微服务之间的调用（Ribbon与Feign）

概述

在前面的文章中，我们讲了使用Eureka作为服务注册中心，在服务启动后，各个微服务会将自己注册到Eureka server。那么服务之间是如何调用？又是如何进行负载均衡的呢？本文讲讲服务之间调用及负载均衡Ribbon。

目前，在Spring cloud 中服务之间通过restful方式调用有两种方式
- restTemplate+Ribbon
- feign

从实践上看，采用feign的方式更优雅（feign内部也使用了ribbon做负载均衡）。

本文使用如下的项目实例来分别演示这两种写法。
- hello服务，读取数据库，返回信息
- world服务，返回信息
- helloworld服务，调用了hello服务和world服务（restTemplate+Ribbon方式）
- helloworldfeign服务，调用了hello服务和world服务（feign方式）

本文项目代码：springcloud-demo
如何理解客户端Ribbon
zuul也有负载均衡的功能，它是针对外部请求做负载，那客户端ribbon的负载均衡又是怎么一回事？

客户端ribbon的负载均衡，解决的是服务发起方（在Eureka注册的服务）对被调用的服务的负载，比如我们查询商品服务要调用显示库存和商品明细服务，通过商品服务的接口将两个服务组合，可以减少外部应用的请求，比如手机App发起一次请求即可，可以节省网络带宽，也更省电。

ribbon是对服务之间调用做负载，是服务之间的负载均衡，zuul是可以对外部请求做负载均衡。

hello服务与world服务

hello服务
Git项目代码：hello
pom.xml

<dependencies>        <dependency>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter</artifactId>        </dependency>        <dependency>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter-test</artifactId>            <scope>test</scope>        </dependency>        <dependency>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter-web</artifactId>        </dependency>        <dependency>            <groupId>org.springframework.cloud</groupId>            <artifactId>spring-cloud-starter-eureka</artifactId>        </dependency>                <!--connect the db-->        <dependency>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter-data-jpa</artifactId>            <version>1.5.4.RELEASE</version>        </dependency>        <dependency>            <groupId>mysql</groupId>            <artifactId>mysql-connector-java</artifactId>            <version>5.1.31</version>            <scope>runtime</scope>        </dependency>        <dependency>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-starter-actuator</artifactId>            <version>1.5.6.RELEASE</version>        </dependency>    </dependencies>    <dependencyManagement>        <dependencies>            <dependency>                <groupId>org.springframework.cloud</groupId>                <artifactId>spring-cloud-dependencies</artifactId>                <version>Dalston.SR2</version>                <type>pom</type>                <scope>import</scope>            </dependency>        </dependencies>    </dependencyManagement>

启动类HelloApplication：

package com.example.hello;import com.example.hello.model.Info;import com.example.hello.repository.InfoRepository;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.boot.CommandLineRunner;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import org.springframework.context.annotation.Bean;@EnableDiscoveryClient@SpringBootApplicationpublic class HelloApplication {    private static final Logger log= LoggerFactory.getLogger(HelloApplication.class);    public static final String KEY="Database";    public static final String VALUE="MYSQL FROM BILLJIANG";    public static void main(String[] args) {        SpringApplication.run(HelloApplication.class, args);    }    @Bean    public CommandLineRunner initDatabase(InfoRepository repository){        return (args) -> {            repository.save(new Info(KEY,VALUE));        };    }}

入口类HelloController：

package com.example.hello.controller;import com.example.hello.HelloApplication;import com.example.hello.model.HelloMessage;import com.example.hello.model.Info;import com.example.hello.repository.InfoRepository;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.cloud.client.ServiceInstance;import org.springframework.cloud.client.discovery.DiscoveryClient;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RestController;import java.util.List;@RestControllerpublic class HelloController {    @Autowired    private DiscoveryClient discoveryClient;    @Autowired    private InfoRepository infoRepository;    @GetMapping("/")    public String home(){        return "hello";    }    @GetMapping("/message")    public HelloMessage getMessage() {        HelloMessage helloMessage = new HelloMessage();        helloMessage.setName(getLocalInstanceInfo());        helloMessage.setMessage(getInfoFromDatabase());        return helloMessage;    }    private String getLocalInstanceInfo() {        ServiceInstance serviceInstance = discoveryClient.getLocalServiceInstance();        return serviceInstance.getServiceId() + ":" + serviceInstance.getHost() + ":" + serviceInstance.getPort();    }    private String getInfoFromDatabase() {        List<Info> infoList = infoRepository.findByName(HelloApplication.KEY);        for (Info info : infoList) {            return info.toString();        }        return "(no database info)";    }}

配置文件application.yml:

#随机端口server:  port: 0#服务注册中心eureka:  client:    service-url:      default-zone: http://localhost:8761/eureka  instance:    instance-id: ${spring.application.name}:${spring.application.instance_id:${random.value}}#数据源spring:  application:    name: hello  datasource:    url: jdbc:mysql://127.0.0.1:3306/${{MYSQL_DATABASE}:foodb}    username: ${{MYSQL_USERNAME}:root}    password: ${{MYSQL_PASSWORD}:billjiang}    testWhileIdle: true    validationQuery: SELECT 1  jpa:    show-sql: true    hibernate:      ddl-auto: update      naming-strategy: org.hibernate.cfg.ImprovedNamingStrategy      properties:        hibernate:        dialect: org.hibernate.dialect.MySQL5Dialect  zipkin:    base-url: http://127.0.0.1:9411

