一、手写随机负载均衡

    1、引入依赖

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


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

    2、controller定义

@Resource
private RestTemplate restTemplate;

@Resource
private DiscoveryClient discoveryClient;

@RequestMapping("/restLoadbalance")
public String manualLoadBlance(){
    //1、获取order服务urls
    List<ServiceInstance> instances = this.discoveryClient.getInstances("order");
    List<String> urls = instances.stream().map(instance->instance.getUri().toString()+"/order/query").collect(Collectors.toList());

    //2、随机负载请求
    int index = ThreadLocalRandom.current().nextInt(urls.size());
    return this.restTemplate.getForObject(urls.get(index),String.class);
}

二、LoadBalancer

      

    2.1、API

        （1）、引入依赖

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

        （2）、代码

//2、loadbalancer api
@Resource
private LoadBalancerClient loadBalancerClient;


@RequestMapping("/loadbanlancerapi")
public String loadBanlancerApi(){
    ServiceInstance serviceInstance = this.loadBalancerClient.choose("order");
    return this.restTemplate.getForObject(serviceInstance.getUri().toString()+"/order/query",String.class);
}

    2.2、注解

        （1）、引入依赖   

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

       （2）、自定义@LoadBanlancer注解得RestTemplate

@Bean
@LoadBalanced   // 相当于为restTemplate整合了lb的能力
public RestTemplate restTemplateLoadBalancer(){
    return new RestTemplate();
}

        （3）、controller代码

@Resource
private RestTemplate restTemplateLoadBalancer;
@RequestMapping("/loadbanlanceraop")
public String loadBanlancerAop(){
    return this.restTemplateLoadBalancer.getForObject("http://order/order/query",String.class);
}

三、默认负载算法

    默认轮询负载：RoundRobinLoadBalancer

    更改默认负载算法：Cloud Native Applications

    （1）、自定义负载算法

public class CustomLoadBalancerConfiguration {
    @Bean
    ReactorLoadBalancer<ServiceInstance> randomLoadBalancer(Environment environment,
                                                            LoadBalancerClientFactory loadBalancerClientFactory) {
        String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
        return new RandomLoadBalancer(loadBalancerClientFactory
                .getLazyProvider(name, ServiceInstanceListSupplier.class),
                name);
    }
}

    （2）、启动类增加注解

@SpringBootApplication
@LoadBalancerClients(defaultConfiguration = CustomLoadBalancerConfiguration.class)
public class UserApplicaiton implements ApplicationRunner {
}

四、源码分析

    （1）、RestTemplate流程

    （2）、LoadBalancerClient#choose(String serviceId)