SpringCloud-----Ribbon手写轮询算法

1.在服务的消费方提供一个接口

public interface LoadBalancer{
	// serviceInstanceList 为eureka中服务的数量
    ServiceInstance instance(List<ServiceInstance> serviceInstanceList);

}

2.实现接口

@Component    // 注意一定要将其注入到spring容器之中
public class MyLb implements LoadBalancer{
	// 原子类，保证多线程安全，赋予初始化值为0
    private AtomicInteger atomicInteger = new AtomicInteger(0);
	
	// 获取第几次访问
	// 使用 自旋锁  和  CAS 
    private final int getAndIncrement(){
        int current;
        int next;
        do{
            current = this.atomicInteger.get();
            next = current >= Integer.MAX_VALUE ? 0 : current+1;
        }while (!this.atomicInteger.compareAndSet(current,next));
        // CAS  和内存的数据比较，没有更改，则改为期望的值
        return  next;
    }

    @Override
    public ServiceInstance instance(List<ServiceInstance> serviceInstanceList) {
 		// 算法： 实际调用服务器位置下标 = rest 接口第几次请求数 % 服务器集群总个数
        int index = getAndIncrement() % serviceInstanceList.size();
        return serviceInstanceList.get(index);
    }
}

3.Controller接口实现 ，记住注释@LoadBalanced

	public static  final  String PAYMENT_URL = "http://CLOUD-PAYMENT-SERVICE";
	
    @Resource
    private DiscoveryClient discoveryClient;

    @Resource
    private LoadBalancer loadBalanced;
   
	@GetMapping(value = "/consumer/payment/lb")
    public String getPaymentLB(){
        List<ServiceInstance> instances = discoveryClient.getInstances("CLOUD-PAYMENT-SERVICE");
        if(instances == null || instances.size()<=0){
            return null;
        }

        ServiceInstance serviceInstance = loadBalanced.instance(instances);

        URI uri = serviceInstance.getUri();
        return  restTemplate.getForObject(uri+"/payment/lb",String.class);
    }