Spring Cloud Feign(第四篇)之Fallback
Spring Cloud Feign 之Fallback
環境資訊: java 1.8、Spring boot 1.5.10.RELEASE、spring cloud-Edgware.SR3、maven 3.3+
在網路請求時，可能會出現異常請求，如果還想再異常情況下使系統可用，那麼就需要容錯處理，比如:網路請求超時時給使用者提示“稍後重試”或使用本地快照資料等等。
Spring Cloud Feign就是通過Fallback實現的，有兩種方式：
1、@FeignClient.fallback = UserFeignFallback.class指定一個實現Feign介面的實現類。
2、@FeignClient.fallbackFactory = UserFeignFactory.class指定一個實現FallbackFactory<T>工廠介面類
因為Fallback是通過Hystrix實現的， 所以需要開啟Hystrix，spring boot application.properties檔案配置feign.hystrix.enabled=true，這樣就開啟了Fallback
Fallback-實現Feign介面
UserFeignFallback回撥實現，由spring建立使用@Component(其他的註冊也可以)註解
HystrixTargeter.targetWithFallback方法實現了@FeignClient.fallback處理邏輯，通過原始碼可以知道UserFeignFallback回撥類是從Spring容器中獲取的，所以UserFeignFallback由spring建立。
UserFeign配置:
package com.example.feign;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import UserFeignFallback類：
package com.example.feign;
import org.springframework.stereotype.Component;
import java.util.List;
@Component
public class UserFeignFallback implements UserFeign {
@Override
public void save(User user) {
}
@Override
public User getUserByID(String id) {
User user = new User();
user.setId("100");
user.setName("fallback 回撥使用者");
return user;
}
@Override
public List<User> findAll() {
return null;
}
}為了模擬回撥失敗服務提供方，丟擲500錯誤。
@GetMapping("/{id}")
public User getUserByID(@PathVariable("id") String id) {
// return userMap.get(id);
throw new RuntimeException("服務端測試異常！");
}執行單元測試UserFeignTest.getUserByID控制檯輸出結果:
2018-08-18 11:47:59.800 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] ---> GET http://localhost:8080/user/1 HTTP/1.1
2018-08-18 11:47:59.800 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] ---> END HTTP (0-byte body)
2018-08-18 11:47:59.828 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] <--- HTTP/1.1 500 (27ms)
2018-08-18 11:47:59.828 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] connection: close
2018-08-18 11:47:59.828 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] content-type: application/json;charset=UTF-8
2018-08-18 11:47:59.828 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] date: Sat, 18 Aug 2018 03:47:59 GMT
2018-08-18 11:47:59.828 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] transfer-encoding: chunked
2018-08-18 11:47:59.828 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID]
2018-08-18 11:47:59.829 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] {"timestamp":1534564079825,"status":500,"error":"Internal Server Error","exception":"java.lang.RuntimeException","message":"服務端測試異常！","path":"/user/1"}
2018-08-18 11:47:59.829 INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign : [UserFeign#getUserByID] <--- END HTTP (167-byte body)
User{id='100', name='fallback 回撥使用者'}服務提供方丟擲的500錯誤程式碼，但是客戶端程式還可以正常執行輸出了UserFeignFallback.getUserByID方法返回的結果。
FallbackFactory工廠
上面的實現方式簡單，但是獲取不到HTTP請求錯誤狀態碼和資訊 ，這時就可以使用工廠模式來實現Fallback
同樣工廠實現類也要交由spring管理，同時結合UserFeignFallback使用，這裡需要注意的create方法返回值型別一定要實現Feign介面，否則會報錯。
UserFeignFactory只做了列印異常處理：
package com.example.feign;
import feign.hystrix.FallbackFactory;
import org.springframework.stereotype.Component;
@Component
public class UserFeignFactory implements FallbackFactory<UserFeign> {
private final UserFeignFallback userFeignFallback;
public UserFeignFactory(UserFeignFallback userFeignFallback) {
this.userFeignFallback = userFeignFallback;
}
