Feign

集成工具

• 遠程呼叫：宣告式客戶端
• ribbon 負載均衡和重試
• hystrix 降級和熔斷

feign 宣告式客戶端介面

微服務應用中，ribbon 和 hystrix 總是同時出現，feign 整合了兩者，并提供了宣告式消費者客戶端

• 用 feign 代替 hystrix+ribbon
  
  只需要宣告一個抽象介面，就可以通過介面做遠程呼叫，不需要再使用 RestTemplate 來呼叫

// 呼叫遠程的商品服務，獲取訂單的商品串列
// 通過注解，配置：
// 1. 呼叫哪個服務
// 2. 呼叫服務的哪個路徑
// 3. 向路徑提交什么引數資料
@FeignClient(name="item-service")//item-service指在eureka中注冊的服務名
public interface ItemClient {
    @GetMapping("/{orderId}")
    JsonResult<List<Item>> getItems(@PathVariable String orderId);//@PathVariable在這里是指向介面傳遞的引數
}

在這里使用 @GetMapping("/{orderId}")， 指定的是向遠程服務呼叫的路徑

Demo

1.新建springboot模塊，添加依賴

2.application.yml配置

# 應用名稱
spring:
  application:
    name: feign

# Actuator Web 訪問埠
server:
  port: 3001
eureka:
  client:
    service-url:
      defaultZone: http://eureka1:2001/eureka,http://eureka2:2002/eureka

1）測驗遠程呼叫（宣告式客戶端介面）
1.啟動類添加Feign注解

@EnableFeignClients

2.新建Feign包，創建ItemFeignService介面

import cn.tedu.sp01.pojo.Item;
import cn.tedu.sp01.util.JsonResult;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;

import java.util.List;

//根據服務id，從注冊表得到主機地址
@FeignClient(name = "item-service")
public interface ItemFeignService {
    @GetMapping("/{orderId}")
    JsonResult<List<Item>> getItems(@PathVariable(value = "orderId") String orderId);

    @PostMapping("/decreaseNumber")
    JsonResult<?> decreaseNumber(@RequestBody List<Item> items);

}

創建UserFeignService介面

import cn.tedu.sp01.pojo.User;
import cn.tedu.sp01.util.JsonResult;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient(name= "user-service")
public interface UserFeignService {
    @GetMapping("/{userId}")
    JsonResult<User> getUser(@PathVariable(value = "userId") Integer userId);


    @GetMapping(value = "/{userId}/score")
    JsonResult<?> addScore(@PathVariable(value = "userId") Integer userId,
                           @RequestParam(value = "score") Integer score);//@RequestParam在Controller中可以省略，此處不能省略
}

創建OrderFeignService介面

import cn.tedu.sp01.pojo.Order;
import cn.tedu.sp01.util.JsonResult;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

@FeignClient("order-service")
public interface OrderFeignService {
    @GetMapping("/{orderId}")
    JsonResult<Order> getOrder(@PathVariable(value = "orderId") String orderId);

    @GetMapping("/")
    JsonResult<?> addOrder();
}

3.創建controller

import cn.tedu.sp01.pojo.Item;
import cn.tedu.sp01.pojo.Order;
import cn.tedu.sp01.pojo.User;
import cn.tedu.sp01.util.JsonResult;
import cn.tedu.sp09.feign.ItemFeignService;
import cn.tedu.sp09.feign.OrderFeignService;
import cn.tedu.sp09.feign.UserFeignService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@Slf4j
public class ItemController {
    @Autowired
    private ItemFeignService itemFeignService;

    @Autowired
    private UserFeignService userFeignService;

    @Autowired
    private OrderFeignService orderFeignService;

    @GetMapping("/item-service/{orderId}")
    public JsonResult<List<Item>> getItems(@PathVariable String orderId){
        return itemFeignService.getItems(orderId);
    }
    @PostMapping("/item-service/descrease")
    public JsonResult<?> decreaseNumber(@RequestBody List<Item> items){
        return itemFeignService.decreaseNumber(items);
    }
    @GetMapping("/user-service/{userId}")
    public JsonResult<User> getUser(@PathVariable Integer userId){
        return userFeignService.getUser(userId);
    }
    @GetMapping("/user-service/{userId}/score")
    public JsonResult<?> addScore(@PathVariable Integer userId,
                                  Integer score){
        return userFeignService.addScore(userId, score);
    }
    @GetMapping("/order-service/{orderId}")
    public JsonResult<Order> getOrder(@PathVariable String orderId){
        return orderFeignService.getOrder(orderId);
    }
    @GetMapping("/order-service/")
    public JsonResult<?> addOrder(){
        return orderFeignService.addOrder();
    }
}

測驗：

遠程呼叫成功！！！

呼叫流程：

feign + ribbon 負載均衡和重試

無需額外配置，feign 默認已啟用了 ribbon 負載均衡和重試機制，可以通過配置對引數進行調整
重試的默認配置引數:

ConnectTimeout=1000
ReadTimeout=1000
MaxAutoRetries=0
MaxAutoRetriesNextServer=1