概述

在第二篇文章SpringCloud服务调用之Feign中，我们介绍了SpringCloud中使用feign进行服务调用的案例。当时还介绍了feign是基于ribbon的。

这一篇，我们就来看看通过原生的ribbon是怎么进行服务调用的。

官方文档：https://projects.spring.io/spring-cloud/spring-cloud.html#spring-cloud-ribbon

Ribbon is a client side load balancer which gives you a lot of control over the behaviour of HTTP and TCP clients. Feign already uses Ribbon, so if you are using @FeignClient then this section also applies.

ribbon可以实现服务调用和负载均衡，而feign集成了ribbon。

也就是说：feign是基于ribbon的，ribbon的调用可以理解是SpringCloud原生的服务调用。

注：这一篇，我们基于上一篇SpringCloud服务注册之Consul中的consul来实现这么一个demo。

需要：consul、service-producer服务（引入consul）、service-consumer服务（引入consul和ribbon）

版本：SpringBoot 2.0.7.RELEASE与SpringCloud Finchely.RELEASE

一、service-producer

服务生产者与上一节相同，需要引入consul-discovery:

        <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.RELEASE</spring-cloud.version>
    </properties>

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

        <!-- 引入consul用于服务注册与发现 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-consul-discovery</artifactId>
        </dependency>

        <!-- 健康监控 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

配置文件：

server:
  port: 8200
spring:
  application:
    name: service-producer
  cloud:
    consul:
      host: localhost
      port: 8500
      discovery:
        register: true
        instance-id: ${spring.application.name}:${server.port}
        service-name: ${spring.application.name}
        port: ${server.port}

启动类添加@EnableDiscoveryClient注解：

package com.example.serviceproducer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@SpringBootApplication
@EnableDiscoveryClient
public class ServiceProducerApplication {

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

}

测试接口：

package com.example.serviceproducer;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping(value = "producer")
public class HelloAction {

    @GetMapping(value = "hello/{name}")
    public String hello(@PathVariable String name) {
        return "Hello " + name + ", this is response from hello by service-producer.";
    }
}

启动服务后，测试一下：

ribbon-producer.png

二、service-consumer

服务消费者需要引入consul-discovery和netflix-ribbon:

        <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.RELEASE</spring-cloud.version>
    </properties>

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

        <!-- 引入consul用于服务注册与发现 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-consul-discovery</artifactId>
        </dependency>

        <!-- 健康监控 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

        <!-- 引入ribbon -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
        </dependency>

    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

配置文件与service-producer基本相同：

server:
  port: 8201
spring:
  application:
    name: service-consumer
  cloud:
    consul:
      host: localhost
      port: 8500
      discovery:
        register: true
        service-name: ${spring.application.name}
        instance-id: ${spring.application.name}:${server.port}
        port: ${server.port}

同样在启动类上添加@EnableDiscoveryClient注解。

下面就有所不同了，还需要注入一个RestTemplate的Bean实例——这个类来自spring-boot-starter-web包：

package com.example.serviceconsumer;

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.cloud.netflix.hystrix.EnableHystrix;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
@EnableDiscoveryClient
public class ServiceConsumerApplication {

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

    /**
     * 注入RestTemplate Bean并开启负载均衡
     * @return
     */
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

}

注：也可以不采用注入而在使用的时候直接new RestTemplate()。

看一下我编写的测试接口：

package com.example.serviceconsumer;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@RestController
@RequestMapping(value = "consumer")
public class ConsumerAction {

    @Autowired
    private RestTemplate restTemplate;

    @GetMapping(value = "test")
    public String test(String name) {
        // 利用RestTemplate，直接请求对应的service-name/request
        String producerRes = restTemplate.getForObject("http://service-producer/producer/hello/" + name, String.class);
        String res = "service-consumer服务调用service-producer服务，hello接口返回数据：" + producerRes;
        System.out.println(res);
        return res;
    }
}

上面的示例中，使用了restTemplate.getForObject("http://service-producer/producer/hello/" + name, String.class);来调用服务service-producer的路径为producer/hello/{name}的接口。

扩展：ribbon/feign/http比较

与普通的HTTP请求比较：HTTP请求使用http://ip:port/path的方式请求，而ribbon则使用http://service-name/path的方式。

与feign请求比较：

@FeignClient(name = "service-provider")
public interface HelloRemote {

    @GetMapping(value = "hello/{name}")
    public String hello(@PathVariable("name") String name);
}

feign是使用@FeignClient来声明式地声明一个与被调用服务接口相同的接口，然后直接调用这个接口。而ribbon是直接通过路径调用。

四、测试

启动service-consumer后，看一下consul：

ribbon-consul.png

测试consumer服务调用producer服务：

ribbon-consumer.png

至此，基于ribbon进行服务调用的示例已经完成。具体可以参考下面地址的源码。

五、项目源码

https://github.com/laolunsi/spring-cloud-examples/tree/master/04-ServiceConsumeRibbon

参考

1. 方志朋-服务消费者（rest+ribbon）(Finchley版)https://blog.csdn.net/forezp/article/details/81040946

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