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;
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。
- 依赖不同:一个是spring-cloud-starter-feign,一个是spring-cloud-starter-openfeign
- 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。
整体项目目录包括四个Module,分别为:eureka-server、feign-server-api、feign-server、feign-consumer。
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。
<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。
eureka-server整体代码结构目录如下:
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。
<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>
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
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。
启动成功后,控制台输出如下:
进入到eureka-server 的dashboard,可以看到eureka-server已经上线:
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。
<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>
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 + "]";
}
}
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);
}
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。
<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>
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
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);
}
}
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);
}
}
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
。
1> 修改FeignServerApplication
的配置:
2> 复制出一个FeignServerApplication配置:
3> 修改第二启动类配置名为:FeignServerApplication-8082
,启动端口为8082
:
4> 运行FeignServerApplication-8082
:
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
:
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。
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>
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。
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。
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
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。
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
。
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
然后我们去看feign-server-8081、feign-server-8082的控制台输出:
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)?