Spring Cloud 入门教程2、服务消费者（Ribbon）

一、前言

1、什么是Ribbon

Ribbon是Netflix开源的实现了负载均衡等功能的RPC客户端。 支持HTTP、TCP、UDP协议，且有一定的容错、缓存等机制。
Spring Cloud基于Ribbon封装了Spring Cloud Ribbon，方便结合Eureka、Consul等服务治理框架使用。Ribbon的主要作用是：从服务器端拿到对应服务列表后以负载均衡的方式访问对应服务。

从这张图上来说，Ribbon主要是从Eureka拿到服务列表之后，以负载均衡的策略选择其中一台发起调用。
2、本篇环境信息

框架
版本
Spring Boot
2.0.0.RELEASE
Spring Cloud
Finchley.BUILD-SNAPSHOT
JDK
1.8.x

3、准备工作

Eureka服务端搭建
参考：https://ken.io/note/spring-cloud-eureka-quickstart
服务提供者搭建
参考：https://ken.io/note/spring-cloud-eureka-quickstart

项
说明
GroupId
io.ken.springcloud.testservice
ArtifactId
testservice

pom.xml、启动类（App.java）保持不变
二、服务提供者准备

1、配置Eureka地址

application.yml 配置
server:
port: 8602

spring:
application:
name: testservice

eureka:
client:
serviceUrl:
defaultZone: http://localhost:8800/eureka/

app:
ip: localhost
2、DTO准备

创建共用的ResponseDTO：Result.java
package io.ken.springcloud.testservice.model;

public class Result {

private int code;

private String message;

private Object content;

private String serviceName;

private String host;

public int getCode() {
    return code;
}

public void setCode(int code) {
    this.code = code;
}

public String getMessage() {
    return message;
}

public void setMessage(String message) {
    this.message = message;
}

public Object getContent() {
    return content;
}

public void setContent(Object content) {
    this.content = content;
}

public String getServiceName() {
    return serviceName;
}

public void setServiceName(String serviceName) {
    this.serviceName = serviceName;
}

public String getHost() {
    return host;
}

public void setHost(String host) {
    this.host = host;
}

}
创建Plus.java用作加法运算RequestDTO
package io.ken.springcloud.testservice.model;

public class Plus {

private int numA;

private int numB;

public int getNumA() {
    return numA;
}

public void setNumA(int numA) {
    this.numA = numA;
}

public int getNumB() {
    return numB;
}

public void setNumB(int numB) {
    this.numB = numB;
}

}
3、编写服务入口

创建服务入口 TestController.java
package io.ken.springcloud.testservice.controller;

import io.ken.springcloud.testservice.model.Plus;
import io.ken.springcloud.testservice.model.Result;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TestController {

@Value("${spring.application.name}")
private String serviceName;

@Value("${app.ip}")
private String address;

@Value("${server.port}")
private String port;

@RequestMapping("/")
public Object index() {
    Result result = new Result();
    result.setServiceName(serviceName);
    result.setHost(String.format("%s:%s", address, port));
    result.setMessage("hello");
    return result;
}

@RequestMapping("/plus")
public Object plus(Plus plus) {
    Result result = new Result();
    result.setServiceName(serviceName);
    result.setHost(String.format("%s:%s", address, port));
    result.setMessage("success");
    result.setContent(plus.getNumA() + plus.getNumB());
    return result;
}

}
4、访问测试

启动TestService
分别以端口8602,8603启动testservice。 此时testservice等于是在Eureka Server注册了两个实例

分别访问 http://localhost:8602，http://localhost:8603
将会看到以下信息：

http://localhost:8602

{
"code": 0,
"message": "success",
"content": 0,
"serviceName": "testservice",
"host": "localhost:8062"
}

http://localhost:8603

{
"code": 0,
"message": "success",
"content": 0,
"serviceName": "testservice",
"host": "localhost:8063"
}
三、服务消费者搭建（Ribbon）

1、创建Ribbon项目

创建一个Spring Boot工程
使用maven-archtype-quickstart模板创建项目

项
说明
GroupId
io.ken.springcloud.ribbonclient
ArtifactId
ribbonclient

在pom.xml加入相关依赖

4.0.0

<groupId>io.ken.springcloud.ribbonclient</groupId>
<artifactId>ribbonclient</artifactId>
<version>1.0-SNAPSHOT</version>

<name>ribbonclient</name>
<url>http://ken.io</url>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.0.RELEASE</version>
</parent>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>Finchley.BUILD-SNAPSHOT</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>

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

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

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

    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.11</version>
        <scope>test</scope>
    </dependency>

</dependencies>

<repositories>
    <repository>
        <id>spring-snapshots</id>
        <name>Spring Snapshots</name>
        <url>https://repo.spring.io/libs-snapshot</url>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </repository>
</repositories>

<build>
    <finalName>ribbonclient</finalName>
</build>

2、配置Ribbon启动类

配置启动类
修改srcmainjavaiokenspringcloudeurekaserverApp.java 基于Spring Boot创建启动类，添加上 @EnableDiscoveryClient 注解
并且向程序的ioc注入一个bean: restTemplate，并通过@LoadBalanced注解表明这个restRemplate开启负载均衡的功能。
package io.ken.springcloud.ribbonclient;

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;

@EnableDiscoveryClient
@SpringBootApplication
public class App {

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

@Bean
@LoadBalanced
public RestTemplate restTemplate() {
    return new RestTemplate();
}

}
3、编写Eureka服务访问

创建TestService.java
TestService作为访问testservice的代理服务类，通过RestTemplate访问远程testservice，Ribbon会负责把servicename替换成实际要访问的host
package io.ken.springcloud.ribbonclient.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class TestService {

@Autowired
private RestTemplate restTemplate;

public Object index() {
    return restTemplate.getForObject("http://testservice", String.class);
}

public Object plus(int numA, int numB) {
    String url = String.format("http://testservice/plus?numA=%s&numB=%s", numA, numB);
    return restTemplate.getForObject(url, String.class);
}

}
4、编写服务入口

创建TestController
TestController作为访问服务testservice的入口
package io.ken.springcloud.ribbonclient.controller;

import io.ken.springcloud.ribbonclient.service.TestService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TestController {

@Autowired
private TestService testService;

@RequestMapping("/")
public Object index() {
    return "ribbon client";
}

@RequestMapping("/ti")
public Object ti() {
    return testService.index();
}

@RequestMapping("/plus")
public Object plus(@RequestParam("numa") int numA, @RequestParam("numb") int numB) {
    return testService.plus(numA, numB);
}

}
5、配置Eureka Client

在srcmain下创建文件夹resources文件夹并设置为Resources Root
在resources文件夹下创建application.yml文件并配置Eureka Client
server:
port: 8604

spring:
application:
name: ribbonclient

eureka:
client:
serviceUrl:
defaultZone: http://localhost:8800/eureka/
6、服务访问/消费测试

RibonClient项目启动后，访问 http://localhost:8604/ti 会交替显示以下内容
{
"code": 0,
"message": "hello",
"content": null,
"serviceName": "testservice",
"host": "localhost:8602"
}

{
"code": 0,
"message": "hello",
"content": null,
"serviceName": "testservice",
"host": "localhost:8603"
}
四、备注

本篇示例代码
https://github.com/ken-io/springcloud-course/tree/master/chapter-02