【Spring Cloud 基础设施搭建系列】Spring Cloud Demo项目使用Feign实现声明式REST调用

文章目录

Feign简介
微服务整合Feign
参考
源代码

Feign简介

Feign是Netflix开发的声明式、模板化的HTTP客户端，其灵感来自Retrofit、JAXRS-2.0以及WebSocket。Feign可帮助我们更加便捷、优雅地调用HTTPAPI。

在Spring Cloud中，使用Feign非常简单—创建一个接口，并在接口上添加一些注解，代码就完成了。Feign支持多种注解，例如Feign自带的注解或者JAX-RS注解等。
Spring Cloud对Feign进行了增强，使Feign支持了Spring MVC注解，并整合了Ribbon和Eureka，从而让Feign的使用更加方便。

微服务整合Feign

往cloud-service-member,cloud-service-order的pom文件中都加入Feign的依赖。

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

<artifactId>spring-cloud-starter-feign</artifactId>已经过期，推荐使用<artifactId>spring-cloud-starter-openfeign</artifactId>

创建一个Feign接口，并添加@FeignClient注解。

cloud-service-member

package com.cc.cloud.member.feign;

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

import java.util.List;

@FeignClient("cloud-service-order")
public interface OrderFeign {

    @RequestMapping("/order/orders")
    List<String> getAllOrderList();
}

修改Controller代码，让其调用Feign接口。

package com.cc.cloud.member.controller;

import com.cc.cloud.member.feign.OrderFeign;
import com.google.common.collect.Lists;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping("/member")
public class MemberController {

    private OrderFeign orderFeign;


    @Autowired
    public void setOrderFeign(OrderFeign orderFeign) {
        this.orderFeign = orderFeign;
    }

    @RequestMapping("/orders")
    @ResponseStatus(HttpStatus.OK)
    public List<String> getOrderList() {
        return orderFeign.getAllOrderList();
    }

    @RequestMapping("/members")
    @ResponseStatus(HttpStatus.OK)
    public List<String> getMemberList() {
        List<String> memberList = Lists.newArrayList();
        memberList.add("member 1");
        memberList.add("member 2");
        memberList.add("member 3");
        return memberList;
    }

}

cloud-service-order

package com.cc.cloud.order.feign;

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

import java.util.List;

@FeignClient("cloud-service-member")
public interface MemberFeign {
    @RequestMapping("/member/members")
    List<String> getAllMemberList();
}

修改Controller代码，让其调用Feign接口。

package com.cc.cloud.order.controller;

import com.cc.cloud.order.feign.MemberFeign;
import com.google.common.collect.Lists;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;
@RestController
@RequestMapping("/order")
public class OrderController {

    private MemberFeign memberFeign;

    @Autowired
    public void setMemberFeign(MemberFeign memberFeign) {
        this.memberFeign = memberFeign;
    }

    @RequestMapping("/members")
    @ResponseStatus(HttpStatus.OK)
    public List<String> getMemberList() {
        return memberFeign.getAllMemberList();
    }


    @GetMapping("/orders")
    @ResponseStatus(HttpStatus.OK)
    public List<String> getOrders() {
        List<String> orders = Lists.newArrayList();
        orders.add("order 1");
        orders.add("order 2");
        return orders;
    }
}

@FeignClient 注解中的cloud-service-member是一个任意的客户端名称，用于创建Ribbon负载均衡器。在本例中，由于使用了Eureka，所以Ribbon会把cloud-service-member解析成Eureka Server服务注册表中的服务。当然，如果不想使用Eureka，可使用service.ribbon.listofServers属性配置服务器列表.
还可使用url属性指定请求的URL（URL可以是完整的URL或者主机名），例如
@FeignClient（name =“cloud-service-member”，url=“http://localhost:8762”）。

修改启动类，为其添加@EnableFeignClients注解，如下：

package com.cc.cloud.member;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class MemberApp {
    public static void main(String[] args) {
        SpringApplication.run(MemberApp.class, args);
    }
}

package com.cc.cloud.order;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class OrderApp {
    public static void main(String[] args) {
        SpringApplication.run(OrderApp.class, args);
    }
}