负载均衡算法之轮询

轮询顾名思义就是按照顺序进行轮流访问
实现算法如下：

public class RoundRobin {    //初始化全局变量，记录上次调用过得机器    public static int j;    static int[] servers = {1,2,3,4,5,6,7,8,9,10};    public static void main(String[] args) {        while(true){            try {                Thread.sleep(100);                System.out.println(getServer());            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }    public static String getServer(){        //初始化服务器            //上次调用机器+1取模            j = (j+1)%servers.length;            return "s"+j;    }}

但是由于线上服务器由于配置或者非单一服务等原因，服务性能可能不一致，所以均等轮询策略满足不了需求，就有了加权轮询算法：
三台机器S[i] = {1,2,3}，那么分配的权重可能是{2,4,6},那么访问算法如下：
import java.util.ArrayList;
import java.util.List;

public class WeightRoundRobin {

/**上次选择的服务器*/  private int currentIndex = -1;  /**当前调度的权值*/  private int currentWeight = 0;  /**最大权重*/  private int maxWeight;  /**权重的最大公约数*/  private int gcdWeight;  /**服务器数*/  private int serverCount;  private List<Server> servers = new ArrayList<Server>(); /* * 得到两值的最大公约数 */public int greaterCommonDivisor(int a, int b){      if(a % b == 0){        return b;    }else{        return greaterCommonDivisor(b,a % b);    }}/* * 得到list中所有权重的最大公约数，实际上是两两取最大公约数d，然后得到的d * 与下一个权重取最大公约数，直至遍历完 */public int greatestCommonDivisor(List<Server> servers){      int divisor = 0;      for(int index = 0, len = servers.size(); index < len - 1; index++){          if(index ==0){              divisor = greaterCommonDivisor(                          servers.get(index).getWeight(), servers.get(index + 1).getWeight());          }else{              divisor = greaterCommonDivisor(divisor, servers.get(index).getWeight());          }      }      return divisor;  }/* * 得到list中的最大的权重 */public int greatestWeight(List<Server> servers){      int weight = 0;      for(Server server : servers){          if(weight < server.getWeight()){              weight = server.getWeight();          }      }      return weight;  }/**  *  算法流程：   *  假设有一组服务器 S = {S0, S1, …, Sn-1}  *  有相应的权重，变量currentIndex表示上次选择的服务器  *  权值currentWeight初始化为0，currentIndex初始化为-1 ，当第一次的时候返回 权值取最大的那个服务器，  *  通过权重的不断递减 寻找 适合的服务器返回 */   public Server getServer(){       while(true){           currentIndex = (currentIndex + 1) % serverCount;           if(currentIndex == 0){               currentWeight = currentWeight - gcdWeight;               if(currentWeight <= 0){                   currentWeight = maxWeight;                   if(currentWeight == 0){                       return null;                   }               }           }           if(servers.get(currentIndex).getWeight() >= currentWeight){               return servers.get(currentIndex);           }       }   }  public void init(){       servers.add(new Server("192.168.191.1", 1));       servers.add(new Server("192.168.191.2", 2));       servers.add(new Server("192.168.191.4", 4));       servers.add(new Server("192.168.191.8", 8));       maxWeight = greatestWeight(servers);       gcdWeight = greatestCommonDivisor(servers);       serverCount = servers.size();   }   public static void main(String args[]){      WeightRoundRobin weightRoundRobin = new WeightRoundRobin();        weightRoundRobin.init();        for(int i = 0; i < 15; i++){            Server server = weightRoundRobin.getServer();            System.out.println("server " + server.getIp() + " weight=" + server.getWeight());        }   }

}

class Server{
private String ip;
private int weight;

 public Server(String ip, int weight) {       this.ip = ip;       this.weight = weight;   }public String getIp() {    return ip;}public void setIp(String ip) {    this.ip = ip;}public int getWeight() {    return weight;}public void setWeight(int weight) {    this.weight = weight;}  

}