgumentResolverList = new ArrayList<>(argumentResolvers.size() + 1);
    // 将自定义方法参数解析器放置在第一个，并保留原来的解析器
    newArgumentResolverList.add(customMethodArgumentResolver );
    newArgumentResolverList.addAll(argumentResolvers);
    requestMappingHandlerAdapter.setArgumentResolvers(newArgumentResolverList);
    log.info("add argument resolvers end!!!");
  }

  /**
   * 获取自定义方法参数解析器
   * @param argumentResolversList
   * @return
   */
  private CustomMethodArgumentResolver getCustomMethodArgumentResolver(List<HandlerMethodArgumentResolver> argumentResolversList) {
    // 解析Content-Type为application/json的默认解析器
    RequestResponseBodyMethodProcessor requestResponseBodyMethodProcessor = null;
    // 解析Content-Type为application/x-www-form-urlencoded的默认解析器
    ServletModelAttributeMethodProcessor servletModelAttributeMethodProcessor = null;

    if (argumentResolversList == null) {
      throw new CustomResolverException(JsonResultCode.CODE_RESOLVER_NULL.getName(),JsonResultCode.CODE_RESOLVER_NULL.getCode());
    }
    for (HandlerMethodArgumentResolver argumentResolver : argumentResolversList) {
      if (requestResponseBodyMethodProcessor != null && servletModelAttributeMethodProcessor != null) {
        break;
      }
      if (argumentResolver instanceof RequestResponseBodyMethodProcessor) {
        requestResponseBodyMethodProcessor = (RequestResponseBodyMethodProcessor) argumentResolver;
        continue;
      }
      if (argumentResolver instanceof ServletModelAttributeMethodProcessor) {
        servletModelAttributeMethodProcessor = (ServletModelAttributeMethodProcessor) argumentResolver;
      }
    }
    if (requestResponseBodyMethodProcessor == null || servletModelAttributeMethodProcessor == null) {
      throw new CustomResolverException(JsonResultCode.CODE_RESOLVER_VALUE_NULL.getName(),JsonResultCode.CODE_RESOLVER_VALUE_NULL.getCode());
    }
    return new CustomMethodArgumentResolver(requestResponseBodyMethodProcessor, servletModelAttributeMethodProcessor);
  }
}