SpringCloud OpenFeign 自定义响应解码器的问题记录

public class JsonResult<T> {
    /* 响应码，200为成功   */
    private Integer code;
    /* 失败时的具体失败信息   */
    private String message;
    /* 成功时的数据对象   */
    private T data;
}
 

@FeignClient(
    name = "xxx-base", 
    path = "/api/base",
    configuration = CustomizedConfiguration.class /* 自定义配置类 */
)
public interface RemoteUserService {
    //..
}

public class CustomizedConfiguration{
    @Bean
    public Decoder feignDecoder() {
        return new OpenFeignResultDecoder();
    }
}

public class OpenFeignResultDecoder implements Decoder {
    @Resource
    ObjectMapper objectMapper;
    @Override
    public Object decode(Response response, Type type) throws IOException, DecodeException, FeignException {
        String resultJson = this.getResponseBody(response);
        try {
            JavaType rawType = objectMapper.getTypeFactory().constructType(type);
            JavaType resultType = objectMapper.getTypeFactory().constructParametricType(JsonResult.class, rawType.getRawClass());
            JsonResult<?> jsonResult = objectMapper.readValue(resultJson, resultType );
            if (jsonResult.getCode() != HttpStatus.OK.value()){
                throw new DecodeException(
                        response.status(),
                        jsonResult.getMessage(),
                        response.request());
            }
            return jsonResult.getData();
        } catch (Exception ex){
            throw new IllegalArgumentException("对象转换失败: " + ex.getMessage());
        }
    }
    /* 
     * 将 response body 解析为 string 
     */ 
    private static String getResponseBody(Response response) throws IOException {
        Response.Body resBody = response.body();
        if (Objects.isNull(resBody)){
            throw new DecodeException(
                    response.status(),
                    "返回体为空",
                    response.request());
        }
        String jsonStr;
        char[] buffer = new char[1024*4];
        int len;
        try (
                Reader reader = resBody.asReader(StandardCharsets.UTF_8);
                StringWriter strWriter = new StringWriter()
        ){
            while ((len = reader.read(buffer)) != -1){
                strWriter.write(buffer, 0, len);
            }
            jsonStr= strWriter.toString();
        }
        return jsonStr;
    }
}

@Configuration
public class OpenFeignConfig {
    @Bean
    public Decoder feignDecoder() {
        return new OpenFeignResultDecoder();
    }
}

@FeignClient(
    name = "xxx-base",
    path = "/api/base"
)
public interface RemoteUserService {
    //..
}

@FeignClient(
    name = "xxx-base",
    path = "/api/base"
)
public interface RemoteUserService {
   @GetMapping(value = "/user/detail/{userId}")
   public User getUserDetailById(@PathVariable Integer userId)
}

// ...
@Resource
RemouteUserService userService
public void demoUserService(int userId){
    User user = userService.getUserDetailById(userId);
    // ....
}