SpringCloud教程二: 服务消费者（rest+ribbon）

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http://blog.csdn.net/forezp/article/details/69788938
本文出自方志朋的博客

在上一篇文章，讲了服务的注册和发现。在微服务架构中，业务都会被拆分成一个独立的服务，服务与服务的通讯是基于http restful的。Spring cloud有两种服务调用方式，一种是ribbon+restTemplate，另一种是feign。在这一篇文章首先讲解下基于ribbon+rest。

一、ribbon简介

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.

—–摘自官网

ribbon是一个负载均衡客户端，可以很好的控制http和tcp的一些行为。Feign默认集成了ribbon。

ribbon 已经默认实现了这些配置bean：

IClientConfig ribbonClientConfig: DefaultClientConfigImpl
IRule ribbonRule: ZoneAvoidanceRule
IPing ribbonPing: NoOpPing
ServerList ribbonServerList: ConfigurationBasedServerList
ServerListFilter ribbonServerListFilter: ZonePreferenceServerListFilter
ILoadBalancer ribbonLoadBalancer: ZoneAwareLoadBalancer

二、准备工作

这一篇文章基于上一篇文章的工程，启动eureka-server 工程；然后在eureka-client中加入mysql, jpa等依赖:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

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

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>

在application.yaml文件中加入数据库的配置:

spring:
  application:
    name: eureka-client
  datasource:
    url: jdbc:mysql://192.168.239.234:3306/test
    username: root
    password: 123456
    driver-class-name: com.mysql.jdbc.Driver

新建一个实体:

package com.lying.eurekaclient.orm;

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
@Entity
public class User {

    @GeneratedValue
    @Id
    private Long id;
    private String name;
    private Integer age;

}

新建一个查询的Service:

package com.lying.eurekaclient.service;

import com.lying.eurekaclient.orm.User;
import org.springframework.data.jpa.repository.JpaRepository;

public interface UserService extends JpaRepository<User, Long> {

    User findByName(String name);

}

新建一个controller, 如下:

package com.lying.eurekaclient.controller;

import com.lying.eurekaclient.orm.User;
import com.lying.eurekaclient.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {

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

    @Autowired
    private UserService userService;

    @RequestMapping(value = "/users/{name}", method = RequestMethod.GET)
    public String fetchUserByName(@PathVariable("name") String name) {
        return userService.findByName(name).toString() + ": " + port;
    }

}

数据库和user表自己建

启动eureka-client工程，它的端口为8810；将eureka-client的配置文件的端口改为8811，并启动，这时你会发现：eureka-client在eureka-server注册了2个实例，这就相当于一个小的集群。访问localhost:9999如图所示：

三、建一个服务消费者

重新新建一个spring-boot工程，取名为：service-ribbon;
在它的pom.xml文件分别引入起步依赖spring-cloud-starter-eureka、spring-cloud-starter-ribbon、spring-boot-starter-web，代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.lying</groupId>
    <artifactId>ribbon-service</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>ribbon-service</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.10.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Edgware.SR2</spring-cloud.version>
    </properties>

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

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

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

在工程的配置文件指定服务的注册中心地址为http://localhost:9999/eureka/，程序名称为 ribbon-service，程序端口为9910。配置文件application.yml如下：

server:
  port: 9910
  
spring:
  application:
    name: ribbon-service
    
eureka:
  client:
    service-url: 
      defaultZone: http://localhost:9999/eureka/

在工程的启动类中,通过@EnableDiscoveryClient向服务中心注册；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 com.lying.ribbonservice;

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 RibbonServiceApplication {

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

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

写一个测试类UserService，通过之前注入ioc容器的restTemplate来消费eureka-client服务的“fetchUserByName”接口，在这里我们直接用的程序名替代了具体的url地址，在ribbon中它会根据服务名来选择具体的服务实例，根据服务实例在请求的时候会用具体的url替换掉服务名，代码如下：

package com.lying.ribbonservice.service;

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

@Service
public class UserService {

    @Autowired
    private RestTemplate restTemplate;

    public String getUserInfo(String name) {
        return restTemplate.getForObject("http://eureka-client/users/" + name, String.class);
    }
}

写一个controller，在controller中用调用UserService 的方法，代码如下：

package com.lying.ribbonservice.controller;

import com.lying.ribbonservice.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {

    @Autowired
    private UserService userService;
    
    @RequestMapping(value = "/getUserInfo/{name}", method = RequestMethod.GET)
    public String getUserInfo(@PathVariable("name") String name) {
        return userService.getUserInfo(name);
    }
    
}

在浏览器上多次访问http://localhost:9910/getUserInfo/Lee，浏览器交替显示：

User(id=2, name=Lee, age=23): 8810
User(id=2, name=Lee, age=23): 8811

这说明当我们通过调用restTemplate.getForObject("http://eureka-client/users/" + name, String.class);方法时，已经做了负载均衡，访问了不同的端口的服务实例。

四、此时的架构

一个服务注册中心，eureka server,端口为9999
eureka-client工程跑了两个实例，端口分别为8810、8811，分别向服务注册中心注册
sercvice-ribbon端口为9910, 向服务注册中心注册
当sercvice-ribbon通过restTemplate调用eureka-client的fetchUserByName接口时，因为用ribbon进行了负载均衡，会轮流的调用eureka-client：8810和8811 两个端口的fetchUserByName接口；

源码下载：https://github.com/lyingfromyou/SpringCloudExample

五、参考资料

本文参考了以下：

spring-cloud-ribbon

springcloud ribbon with eureka

服务消费者