一、源码分析

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.netflix.loadbalancer;

public interface IRule {
    Server choose(Object var1);

    void setLoadBalancer(ILoadBalancer var1);

    ILoadBalancer getLoadBalancer();
}

轮询负载均衡算法

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.netflix.loadbalancer;

import com.netflix.client.config.IClientConfig;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class RoundRobinRule extends AbstractLoadBalancerRule {
    private AtomicInteger nextServerCyclicCounter;
    private static final boolean AVAILABLE_ONLY_SERVERS = true;
    private static final boolean ALL_SERVERS = false;
    private static Logger log = LoggerFactory.getLogger(RoundRobinRule.class);

    public RoundRobinRule() {
        this.nextServerCyclicCounter = new AtomicInteger(0);
    }

    public RoundRobinRule(ILoadBalancer lb) {
        this();
        this.setLoadBalancer(lb);
    }

    public Server choose(ILoadBalancer lb, Object key) {
        if (lb == null) {
            log.warn("no load balancer");
            return null;
        } else {
            Server server = null;
            int count = 0;

            while(true) {
                if (server == null && count++ < 10) {
                    List<Server> reachableServers = lb.getReachableServers();
                    List<Server> allServers = lb.getAllServers();
                    int upCount = reachableServers.size();
                    int serverCount = allServers.size(); //服务器集群总数
                    if (upCount != 0 && serverCount != 0) {
                        int nextServerIndex = this.incrementAndGetModulo(serverCount);
                        server = (Server)allServers.get(nextServerIndex);
                        if (server == null) {
                            Thread.yield();
                        } else {
                            if (server.isAlive() && server.isReadyToServe()) {
                                return server;
                            }

                            server = null;
                        }
                        continue;
                    }

                    log.warn("No up servers available from load balancer: " + lb);
                    return null;
                }

                if (count >= 10) {
                    log.warn("No available alive servers after 10 tries from load balancer: " + lb);
                }

                return server;
            }
        }
    }

    private int incrementAndGetModulo(int modulo) {
        int current;
        int next;
        do {
            current = this.nextServerCyclicCounter.get();
            next = (current + 1) % modulo;
        } while(!this.nextServerCyclicCounter.compareAndSet(current, next));

        return next;
    }

    public Server choose(Object key) {
        return this.choose(this.getLoadBalancer(), key);
    }

    public void initWithNiwsConfig(IClientConfig clientConfig) {
    }
}

二、手写Ribbon轮询算法

package com.george.springcloud.lb;

import org.springframework.cloud.client.ServiceInstance;

import java.util.List;

/**
 * @author Yang Hao
 * @description
 * @date 2020-09-16 14:58
 */
public interface MyLoadBalancer {

    ServiceInstance instances(List<ServiceInstance> serviceInstances);
}

package com.george.springcloud.lb.impl;

import com.george.springcloud.lb.MyLoadBalancer;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.stereotype.Component;

import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @author Yang Hao
 * @description
 * @date 2020-09-16 15:00
 */
@Component //让容器扫描到这个类
public class MyLoadBalancerImpl implements MyLoadBalancer {

    private AtomicInteger atomicInteger = new AtomicInteger(0);

    /**
     * 参考RoundRobinRule 类的源码实现 自定义选择规则
     *
     * @return
     */
    public final int getAndIncrement() {
        int current;
        int next;
        do {
            current = this.atomicInteger.get();
            //Integer 最大值2147483647
            next = current >= 2147483647 ? 0 : current + 1;
        } while (!this.atomicInteger.compareAndSet(current, next));
        System.out.println("---------第几次访问,次数:next=" + next);
        return next;
    }

    /**
     * 负载均衡算法: rest接口第几次请求数%服务器集群总数量=实际调用服务器位置下标.每次服务重启动后rest接口计数从1开始。
     *
     * @param serviceInstances
     * @return
     */
    @Override
    public ServiceInstance instances(List<ServiceInstance> serviceInstances) {
        int index = getAndIncrement() % serviceInstances.size();
        return serviceInstances.get(index);
    }
}

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

不知道这里为啥会报这个错

通过postman请求都是正常的