@Override
public UserFeign create(Throwable cause) {
//列印下異常
cause.printStackTrace();
return userFeignFallback;
}
}UserFeign:
package com.example.feign;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import java.util.List;
@FeignClient(name = "user", url = "${user.url}",
/*fallback = UserFeignFallback.class*/
fallbackFactory = UserFeignFactory.class)
public interface UserFeign {
@PostMapping
void save(User user);
@GetMapping("/{id}")
User getUserByID(@PathVariable("id") String id);
@GetMapping
List<User> findAll();
}執行單元測試UserFeignTest.getUserByID可以看到控制檯列印的異常feign.FeignException更多資訊省略。
ErrorDecoder介面處理請求錯誤資訊，預設實現ErrorDecoder.Default丟擲FeignException異常
FeignException.status方法返回HTTP狀態碼，FallbackFactory.create預設情況下可以強制轉換成FeignException異常這樣就可以獲取到HTTP狀態碼了。
自定義ErrorDecoder
第一種:application.properties
全域性配置,通過application.properties配置檔案
feign.client.default-config=my-config
feign.client.config.my-config.error-decoder=com.example.feign.MyErrorDecoder錯誤解碼實現類MyErrorDecoder
package com.example.feign;
import feign.Response;
import feign.codec.ErrorDecoder;
public class MyErrorDecoder implements ErrorDecoder {
@Override
public Exception decode(String methodKey, Response response) {
return new MyFeignException(methodKey,response);
}
}自定義異常MyFeignException
package com.example.feign;
import feign.Response;
public class MyFeignException extends RuntimeException {
private final String methodKey;
private Response response;
MyFeignException(String methodKey, Response response) {
this.methodKey = methodKey;
this.response = response;
}
public Response getResponse() {
return response;
}
public String getMethodKey() {
return methodKey;
}
}第二種:@EnableFeignClients
全域性配置,@EnableFeignClients.defaultConfiguration註解
package com.example;
import com.example.feign.FeignClientsConfig;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
/**
* 啟動類
*
* @author: sunshaoping
* @date: Create by in 上午10:47 2018/8/7
*/
@EnableFeignClients(
defaultConfiguration = FeignClientsConfig.class
)
@SpringBootApplication
public class FeignApplication {
public static void main(String[] args) {
SpringApplication.run(FeignApplication.class, args);
}
}第三種:@FeignClient
作用範圍是Feign介面,優先順序要高於上面兩種，@FeignClient.configuration 註解
package com.example.feign;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import java.util.List;
@FeignClient(name = "user", url = "${user.url}",
/*fallback = UserFeignFallback.class*/
decode404 = true,
fallbackFactory = UserFeignFactory.class,
configuration = FeignClientsConfig.class
)
public interface UserFeign {
@PostMapping
void save(User user);
@GetMapping("/{id}")
User getUserByID(@PathVariable("id") String id);
@GetMapping
List<User> findAll();
}總結
本章節講了如下內容
Spring Cloud Feign HTTP請求異常Fallback容錯機制，它是基於Hystrix實現的，所以要通過配置引數feign.hystrix.enabled=true開啟該功能，及其兩種實現方式。
Fallback工廠方式引出了ErrorDecoder錯誤解碼自定義處理，有三種方式，可根據實際請求選擇，舉一反三其他自定義配置也可以通過這種方式實現如：Decoder、Encoder、Logger(第二、三章有介紹)。
如果開啟的
Hystrix就不要用feign的超時配置了,單位是毫秒feign.client.config.defalut.connect-timeout=10000
defalut是預設配置名稱，可以使用feign.client.default-config替換自定義名稱feign.client.default-config=my-config feign.client.config.my-config.connect-timeout=10000請使用如下屬性配置超時時間，單位毫秒
hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds=20000
樣例地址 spring-cloud-feign 分支 Spring-Cloud-Feign-之fallback
寫在最後
Spring Cloud Feign 系列持續更新中。。。。。歡迎關注
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