Feign 简介

Feign 是声明式的服务调用工具，我们只需创建一个接口并用注解的方式来配置它，就可以实现对某个服务接口的调用，简化了直接使用 RestTemplate 来调用服务接口的开发量。
接下来，我们将新建product-service和order-service，实现product-service以HTTP Rest方式调用order-service的服务。

1.新建Spring boot Web项目，application name 为 product-service

在pom.xml中引入依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

spring-cloud-starter-alibaba-nacos-discovery作用为向Nacos server注册服务。
spring-cloud-starter-openfeign作用为实现服务调用。

2.修改application.yml配置文件

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
  application:
    name: product-service
server:
  port: 8083

3.在启动类上添加@EnableDiscoveryClient、@EnableFeignClients注解

package com.example.productservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
public class ProductServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(ProductServiceApplication.class, args);
    }

}

4.编写OrderClient Interface

注：/api/v1/order/test 会在下面order-service声明。
OrderClient.java

package com.example.productservice.client;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Component
@FeignClient("order-service")
public interface OrderClient {
    @RequestMapping(method = RequestMethod.GET, value = "/api/v1/order/test")
    String callOrder();
}

5.编写Controller和service

ProductController.java

package com.example.productservice.controller;

import com.example.productservice.service.ProductService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ProductController {
    @Autowired
    ProductService productService;

    @RequestMapping(value = "testCallOrder", method = RequestMethod.GET)
    public String testCallOrder() {
        return productService.callOrder();
    }
}

ProductService.java

package com.example.productservice.service;

import com.example.productservice.client.OrderClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class ProductService {

    @Autowired
    OrderClient orderClient;

    public String callOrder() {
        String response = orderClient.callOrder();
        return response;
    }
}

6.新建Spring boot Web项目，application name 为 order-service

同样在pom.xml中引入依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

7.修改application.yml配置文件

spring:
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
  application:
    name: -service
server:
  port: 8082

8.在启动类上添加@EnableDiscoveryClient注解

package com.example.orderservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@SpringBootApplication
@EnableDiscoveryClient
public class OrderServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(OrderServiceApplication.class, args);
    }

}

9.新建Controller

package com.example.orderservice.controller;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/api/v1/order")
public class OrderController {
    @RequestMapping("/test")
    public Object test(){
        return "Hello,this is order-service";
    }
}

测试

启动product-service和order-service
访问 http://localhost:8083/testCallOrder

openFeign.png

至此，利用openFeign进行服务间调用完成。

服务间调用-openFeign