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<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
    </dependency>
</dependencies>

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server:
  port: 7072
spring:
  application:
    name: order-server
eureka:
  instance:
    prefer-ip-address: true
    instance-id: ${spring.cloud.client.ip-address}:${spring.application.instance_id:${server.port}}
  client:
    service-url:
      defaultZone: http://localhost:7071/eureka/

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package com.battcn;

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.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;

/**
 * @author Levin
 */
@EnableDiscoveryClient
@SpringBootApplication
public class OrderApplication {

    @Configuration
    class MyConfiguration {
        @LoadBalanced
        @Bean
        RestTemplate restTemplate() {
            return new RestTemplate();
        }
    }

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

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package com.battcn.controller;

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.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import java.util.List;

/**
 * @author Levin
 * @since 2018/9/28 0028
 */
@RestController
@RequestMapping("/orders")
public class OrderController {

    private final RestTemplate restTemplate;
    private final DiscoveryClient discoveryClient;

    @Autowired
    public OrderController(RestTemplate restTemplate, DiscoveryClient discoveryClient) {
        this.restTemplate = restTemplate;
        this.discoveryClient = discoveryClient;
    }

    @GetMapping
    public String query() {
        final List<String> services = discoveryClient.getServices();
        for (String service : services) {
            List<ServiceInstance> list = discoveryClient.getInstances(service);
            for (ServiceInstance instance : list) {
                System.out.println(instance.getUri() + "/" + service + " - " + instance.getServiceId());
            }
        }
        return restTemplate.getForObject("http://PRODUCT-SERVER/products", String.class);
    }
}

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用通俗的概念来说，它就是编码与解码操作，还记得 Eureka Server UI 中 Application 吗？ 
编码：根据 spring.application.name 设置 serviceId 
Server ID：PRODUCT-SERVER
Client A ：http://localhost:7073/products
Client B ：http://localhost:7074/products

解码：通过 serviceId 找到对应的客户端，
然后根据客户端配置的负载算法从对应集合中
找出符合当前算法条件的结果，最后拼接出相应的 http 地址即可

解码前：http://PRODUCT-SERVER/products 
那么将 http://PRODUCT-SERVER 替换成 instance.getUri() 内容是不是就出来了
http://localhost:7073/products 和 http://localhost:7074/products

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package com.battcn.config;

import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.RandomRule;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author Levin
 * @since 2018/9/28 0028
 */
@Configuration
public class RibbonRuleConfiguration {

    @Bean
    public IRule ribbonRule() {
        return new RandomRule();
    }
}

@RibbonClient(name = "ribbonRule",configuration = RibbonRuleConfiguration.class)
public class OrderController {

}