权重选择算法Java实现

 我们有时候会遇到这种需求，那就是根据权重，按照比例去获取相应的信息，比如配置信息获取，负载均衡RS获取等。

 在此就举一个例子，然后简单的实现。

需求：后端有三台机器，信息分别为，

S1<ip:"10.0.0.1",port:8081,weight:20>,

S2<ip:"10.0.0.2",port:8082,weight:40>, 

S3<ip:"10.0.0.3",port:8083,weight:60>，

根据weight按照比例返回响应的机器信息。

   算法思路：将三个权重映射到一个一维空间中，那么S1对应区间[0, 20), S2对应区间[20, 60), [60, 120]，然后在[0,120]之间生成随机数，看此数落在哪个区间，那么就返回对应机器的信息。

talk is cheap, show me the code:

private int getServerByWeight(int[] weightArr) {    int[][] randArr = new int[weightArr.length][2];    int totalRank = 0;    int index = 0;    for(int i=0;i<weightArr.length;i++) {        if (weightArr[i] <= 0) {            continue;        }        totalRank += weightArr[i];        randArr[i][0] = i;        randArr[i][1] = totalRank;    }    int hitRank = new Random().nextInt(totalRank) + 1;//[1, totalRand]    for (int i = 0; i < randArr.length; i++) {        if (hitRank <= randArr[i][1]) {            return randArr[i][0];        }    }    return randArr[0][0];}public Server choose(List<Server> serverList) {    if (null == serverList) {        return null;    }    int[] weightArr = new int[serverList.size()];    for(int i = 0; i < serverList.size(); i++) {        if (serverList.get(i).getWeight() > 0) {            weightArr[i] = serverList.get(i).getWeight();        }    }    if (weightArr.length == 0) {        return null;    }    int chosenIndex = getServerByWeight(weightArr);    return serverList.get(chosenIndex);}

主要有两个函数：choose和getServerByWeight。测试代码如下：

WeightAllocationAlg.java:

import java.util.Arrays;import java.util.List;import java.util.Random;import java.util.concurrent.atomic.AtomicInteger;/** * Created by iqiyi on 2017/10/17. */class Server {    private String ip;    private int port;    private int weight;    public Server(String ip, int port, int weight) {        this.ip = ip;        this.port = port;        this.weight = weight;    }    public String getIp() {        return ip;    }    public void setIp(String ip) {        this.ip = ip;    }    public int getPort() {        return port;    }    public void setPort(int port) {        this.port = port;    }    public int getWeight() {        return weight;    }    public void setWeight(int weight) {        this.weight = weight;    }    public String toString() {        return "ip : " + ip + ", port : " + port + ", weight : " + weight;    }}public class WeightAllocationAlg {    private AtomicInteger[] completedCount = new AtomicInteger[3];    public WeightAllocationAlg() {        completedCount[0] = new AtomicInteger(0);        completedCount[1] = new AtomicInteger(0);        completedCount[2] = new AtomicInteger(0);    }    private int getServerByWeight(int[] weightArr) {        int[][] randArr = new int[weightArr.length][2];        int totalRank = 0;        int index = 0;        for(int i=0;i<weightArr.length;i++) {            if (weightArr[i] <= 0) {                continue;            }            totalRank += weightArr[i];            randArr[i][0] = i;            randArr[i][1] = totalRank;        }        int hitRank = new Random().nextInt(totalRank) + 1;//[1, totalRand]        for (int i = 0; i < randArr.length; i++) {            if (hitRank <= randArr[i][1]) {                return randArr[i][0];            }        }        return randArr[0][0];    }    public Server choose(List<Server> serverList) {        if (null == serverList) {            return null;        }        int[] weightArr = new int[serverList.size()];        for(int i = 0; i < serverList.size(); i++) {            if (serverList.get(i).getWeight() > 0) {                weightArr[i] = serverList.get(i).getWeight();            }        }        if (weightArr.length == 0) {            return null;        }        int chosenIndex = getServerByWeight(weightArr);        return serverList.get(chosenIndex);    }    public void doTestConcurrently(final List<Server> servers, int threadCount) {        class MyRunnable implements Runnable {            public void run() {                Server svr  = choose(servers);                if (svr.getIp().equals("10.0.0.1")) {                    completedCount[0].incrementAndGet();                } else if (svr.getIp().equals("10.0.0.2")) {                    completedCount[1].incrementAndGet();                } else if(svr.getIp().equals("10.0.0.3")) {                    completedCount[2].incrementAndGet();                }            }        }        try {            Thread [] ts = new Thread[threadCount];            for (int i=0; i<threadCount; i++) {                ts[i] = new Thread(new MyRunnable());            }            for (int i = 0; i < threadCount; i++) {                ts[i].start();            }            for (int i = 0; i < threadCount; i++) {                ts[i].join();            }        } catch (Exception ex) {            ex.printStackTrace();        } finally {            int totalCompleted = completedCount[0].get() + completedCount[1].get() + completedCount[2].get();            if (totalCompleted == threadCount) {                System.out.println((double)completedCount[0].get()/totalCompleted);                System.out.println((double)completedCount[1].get()/totalCompleted);                System.out.println((double)completedCount[2].get()/totalCompleted);            }        }    }    public static void main(String[] args) {        Server[] servers = {                new Server("10.0.0.1", 8081, 20),                new Server("10.0.0.2", 8082, 40),                new Server("10.0.0.3", 8083, 60)        };        WeightAllocationAlg weightAllocationAlg = new WeightAllocationAlg();        Server server = weightAllocationAlg.choose(Arrays.asList(servers));        System.out.println(server.toString());        int threadCount = 100;        weightAllocationAlg.doTestConcurrently(Arrays.asList(servers), threadCount);    }}

结果如下：

ip : 10.0.0.2, port : 8082, weight : 40
0.18
0.34
0.48

可以看到基本上是按照1:2:3的比例返回的，跟预期的一致，当然略有偏差，如果在数据量大且随机函数分布较均匀的情况下结果应该就是按照1:2:3来的。

Author：忆之独秀

Email：[e-mail]

注明出处：http://blog.csdn.net/lavorange/article/details/78320349