【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例

一、Feign概述

Feign是一个声明式的客户端负载均衡器;采用的是基于接口的注解;整合了ribbon,具有负载均衡的能力;整合了Hystrix,具有熔断的能力;

1、为什么会使用Feign代替Ribbon

使用RestTemplate + ribbon的方式来进行服务间的调用,会导致我们每次去调用其他服务的一个接口,都要单独写一些代码。

而Feign是声明式调用,可以让我们不用写代码,直接用一些接口和注解就可以完成对其他服务的调用。

2、Feign和OpenFeign的区别?

  1. 依赖不同:一个是spring-cloud-starter-feign,一个是spring-cloud-starter-openfeign
  2. 支持的注解:OpenFeign是springcloud在Feign的基础上支持了SpringMVC的注解,如@RequestMapping等等。
    即:OpenFeign的@FeignClient可以解析SpringMVC的@RequestMapping注解下的接口,并通过动态代理的方式产生实现类,实现类中做负载均衡并调用其他服务。

二、Feign实现负载均衡

整体项目目录包括四个Module,分别为:eureka-server、feign-server-api、feign-server、feign-consumer。
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第1张图片

其中eureka-server作为服务注册中心、feign-server-api作为服务提供者给consumer引入、feign-server作为具体的服务提供者实现、feign-consumer作为服务消费者。

0、最上层父项目spring-cloud-center的pom.xml文件


<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.3.7.RELEASEversion>
        <relativePath/> 
    parent>
    <modelVersion>4.0.0modelVersion>
    <packaging>pompackaging>

    
    <modules>
        <module>feign-server-apimodule>
        <module>feign-servermodule>
        <module>feign-consumermodule>
        <module>eureka-servermodule>
    modules>

    <artifactId>spring-cloud-centerartifactId>
    <groupId>com.saintgroupId>
    <version>0.0.1-SNAPSHOTversion>
    <name>spring-cloud-centername>

    <properties>
        <java.version>1.8java.version>
    properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-dependenciesartifactId>
                <version>2.3.7.RELEASEversion>
                <type>pomtype>
                <scope>importscope>
            dependency>
            
            <dependency>
                <groupId>org.springframework.cloudgroupId>
                <artifactId>spring-cloud-dependenciesartifactId>
                <version>Hoxton.SR8version>
                <type>pomtype>
                <scope>importscope>
            dependency>
            
            <dependency>
                <groupId>com.alibaba.cloudgroupId>
                <artifactId>spring-cloud-alibaba-dependenciesartifactId>
                <version>2.2.5.RELEASEversion>
                <type>pomtype>
                <scope>importscope>
            dependency>
        dependencies>
    dependencyManagement>

    <build>
        <plugins>
            
            <plugin>
                <groupId>org.apache.maven.pluginsgroupId>
                <artifactId>maven-compiler-pluginartifactId>
                <configuration>
                    <source>1.8source>
                    <target>1.8target>
                    <encoding>UTF-8encoding>
                configuration>
            plugin>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
            plugin>
        plugins>
    build>

project>

关于Spring-cloud和SpringBoot的版本对应关系,参考博文:SpringBoot、SpringCloud、SpringCloudAlibaba的版本对应关系。

1、搭建服务注册中心eureka-server

eureka-server整体代码结构目录如下:
在这里插入图片描述
其整体很简单、仅仅包含一个pom.xml文件、一个配置文件、一个启动类。

1、pom.xml


<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>spring-cloud-centerartifactId>
        <groupId>com.saintgroupId>
        <version>0.0.1-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>

    <artifactId>eureka-serverartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <description>eureka-serverdescription>

    <dependencies>

        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-netflix-eureka-serverartifactId>
        dependency>

        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>

        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starterartifactId>
            <optional>trueoptional>
        dependency>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-autoconfigureartifactId>
        dependency>
    dependencies>

project>

2、修改配置文件application.yml

server:
  port: 10010
spring:
  application:
    name: eureka-server
eureka:
  client:
    # 把自身注册到Eureka-server中
    register-with-eureka: true
    # 服务注册中心不需要去检索其他服务
    fetch-registry: false
    # 指定服务注册中心的位置
    service-url:
      defaultZone: http://localhost:10010/eureka
  instance:
    hostname: localhost

3、修改启动类

package com.saint;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

/**
 * @author Saint
 */
@EnableEurekaServer
@SpringBootApplication
public class EurekaServerApplication {

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

这里和普通的启动有一个区别:需要加上 @EnableEurekaServer 注解开启Eureka-Server。

4、启动eureka-server

启动成功后,控制台输出如下:
在这里插入图片描述
进入到eureka-server 的dashboard,可以看到eureka-server已经上线:
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第2张图片

