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
@SpringBootApplication
public 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;


@RestController
public 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
@EnableDiscoveryClient
public 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 [email protected]
 * @create 17-8-22
 */
@RestController
public 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;
    }


}

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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
@EnableFeignClients
public 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 [email protected]
 * @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 [email protected]
 * @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 [email protected]
 * @create 17-8-23
 */
@RestController
public 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;
    }

}

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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。