SpringCloud-4-Feign

Feign

1. Feign概述

feign是声明式的web service客户端，它让微服务之间的调用变得更简单了，类似controller调用service。Spring Cloud集成了Ribbon和Eureka，可在使用Feign时提供负载均衡的http客户端

Feign本质上是对Ribbon做了集成封装,相当于加了一层,更加符合开发者面向接口和注解的编程习惯,免去了RestTemplate的配置,这样同时不可避免的带来了性能的损失

2. 使用Feign做负载均衡

1. 创建Feign客户端

在API中提供Feign的接口

1. 导入依赖

<!--Feign-->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-feign</artifactId>
    <version>1.4.6.RELEASE</version>
</dependency>

2. 创建Feign接口

package com.wang.springcloud.service;

import com.wang.springcloud.pojo.Dept;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Service;
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;

//value为微服务的名称
@FeignClient(value = "SPRINGCLOUD-PROVIDER-DEPT")
@Service
public interface DeptClientService {

    @GetMapping("/dept/get/{id}")
    Dept queryById(@PathVariable("id") Long id);

    @GetMapping("/dept/list")
    List<Dept> queryAll();

    @PostMapping("/dept/add")
    Boolean addDept(Dept dept);

}

注意

• @FeignClient 声明该接口为Feign的客户端,value指定了用于负载均衡的服务名
• 接口中的方法的url对应provider中提供的url,本质上与Ribbon一样,只是这里省略了繁琐的RestTemplate配置,通过注解直接写在此处

2. 调用Feign

1. 导入依赖

我们首先依据SpringCloud-consumer-dept-8080创建了利用Feign做负载均衡的Module

同样的,依赖只需要将Ribbon替换为Feign

<!--Feign-->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-feign</artifactId>
    <version>1.4.6.RELEASE</version>
</dependency>

2. 在controller中调用Feign

package com.wang.springcloud.controller;

import com.wang.springcloud.pojo.Dept;
import com.wang.springcloud.service.DeptClientService;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiOperation;
import io.swagger.annotations.ApiParam;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@ApiModel("Consumer Controller")
@RestController
public class DeptConsumerController {

    @Autowired
    private DeptClientService service = null;

    @ApiOperation("通过部门编号查询一个部门")
    @RequestMapping(value = "/consumer/dept/get/{id}",method = RequestMethod.GET)
    public Dept get(@PathVariable("id") @ApiParam("部门编号") Long id) {
        return this.service.queryById(id);
    }

    @ApiOperation("通过部门名称添加一个部门")
    @RequestMapping(value = "/consumer/dept/add",method = RequestMethod.POST)
    public boolean add(@ApiParam("部门的名称") Dept dept){
        return this.service.addDept(dept);
    }

    @ApiOperation("查询全部的部门")
    @RequestMapping(value = "consumer/dept/list",method = RequestMethod.GET)
    public List<Dept> list() {
        return this.service.queryAll();
    }

}

注意

• 我们要使用Feign客户端,因此要将API定义的Feign客户端自动装配,引入controller中
• 调用的时候,我们只需要返回API接口中对应的方法即可

3. 在主启动类声明

package com.wang.springcloud;

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

//Ribbon 和 Eureka 整合以后,客户端可以直接调用,不用关心IP地址和端口号
@SpringBootApplication
@EnableEurekaClient
//开启Feign客户端支持
@EnableFeignClients
public class FeignDeptConsumer_8080 {
    public static void main(String[] args) {
        SpringApplication.run(FeignDeptConsumer_8080.class,args);
    }
}

3. 关于Feign负载均衡策略的一些思考

Feign由于封装了Ribbon,只是更加贴近JAVA的面向接口和注解编程的习惯,因此,自定义和更改负载均衡策略与Ribbon一致,依然是注册IRule接口

当自定义策略与SpringBoot主启动类不在同一级时,使用@RibbonClient注解中的configuration属性指定配置类

下面是在Feign配置负载均衡黑随机方式的配置类

package com.wang.springcloud.config;

import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.RandomRule;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;

@Configuration
public class ConfigBean {

    @Bean
    public IRule myRule() {
        return new RandomRule();
    }

}