2、搭建服务提供者API(feign-server-api)

feign-server-api整体代码结构目录如下:
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第3张图片

其中包含一个pom.xml文件、一个用户类User、一个标注@RequestMapping注解的接口ServiceA。

1、pom.xml


<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>spring-cloud-centerartifactId>
        <groupId>com.saintgroupId>
        <version>0.0.1-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>
    <artifactId>feign-server-apiartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <description>feign test service provider apidescription>

    <dependencies>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
    dependencies>

project>

2、User

package com.saint.feign.model;

/**
 * @author Saint
 */
public class User {
    private Long id;
    private String name;
    private Integer age;

    public User() {
    }

    public User(Long id, String name, Integer age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
}

3、ServiceA

package com.saint.feign.service;

import com.saint.feign.model.User;
import org.springframework.web.bind.annotation.*;

/**
 * @author Saint
 */
@RequestMapping("/user")
public interface ServiceA {
    @RequestMapping(value = "/sayHello/{id}", method = RequestMethod.GET)
    String sayHello(@PathVariable("id") Long id,
                    @RequestParam("name") String name,
                    @RequestParam("age") Integer age);

    @RequestMapping(value = "/", method = RequestMethod.POST)
    String createUser(@RequestBody User user);

    @RequestMapping(value = "/{id}", method = RequestMethod.PUT)
    String updateUser(@PathVariable("id") Long id, @RequestBody User user);

    @RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
    String deleteUser(@PathVariable("id") Long id);

    @RequestMapping(value = "/{id}", method = RequestMethod.GET)
    User getById(@PathVariable("id") Long id);
}

3、搭建服务提供者implement(feign-server)

feign-server-api整体代码结构目录如下:
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第4张图片

其中包含一个pom.xml文件、一个application配置文件、一个启动类、一个Controller。

1、pom.xml


<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>spring-cloud-centerartifactId>
        <groupId>com.saintgroupId>
        <version>0.0.1-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>

    <artifactId>feign-serverartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <description>feign test service providerdescription>

    <dependencies>

        <dependency>
            <groupId>com.saintgroupId>
            <artifactId>feign-server-apiartifactId>
            <version>0.0.1-SNAPSHOTversion>
        dependency>

        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-netflix-eureka-clientartifactId>
        dependency>

        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
    dependencies>

project>

2、application.yml

server:
  port: 8081
spring:
  application:
    name: service-a
eureka:
  client:
    # 将当前服务注册到服务注册中心
    service-url:
      defaultZone: http://localhost:10010/eureka

3、启动类FeignServerApplication

package com.saint.feign;

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

/**
 * @author Saint
 */
@EnableEurekaClient
@SpringBootApplication
public class FeignServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(FeignServerApplication.class, args);
    }
}

4、编写ServiceAController

ServiceAController实现feign-server-api模块下的ServiceA,提供具体的业务实现。

package com.saint.feign.controller;

import com.saint.feign.model.User;
import com.saint.feign.service.ServiceA;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author Saint
 */
@RestController
public class ServiceAController implements ServiceA {
    @Override
    public String sayHello(@PathVariable("id") Long id,
                           @RequestParam("name") String name,
                           @RequestParam("age") Integer age) {
        System.out.println("打招呼,id=" + id + ", name=" + name + ", age=" + age);
        return "{'msg': 'hello, " + name + "'}";
    }

    @Override
    public String createUser(@RequestBody User user) {
        System.out.println("创建用户," + user);
        return "{'msg': 'success'}";
    }

    @Override
    public String updateUser(@PathVariable("id") Long id, @RequestBody User user) {
        System.out.println("更新用户," + user);
        return "{'msg': 'success'}";
    }

    @Override
    public String deleteUser(@PathVariable("id") Long id) {
        System.out.println("删除用户,id=" + id);
        return "{'msg': 'success'}";
    }

    @Override
    public User getById(@PathVariable("id") Long id) {
        System.out.println("查询用户,id=" + id);
        return new User(1L, "张三", 20);
    }
}

5、启动service-a服务实例1(8081端口)

服务启动成功后,控制台输出如下:
在这里插入图片描述

再看eureka-server dashboard中多了一个 SERVICE-A 服务,并且其有一个实例 192.168.1.6:service-a:8081
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第5张图片

6、启动service-a服务实例2(8082端口)

1> 修改FeignServerApplication的配置:
在这里插入图片描述

2> 复制出一个FeignServerApplication配置:
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第6张图片

3> 修改第二启动类配置名为:FeignServerApplication-8082,启动端口为8082
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第7张图片

