【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

文章目录

  • 一、Feign概述
    • 1、为什么会使用Feign代替Ribbon
    • 2、Feign和OpenFeign的区别?
  • 二、Feign实现负载均衡
    • 0、最上层父项目spring-cloud-center的pom.xml文件
    • 1、搭建服务注册中心eureka-server
      • 1、pom.xml
      • 2、修改配置文件application.yml
      • 3、修改启动类
      • 4、启动eureka-server
    • 2、搭建服务提供者API(feign-server-api)
      • 1、pom.xml
      • 2、User
      • 3、ServiceA
    • 3、搭建服务提供者implement(feign-server)
      • 1、pom.xml
      • 2、application.yml
      • 3、启动类FeignServerApplication
      • 4、编写ServiceAController
      • 5、启动service-a服务实例1(8081端口)
      • 6、启动service-a服务实例2(8082端口)
    • 4、搭建服务消费者feign-consumer
      • 1、pom.xml
      • 2、修改配置文件application.yml
      • 3、修改启动类
      • 4、FeignClient接口(ServiceAClient)
      • 5、编写ServiceBController
      • 6、启动feign-consumer
    • 5、使用浏览器进行调用服务消费者

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

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

<?xml version="1.0" encoding="UTF-8"?>
<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.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.7.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <packaging>pom</packaging>

    <!--子模块-->
    <modules>
        <module>feign-server-api</module>
        <module>feign-server</module>
        <module>feign-consumer</module>
        <module>eureka-server</module>
    </modules>

    <artifactId>spring-cloud-center</artifactId>
    <groupId>com.saint</groupId>
    <version>0.0.1-SNAPSHOT</version>
    <name>spring-cloud-center</name>

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

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.3.7.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <!--整合spring cloud-->
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Hoxton.SR8</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <!--整合spring cloud alibaba-->
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>2.2.5.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <!-- java编译插件 -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </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:
【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
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

<?xml version="1.0" encoding="UTF-8"?>
<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-center</artifactId>
        <groupId>com.saint</groupId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>eureka-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <description>eureka-server</description>

    <dependencies>

        <!--集成Eureka-server-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </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:
【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
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

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

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

<?xml version="1.0" encoding="UTF-8"?>
<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-center</artifactId>
        <groupId>com.saint</groupId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>feign-server-api</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <description>feign test service provider api</description>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </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

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

<?xml version="1.0" encoding="UTF-8"?>
<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-center</artifactId>
        <groupId>com.saint</groupId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>feign-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <description>feign test service provider</description>

    <dependencies>

        <dependency>
            <groupId>com.saint</groupId>
            <artifactId>feign-server-api</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

        <!--集成eureka-client-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </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:
【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

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

6、启动service-a服务实例2(8082端口)

1> 修改FeignServerApplication的配置:
【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

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

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

4> 运行FeignServerApplication-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

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

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

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。

<?xml version="1.0" encoding="UTF-8"?>
<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-center</artifactId>
        <groupId>com.saint</groupId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>feign-consumer</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <description>feign test consumer</description>

    <dependencies>

        <dependency>
            <groupId>com.saint</groupId>
            <artifactId>feign-server-api</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

        <!--集成feign PS: 博主使用的SpringCloud版本内部没有管理feign的版本,而是管理的open-feign版本-->
<!--        <dependency>-->
<!--            <groupId>org.springframework.cloud</groupId>-->
<!--            <artifactId>spring-cloud-starter-feign</artifactId>-->
<!--            <version>1.4.7.RELEASE</version>-->
<!--        </dependency>-->

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

        <!--集成eureka-client-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </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

5、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

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

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

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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