簡介

Spring Cloud Ribbon是一個基於Http和TCP的客戶端負載均衡工具，它是基於Netflix Ribbon實現的。它不像服務註冊中心、配置中心、API網關那樣獨立部署，但是它幾乎存在於每個微服務的基礎設施中。理解Ribbon對於我們使用Spring Cloud來講非常的重要，因為負載均衡是對系統的高可用、網絡壓力的緩解和處理能力擴容的重要手段之一。

在Spring Cloud中，有兩種服務調用方式，一種是Ribbon+RestTemplate，另一種是Feign。文本先講解下基於Ribbon+RestTemplate的用法。

當Ribbon與Eureka配合使用時，Ribbon可自動從Eureka Server獲取服務提供者地址列表，並基於負載均衡算法，請求其中一個服務提供者實例。

實現

新建服務spring-cloud-ribbon

pom.xml

<?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.yan</groupId>
    <artifactId>spring-cloud-ribbon</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.0.RELEASE</version>
        <relativePath/>
    </parent>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Finchley.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-ribbon</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>RELEASE</version>
        </dependency>
    </dependencies>

</project>
 

配置

yml

server:
  port: 8004
spring:
  application:
    name: spring-cloud-ribbon
  cloud:
    config:
      discovery:
        enabled: true
        service-id: spring-cloud-config-server
  profiles:
    active: dev
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

啟動類

核心是配有註解@LoadBalanced

package com.yan;

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;

@SpringBootApplication
@Configuration
@EnableDiscoveryClient
public class RibbonApplication {
    public static void main(String[] args) {
        SpringApplication.run(RibbonApplication.class, args);
    }

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

Controller

package com.yan.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.client.RestTemplate;

import java.util.StringJoiner;

@RestController
@RequestMapping("/ribbon")
public class RibbonController {
    private final RestTemplate template;

    @Autowired
    public RibbonController(RestTemplate template) {
        this.template = template;
    }

    @GetMapping("/get")
    public Object get(String svcName, String url, String className) {
        Class<?> clazz = getResponseType(className);
        String uri = getUrl(svcName, url);
        return template.getForObject(uri, clazz);
    }

    @PostMapping("/post")
    public Object post(@RequestParam String svcName, @RequestParam String url, @RequestParam String className, @RequestBody HttpEntity<Object> httpEntity) {
        Class<?> clazz = getResponseType(className);
        String url1 = getUrl(svcName, url);
        return template.postForObject(url1, httpEntity, clazz);
    }

    private Class<?> getResponseType(@RequestParam String className) {
        Class<?> clazz;
        try {
            clazz = Class.forName(className);
        } catch (ClassNotFoundException e) {
            clazz = String.class;
        }
        return clazz;
    }

    private String getUrl(String svcName, String url) {
        StringJoiner stringJoiner = new StringJoiner("/");
        String uri = stringJoiner.add(svcName).add(url).toString().replaceAll("/+", "/");
        return "http://" + uri;
    }

}

測試

假如我有兩個名叫svcA的服務，同時註冊到同一個Eureka上，只是端口號不同，它們都有一個post接口定義如下：

    @PostMapping("/post/{name}")
    public String post(@PathVariable String name, @RequestBody String type) {
        return “name:” + name + “\ntype:” + type;
    }

打開Postman：
發送請求：http://localhost:8004/ribbon/post?svcName=SVCA&url=/post/xixi&className=java.lang.String
Header：{‘Content-Type‘: ‘application/json‘}
Body: {‘raw‘: {
{
"headers": {"Content-Type": ["application/json"]},
"body": "haha"
}
}}

此時正確返回結果:

name:xixi
type:haha

Spring-Cloud-Ribbon學習筆記（一）：入門