Ribbon远程调用

　　Ribbon是客户端的负载均衡机制，它有几种负载均衡机制。默认是轮询，我们也可以自定义规则。通过合理的分配网络请求来减小服务器的压力。项目都是注册到eureka服务器上。通过ribbon去调用其他服务。

项目搭建：

1. 导入依赖

   <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version> 
        <relativePath/>
    </parent>
    <!-- springcloud依赖 -->
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Dalston.SR3</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- eureka客户端依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
    </dependencies>

2. 写配置文件

# 项目访问路径前缀
server:
  context-path: /demo

# 设置服务名称,服务会以这个名字注册到eureka服务器上
spring:
  application:
    name: demo

# 设置eureka服务器的注册地址
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

3. 开发服务接口

import javax.servlet.http.HttpServletRequest;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class MyController {

    @RequestMapping("/data")
    public String testData(HttpServletRequest req){
        String url = req.getRequestURL().toString();
        return "提供服务的是: "+url;
    }
}

4. 启动主函数，测试。

import java.util.Scanner;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
@SpringBootApplication
//申明eureka客户端
@EnableEurekaClient
public class Main {

    public static void main(String[] args) {
        //1. 启动main方法,在控制台输入端口号
        Scanner scan = new Scanner(System.in);
        String port = scan.nextLine();
        //项目以输入的端口号启动
        new SpringApplicationBuilder(Main.class).properties("server.port="+port).run(args);
        //2. 启动两次main方法,分别以8080  8081启动,模拟集群的环境    浏览器访问接口测试下。
    }
}

 二：搭建Ribbon项目

1. 导入依赖

   <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version> 
        <relativePath/>
    </parent>
  <!-- springcloud依赖 -->
  <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Dalston.SR3</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- eureka客户端依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
        <!-- ribbon依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-ribbon</artifactId>
        </dependency>
    </dependencies>

2. 配置application.yml文件 

# 指定默认端口
server:
  port: 8083

# 设置服务名称,服务会以这个名字注册到eureka服务器上
spring:
  application:
    name: ribbon

# 设置eureka服务器的注册地址
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

3. 编写controller

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
@RestController
public class Controller {

     @Autowired
     private RestTemplate restTpl;
     
     @RequestMapping("/testRibbon")
     public String testRibbon() {
         String data = restTpl.getForObject("http://demo/demo/data", String.class);
　　　　　 //String data = restTpl.getForObject("http://127.0.0.1:8081/demo/data", String.class);
　　　　　 //User user = restTpl.getForObject("http://demo/demo/user/{id}", User.class,id); return data;
　　 } 
}

4. 编写主函数入口， 配置RestTemplate 

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;
@SpringBootApplication
//申明eureka客户端
@EnableEurekaClient
public class RibbonMain {

    @Bean
    @LoadBalanced
    public RestTemplate getRestTemplate() {
        return new RestTemplate();
    }
    
    public static void main(String[] args) {
        SpringApplication.run(RibbonMain.class, args);
    }
}

测试：我们通过 ribbon来调用其他服务数据，可以看到它默认是走轮询策略。