其他类略，请参照源码：

world
world服务与hello服务类似，不过没有连接数据库
项目代码：world

helloworld调用hello服务和world服务

采用restTemplate+Ribbon调用服务。
项目代码：helloworld

启动类HelloworldApplication：
配置restTemplate的Bean

package com.example.helloworld;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import org.springframework.cloud.client.loadbalancer.LoadBalanced;import org.springframework.context.annotation.Bean;import org.springframework.web.client.RestTemplate;@SpringBootApplication@EnableDiscoveryClientpublic class HelloworldApplication {    public static void main(String[] args) {        SpringApplication.run(HelloworldApplication.class, args);    }    @Bean    @LoadBalanced    RestTemplate restTemplate() {        return new RestTemplate();    }}

入口类HelloworldController：

package com.example.helloworld.controller;import com.example.helloworld.model.HelloMessage;import com.example.helloworld.model.HelloworldMessage;import com.example.helloworld.model.WorldMessage;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.cloud.client.loadbalancer.LoadBalanced;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RestController;import org.springframework.web.client.RestTemplate;/** * @author billjiang [e-mail] * @create 17-8-22 */@RestControllerpublic class HelloworldController {    private static final Logger log = LoggerFactory.getLogger(HelloworldController.class);    private static final String HELLO_SERVICE_NAME = "hello";    private static final String WORLD_SERVICE_NAME = "world";    @Autowired    private RestTemplate restTemplate;    @GetMapping("/")    public String home() {        return "hello world";    }    @GetMapping("/message")    public HelloworldMessage getMessage() {        HelloMessage hello = getMessageFromHelloService();        WorldMessage world = getMessageFromWorldService();        HelloworldMessage helloworld = new HelloworldMessage();        helloworld.setHello(hello);        helloworld.setWord(world);        log.debug("Result helloworld message:{}", helloworld);        return helloworld;    }    private HelloMessage getMessageFromHelloService() {        HelloMessage hello = restTemplate.getForObject("http://hello/message", HelloMessage.class);        log.debug("From hello service : {}.", hello);        return hello;    }    private WorldMessage getMessageFromWorldService() {        WorldMessage world = restTemplate.getForObject("http://world/message", WorldMessage.class);        log.debug("From world service : {}.", world);        return world;    }}

测试：

helloworldfeign调用hello服务和world服务

feign方式调用服务，项目代码参考：helloworldfeign
pom.xml引入feignx

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

配置启动类注解：

package com.example.helloworldfeign;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import org.springframework.cloud.netflix.feign.EnableFeignClients;@SpringBootApplication@EnableDiscoveryClient@EnableFeignClientspublic class HelloworldFeignApplication {    public static void main(String[] args) {        SpringApplication.run(HelloworldFeignApplication.class, args);    }}

被调用接口HelloService

package com.example.helloworldfeign.service;import com.example.helloworldfeign.model.HelloMessage;import org.springframework.cloud.netflix.feign.FeignClient;import org.springframework.web.bind.annotation.GetMapping;/** * @author billjiang [e-mail] * @create 17-8-23 */@FeignClient(value="hello")public interface HelloService {    @GetMapping("/message")    HelloMessage hello();}

被调用接口WorldService

package com.example.helloworldfeign.service;import com.example.helloworldfeign.model.WorldMessage;import org.springframework.cloud.netflix.feign.FeignClient;import org.springframework.web.bind.annotation.GetMapping;/** * @author billjiang [e-mail] * @create 17-8-23 */@FeignClient(value="world")public interface WorldService {    @GetMapping("/message")    WorldMessage world();}

入口类HelloworldController：

package com.example.helloworldfeign.controller;import com.example.helloworldfeign.model.HelloMessage;import com.example.helloworldfeign.model.HelloworldMessage;import com.example.helloworldfeign.model.WorldMessage;import com.example.helloworldfeign.service.HelloService;import com.example.helloworldfeign.service.WorldService;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RestController;/** * @author billjiang [e-mail] * @create 17-8-23 */@RestControllerpublic class HelloworldController {    private static final Logger log = LoggerFactory.getLogger(HelloworldController.class);    private static final String HELLO_SERVICE_NAME = "hello";    private static final String WORLD_SERVICE_NAME = "world";    @Autowired    private HelloService helloService;    @Autowired    private WorldService worldService;    @GetMapping("/")    public String home() {        return "hello world";    }    @GetMapping("/message")    public HelloworldMessage getMessage() {        HelloMessage hello = helloService.hello();        WorldMessage world = worldService.world();        HelloworldMessage helloworld = new HelloworldMessage();        helloworld.setHello(hello);        helloworld.setWord(world);        log.debug("Result helloworld message:{}", helloworld);        return helloworld;    }}

为了更好的地查看效果，hello服务和world服务可以启动多个实例，并把调用实例的ip和端口输出来。