[Feign] 如何處理非 2xx 的響應? 如何獲取 Header ?

在構建微服務的過程中, 我們時常會需要藉助 Spring Cloud Open Feign 組件調用第三方依賴服務. 有時, 被依賴的服務使用 RESTful 實現接口, 而調用方需要處理非 2xx 狀態的請求. 這個時候, 問題來了.

嘗試使用 ResponseEntity

熟悉 Spring MVC 的同學可能會想到 ResponseEntity 這個類, 並嘗試定義類似以下形式的 api:

@FeignClient
public class Dependency {

	@RequestMapping
	org.springframework.http.ResponseEntity<Object> maybeOk();
}	

然後再這樣使用:

ResponseEntity<Object> response = dependency.maybeOk();
if (!response.getStatusCode().is2xxSuccessful()) {
	// do something A
} else {
    // do something B
}

但實際上, 當依賴服務返回的狀態碼不是 2xx 時, 業務代碼塊 A 會因爲無法處理 FeignException 而不會被執行.

[404 NOT FOUND] during [GET] to [https://httpbin.org/status/404] [Dependency#maybeOk()]: []
feign.FeignException$NotFound: [404 NOT FOUND] during [GET] to [https://httpbin.org/status/404] [Dependency#maybeOk()]: []
	at feign.FeignException.clientErrorStatus(FeignException.java:201)
	at feign.FeignException.errorStatus(FeignException.java:177)
	at feign.FeignException.errorStatus(FeignException.java:169)
	at feign.codec.ErrorDecoder$Default.decode(ErrorDecoder.java:92)
	at feign.AsyncResponseHandler.handleResponse(AsyncResponseHandler.java:96) // 關鍵類 AsyncResponseHandler
	at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:138)
	at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:89)
	at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:100)
	at dev.dengchao.$Proxy180.maybeOk(Unknown Source)
	at dev.dengchao.FeignTests.test(FeignTests.java:39)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)

分析 AsyncResponseHandler

根據異常日誌, 反向分析異常出現的原因, 可以在 AsyncResponseHandler#handleResponse() 方法中有所發現:

void handleResponse(CompletableFuture<Object> resultFuture,
                      String configKey,
                      Response response,
                      Type returnType,
                      long elapsedTime) {
    // copied fairly liberally from SynchronousMethodHandler
    boolean shouldClose = true;
    try {
      if (logLevel != Level.NONE) {
        response = logger.logAndRebufferResponse(configKey, logLevel, response,
            elapsedTime);
      }
      if (Response.class == returnType) {
        if (response.body() == null) {
          resultFuture.complete(response);
        } else if (response.body().length() == null
            || response.body().length() > MAX_RESPONSE_BUFFER_SIZE) {
          shouldClose = false;
          resultFuture.complete(response);
        } else {
          // Ensure the response body is disconnected
          final byte[] bodyData = Util.toByteArray(response.body().asInputStream());
          resultFuture.complete(response.toBuilder().body(bodyData).build());
        }
      } else if (response.status() >= 200 && response.status() < 300) {
        if (isVoidType(returnType)) {
          resultFuture.complete(null);
        } else {
          final Object result = decode(response, returnType);
          shouldClose = closeAfterDecode;
          resultFuture.complete(result);
        }
      } else if (decode404 && response.status() == 404 && !isVoidType(returnType)) {
        final Object result = decode(response, returnType);
        shouldClose = closeAfterDecode;
        resultFuture.complete(result);
      } else {
        resultFuture.completeExceptionally(errorDecoder.decode(configKey, response)); // 上面拋出異常的地方
      }
    } catch (final IOException e) {
      if (logLevel != Level.NONE) {
        logger.logIOException(configKey, logLevel, e, elapsedTime);
      }
      resultFuture.completeExceptionally(errorReading(response.request(), response, e));
    } catch (final Exception e) {
      resultFuture.completeExceptionally(e);
    } finally {
      if (shouldClose) {
        ensureClosed(response.body());
      }
    }
  }

通過分析, 我們可以得知由於 maybeOk() 方法返回值類型不是 Response, 狀態碼非 2xx, 並且默認沒有對 404 狀態解碼, 從而觸發了異常.

使用 feign.Response 來處理非 2xx 響應, 獲取 Header

分析出異常產生的原因後, 解法也就一目瞭然了. 將 maybeOk 方法的返回值類型修改爲 Response :

@FeignClient
public class Dependency {

	@RequestMapping
	feign.Response<Object> maybeOk();
}	

然後再這樣使用:

Response response = dependency.maybeOk();
if (response.status() != 200) {
	// do something A
} else {
	Map<String, Collection<String>> headers = response.headers();
    // do something B
}

這樣, 業務代碼塊 A 就能正常的在依賴服務返回非 200 狀態時被調用了.

參考

• Spring framework @GitHub
• Spring Cloud Open Feign @GitHub
• Open Feign @GitHub
• Feign REST Client: How to get the HTTP status? @StackOverflow

備註

演示代碼是基於 Spring Cloud Hoxton SR6 與 Spring boot 2.2.8.RELEASE 相關類庫進行展示的, 如有出入, 請自行分析.

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import feign.FeignException;
import feign.Response;
import lombok.Data;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;

import java.io.IOException;
import java.util.Map;

@Slf4j
@SpringBootTest
public class FeignTests {
    @Autowired
    HttpBinService service;
    @Autowired
    ObjectMapper mapper;

    @Test
    void test() throws IOException {
        Response response = service.ok();
        Assertions.assertEquals(HttpStatus.OK.value(), response.status());
        Ip ip = mapper.readValue(response.body().asInputStream(), Ip.class);
        log.info("{}", ip);

        Assertions.assertEquals(HttpStatus.NOT_FOUND.value(), service.notFound().status());

        try {
            service.maybeOk();
        } catch (Exception e) {
            Assertions.assertTrue(e instanceof FeignException);
            Assertions.assertEquals(HttpStatus.NOT_FOUND.value(), ((FeignException) e).status());
        }
    }

    @FeignClient(value = "http-bin", url = "https://httpbin.org")
    interface HttpBinService {

        @GetMapping("/ip")
        Response ok();

        @GetMapping("/status/404")
        Response notFound();

        @GetMapping("/status/404")
        ResponseEntity<Object> maybeOk();
    }

    @Data
    static class Ip {
        private String origin;
    }
}