SpringCloud -根据服务名获取服务运行实例并进行负载均衡

Nacos注册中心

每个服务启动之后都要向注册中心发送服务注册请求，注册中心可以和各个注册客户端自定义协议实现服务注册和发现。

• pom.xml

        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>

• 启动服务

获取服务实例测试

@EnableDiscoveryClient
@SpringBootApplication
public class Main83
{
    public static void main(String[] args)
    {
        ConfigurableApplicationContext applicationContext = SpringApplication.run(Main83.class, args);

        DiscoveryClient discoveryClient = applicationContext.getBean(DiscoveryClient.class);
        List<ServiceInstance> instances = discoveryClient.getInstances("nacos-payment-provider");
        for (ServiceInstance instance : instances) {
            System.out.println("instance.getHost() = " + instance.getHost());
            System.out.println("instance.getPort() = " + instance.getPort());
        }

        NacosDiscoveryClient nacosDiscoveryClient = applicationContext.getBean(NacosDiscoveryClient.class);
        List<ServiceInstance> serviceInstances = nacosDiscoveryClient.getInstances("nacos-payment-provider");
        for (ServiceInstance instance : serviceInstances) {
            System.out.println("Nacos instance.getHost() = " + instance.getHost());
            System.out.println("instance.getPort() = " + instance.getPort());
        }

        LoadBalancerClient balancerClient = applicationContext.getBean(LoadBalancerClient.class);
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());

    }


}

在引入注册中心相关的依赖后，注册中心的相关API会实现SpringCloud规范，自动给容器中存入DiscoveryClient对象，引入了Nacos，就是NacosDiscoveryClient。通过DiscoveryClient接口提供的能力可以从注册中心实时拉取服务列表。

• 负载均衡实现
  微服务在自动进行服务发现后，进行的是客户端负载均衡，也就是客户端自己维护了一套负载均衡算法，每次请求选择某一台服务器进行请求。

pom.xml

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

LoadBalancerClient balancerClient = applicationContext.getBean(LoadBalancerClient.class);
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());
        System.out.println("balancerClient.choose(\"nacos-payment-provider\").getPort() = " + balancerClient.choose("nacos-payment-provider").getPort());

LoadBalancerClient类会自动使用容器中的DiscoveryClient进行服务的负载均衡。