场景：很多时候可能我们需要调用第三方平台,例如OSS、alipay或者是未在注册中心注册的服务，通常我们可以选用RestTemplate来操作，但是有时候我们更想通过Feign的方式来直接调用远程的接口。

public interface DispatchCodeFeign {
  @RequestLine(value = "POST /dispatchcode/fetchCodes")
  @Headers("Content-Type: application/json")
  DispatchCodeResult<Map<String, DispatchCodeVo>> fetchCodes(URI baseUri, @RequestBody List<DisPatchCodeDto> disPatchCodeDtos);
}

参数说明：

@ReqeustLine:相当于WebMvc中的@RequestMapping

@Headers: 请求头

1.baseUri：需要调用的地址路径

2.disPatchCodeDto：具体的参数

此处为什么不直接使用FeignClient(url="${动态配置}")？

因为在Spring的加载顺序 会先加载FeignClient再去加载apollo的配置，所以url不能解析到动态配置的属性，只能通过Feign原生api的方式来进行动态的传入uri。

@Configuration
public class OmsApiFeignConfig {
  /**请求连接超时时间1S**/
  private final int CONNECT_TIME_OUT = 1000;
  /**请求读取超时时间10S**/
  private final int READ_TIME_OUT = 10000;
  /**feign command**/
  private final String FEIGN_COMMAND = "dispatchCode";

  @Bean
  public DispatchCodeFeign dispatchCodeFeign(Decoder decoder, Encoder encoder, DispatchCodeFallBack fallback) {
    Target<DispatchCodeFeign> target = Target.EmptyTarget.create(DispatchCodeFeign.class, FEIGN_COMMAND);
    HystrixFeign.Builder builder = HystrixFeign.builder();
    DispatchCodeFeign orderReportFeign = builder
            .options(new Request.Options(CONNECT_TIME_OUT, READ_TIME_OUT))
            .encoder(encoder)
            .decoder(decoder)
            .target(target, fallback);
    return orderReportFeign;
  }
}

需要引用此feign的Service 需要加入注解 @Import(FeignClientsConfiguration.class)

@Service
@Slf4j
@Import(FeignClientsConfiguration.class)
public class DispatchCodeServiceImpl extends AbstractCacheServiceImpl implements IDispatchCodeService {
  @Value("${dispatch.code.uri:\"\"}")
  private String dispatchCodeUri;

  private URI uri = null;

  private final Integer RES_FAIL = 0;

  @Autowired
  private DispatchCodeFeign dispatchCodeFeign;

  @Override
  public DispatchCodeVo fetch(DisPatchCodeDto disPatchCodeDto) {
    URI uri = getUri();

    Long startTime = System.currentTimeMillis();
    log.info("【请求三段码】地址:{},入参: {}", uri, JSONUtil.toJsonStr(disPatchCodeDto));
    DispatchCodeResult<Map<String, DispatchCodeVo>> result = dispatchCodeFeign.fetchCodes(uri, Arrays.asList(disPatchCodeDto));
    log.info("【请求三段码】耗时:{},返回值: {}", System.currentTimeMillis() - startTime, JSONUtil.toJsonStr(result));
    //请求成功
    if (isSuccess(result) && Objects.nonNull(result.getData()) && result.getData().containsKey(disPatchCodeDto.getUniqueSequence())) {
      return result.getData().get(disPatchCodeDto.getUniqueSequence());
    }
    return null;
  }

  private <T> boolean isSuccess(DispatchCodeResult<T> dispatchCodeResult) {
    if (Objects.isNull(dispatchCodeResult)) {
      return false;
    }
    if (RES_FAIL.equals(dispatchCodeResult.getCode())) {
      return false;
    }
    return true;
  }

  private URI getUri() {
    if (Objects.isNull(uri) || !dispatchCodeUri.equals(uri.toString())) {
      synchronized (DispatchCodeServiceImpl.class) {
        if (Objects.isNull(uri) || !dispatchCodeUri.equals(uri.toString())) {
          try {
            uri = new URI(dispatchCodeUri);
          } catch (Exception e) {
            log.error("【创建uri发生异常】异常信息: {}", e);
            throw new ServiceException(ResultCodeEnum.FAIL);
          }
        }
      }
    }
    return uri;
  }
}