4> 运行FeignServerApplication-8082
在这里插入图片描述

5> 启动之后,看eureka-server dashboard中SERVICE-A 服务多了一个实例 192.168.1.6:service-a:8082
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第8张图片

4、搭建服务消费者feign-consumer

feign-consumer整体代码结构目录如下:
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第9张图片

其包含一个pom.xml文件、一个application配置文件、一个启动类、一个FeignClient接口、一个Controller。

1、pom.xml

这里使用的是open-feign,想使用老版本的feign把代码中的注释放开;并把spring-cloud-starter-openfeign依赖注掉即可。


<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>spring-cloud-centerartifactId>
        <groupId>com.saintgroupId>
        <version>0.0.1-SNAPSHOTversion>
    parent>
    <modelVersion>4.0.0modelVersion>

    <artifactId>feign-consumerartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <description>feign test consumerdescription>

    <dependencies>

        <dependency>
            <groupId>com.saintgroupId>
            <artifactId>feign-server-apiartifactId>
            <version>0.0.1-SNAPSHOTversion>
        dependency>

        






        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-openfeignartifactId>
        dependency>

        
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-netflix-eureka-clientartifactId>
        dependency>

        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
    dependencies>

project>

2、修改配置文件application.yml

server:
  port: 9090
spring:
  application:
    name: service-b
eureka:
  client:
    # 将当前服务注册到服务注册中心
    service-url:
      defaultZone: http://localhost:10010/eureka

注:服务端口为9090,后面我们进行接口调用的时候会用到。

3、修改启动类

package com.saint.feign;

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

/**
 * @author Saint
 */
@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class FeignConsumerApplication {
    public static void main(String[] args) {
        SpringApplication.run(FeignConsumerApplication.class, args);
    }
}

其中的@EnableFeignClients注解负责使@FeignClient注解生效,可以被扫描到。

4、FeignClient接口(ServiceAClient)

package com.saint.feign.client;
import com.saint.feign.service.ServiceA;
import org.springframework.cloud.openfeign.FeignClient;

/**
 * @author Saint
 */
@FeignClient("SERVICE-A")
public interface ServiceAClient extends ServiceA {
}

FeignClient接口要实现feign-server-api中的ServiceA接口,以表明当前FeignClient针对的对象

5、编写ServiceBController

package com.saint.feign.controller;

import com.saint.feign.model.User;
import com.saint.feign.client.ServiceAClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;


@RestController
@RequestMapping("/ServiceB/user")  
public class ServiceBController {
	
	@Autowired
	private ServiceAClient serviceA;
	
	@RequestMapping(value = "/sayHello/{id}", method = RequestMethod.GET)
	public String greeting(@PathVariable("id") Long id, 
			@RequestParam("name") String name, 
			@RequestParam("age") Integer age) {
		return serviceA.sayHello(id, name, age);
	}
	
	@RequestMapping(value = "/", method = RequestMethod.POST)
	public String createUser(@RequestBody User user) {
		return serviceA.createUser(user);
	}

	@RequestMapping(value = "/{id}", method = RequestMethod.PUT)
	public String updateUser(@PathVariable("id") Long id, @RequestBody User user) {
		return serviceA.updateUser(id, user); 
	}

	@RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
	public String deleteUser(@PathVariable("id") Long id) {
		return serviceA.deleteUser(id);
	}

	@RequestMapping(value = "/{id}", method = RequestMethod.GET)
	public User getById(@PathVariable("id") Long id) {
		return serviceA.getById(id);
	}
	
}

ServiceBController中通过FeignClient做负载均衡调用SERVICE-A服务中提供的接口。

6、启动feign-consumer

启动成功后,看eureka-server dashboard中多了一个 SERVICE-B 服务,并且其有一个实例 192.168.1.6:service-b:9090
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第10张图片

4、使用浏览器进行调用服务消费者

上述步骤中,我们已经依次启动了eureka-server、feign-server-8081、feign-server-8082、feign-consumer;三个服务、四个实例。

此处我们针对服务消费者ribbon-feign-sample-consumer做四次接口调用,均为:http://localhost:9090/ServiceB/user/sayHello/1?name=saint&age=18

【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第11张图片

然后我们去看feign-server-8081、feign-server-8082的控制台输出:

1> feign-server-8081控制台输出:
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第12张图片

2> feign-server-8082控制台输出:
【云原生&微服务九】SpringCloud之Feign实现声明式客户端负载均衡详细案例_第13张图片

3> 结果说明:
我们可以发现,四个请求,ribbon-feign-sample-8081和ribbon-feign-sample-8082各分担了两个请求。

从现象上来看,已经Feign实现了负载均衡,并且默认是按照轮询的方式。

下文我们接着讨论 Feign是如何实现负载均衡(源码分析)?

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