IllegalArgumentException：使用Spring自定义参数解析器时参数类型不匹配

Question

public final class SpringArgumentResolver implements HandlerMethodArgumentResolver {

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return CommonHeader.class.isAssignableFrom(parameter.getParameterType());
    }

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

        CommonHeader commonHeader = new CommonHeader();

        String user_id = webRequest.getHeader("UserID");
       
        commonHeader.setUser_id(user_id);

            return commonHeader;
    }

@Configuration
@EnableWebMvc
public class SpringWebMvcConfig implements WebMvcConfigurer {


    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
        resolvers.add(new SpringArgumentResolver());
    }

}

public class CommonHeader {

    private String user_id;
    private String ip_address;
    private String request_id;

    public CommonHeader(String user_id) {
            this.user_id = user_id;
    }
    public CommonHeader(){}
 
    public String getUser_id() {
        return user_id;
    }

    public void setUser_id(String user_id) {
        this.user_id = user_id;
    }
}

@GetMapping("user_data")
public DeferredResult<ResponseEntity<JsonNode>> getUserPreferenceData(GetDataRequest getDataRequest) {
            DeferredResult<ResponseEntity<JsonNode>> deferredResult = new DeferredResult<>();
         // some logic 
        //  some logic
       return deferredResult;
    }

@Getter
@Setter
public class GetDataRequest extends CommonHeader {

    private String name1;
    private String name2;
   
}

Answer 1

您的SpringArgumentResolver错误。GetDataRequest是CommonHeader，但CommonHeader不是GetDataRequest。您的SpringArgumentResolver总是返回一个CommonDataHeader，该CommonDataHeader，不能转换成GetDataRequest，因此出现错误。

CommonHeader header = new CommonHeader();
GetDataRequest request = (GetDataRequest) header;

基本上就是你所期望的会自动发生的事情。现在，这在常规java中不起作用（导致ClassCastException)，为什么在Spring中要起作用呢？Spring会检查结果对象是否可以分配给该方法参数，在本例中是因为getDataRequest.isAssignableFrom（commonheader.class）；将返回false（尽管相反是true！）。

在SpringArgumentResolver中应该做的是动态确定类并实例化它，将其强制转换为CommonHeader并设置字段。

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

    CommonHeader commonHeader = BeanUtils.instantiateClass(parameter.getParameterType());
    String user_id = webRequest.getHeader("UserID");
    commonHeader.setUser_id(user_id);
    return commonHeader;
}