springcloud-服务调用篇（ribbon）

一、场景描述

我们的微服务已经注册到了注册中心，不同的服务之间如何进行调用？这里我们采用feign或者ribbon都可以实现

二、ribbon实现

1. Idea-->file-->new-->project-->spring initializr-->next-->修改必要信息-->next
2. 分别选择Cloud Routing-->Ribbon
3. 再选择 Cloud Discovery-->Eureka Discovery
4. 使用ribbon我们需要使用restTemplete，需要web支持，选择Web-->web
5. 点击next-->finish
6. 查看生成的pom文件如下

<?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.example</groupId>
    <artifactId>eurekaribbon</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>eurekaribbon</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.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>Finchley.SR1</spring-cloud.version>
    </properties>

    <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>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>

5.我们摘出我们需要的依赖，一个是启用eureka，一个是引入ribbon，一个是引入Web，

<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>

6. application.properties文件中添加eureka配置

spring.application.name=eurekaribbon
server.port=8085
eureka.client.serviceUrl.defaultZone=http://eureka1:8001/eureka/ ,http://eureka1:8002/eureka/,http://eureka1:8003/eureka/

7. 启动类添加 @EnableDiscoveryClient
8. 启动类中添加restTemplete Bean，完整的启动类如下

package com.example.eurekaribbon;

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

9. 这样我们就可以基于ribbon来调用其他服务了，重点是restTemplete上面的@LoadBalanced注解
10. 我们可以简单写一个调用DEMO的hello服务的实现方式如下：

package com.example.eurekaribbon;

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

import javax.annotation.Resource;
@RestController
public class Hello {
    @Resource
    RestTemplate restTemplate;
    @RequestMapping(value = "/hello")
    public  String hello(){
            return restTemplate.getForObject("http://DEMO/hello",String.class);
    }
}

==这里我们引入的RestTemplete是我们在启动类中定义的以@LoadBalanced注解的bean。默认使用的就是ribbon，已经支持负载均衡==

11. 我们可以把注册中心，demo服务启动，再启动现有的ribbon服务。调用localhost:8085/hello。得到返回值helloWord