第五章作业

import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import org.apache.commons.lang3.StringUtils;

import java.util.*;
import java.util.stream.Collectors;

public class ConsistentHash {

    //真实节点列表
    private List<String> realNodes = new LinkedList<>();

    //虚拟节点列表
    private SortedMap<Integer, String> sortedMap = new TreeMap<Integer, String>();

    private Map<String, Integer> realNodeKeyNum = Maps.newHashMap();

    /**
     * 初始化
     *
     * @param servers        待添加入Hash环的服务器列表
     * @param virtualNodeNum 虚拟节点数量
     */
    private void init(String[] servers, int virtualNodeNum) {
        //添加真实节点
        realNodeKeyNum = Maps.newHashMap();
        for (int i = 0; i < servers.length; i++) {
            realNodes.add(servers[i]);
            realNodeKeyNum.put(servers[i], 0);
        }
        //添加虚拟节点
        for (String str : realNodes) {
            for (int i = 1; i <= virtualNodeNum; i++) {
                String nodeName = str + "VM" + String.valueOf(i);
                int hash = getHash(nodeName);
                sortedMap.put(hash, nodeName);
//                System.out.println("虚拟节点hash:" + hash + "【" + nodeName + "】放入");
            }
        }
    }

    //得到应当路由到的结点
    private String getServer(String key) {
        //得到该key的hash值
        int hash = getHash(key);
        //得到大于该Hash值的所有Map
        String host;
        SortedMap<Integer, String> subMap = sortedMap.tailMap(hash);
        if (subMap.isEmpty()) {
            //如果没有比该key的hash值大的，则从第一个node开始
            Integer i = sortedMap.firstKey();
            //返回对应的服务器
            host = sortedMap.get(i);
        } else {
            //第一个Key就是顺时针过去离node最近的那个结点
            Integer i = subMap.firstKey();
            //返回对应的服务器
            host = subMap.get(i);
        }
        if (StringUtils.isNotBlank(host)) {
            String realHost = host.substring(0, host.indexOf("VM"));
//            System.out.println(realHost);
            return realHost;
        }
        return null;
    }

    //使用FNV1_32_HASH算法计算服务器的Hash值
    private int getHash(String str) {
//        int hash = str.hashCode();
        final int p = 16777619;
        int hash = (int) 2166136261L;
        for (int i = 0; i < str.length(); i++) {
            hash = (hash ^ str.charAt(i)) * p;
        }
        hash += hash << 13;
        hash ^= hash >> 7;
        hash += hash << 3;
        hash ^= hash >> 17;
        hash += hash << 5;

        // 如果算出来的值为负数则取其绝对值
        if (hash < 0) {
            hash = Math.abs(hash);
        }
        return hash;
    }

    //计算key路由到的节点,计数+1
    public void calcHash(String key) {
        String server = getServer(key);
        realNodeKeyNum.put(server, realNodeKeyNum.get(server) + 1);
    }

    //打印分配到各真实节点的key数量
    public void print() {
        List<Integer> countList = Lists.newArrayList();
        realNodeKeyNum.entrySet().forEach(entrySet -> {
            System.out.println(entrySet.getKey() + ":" + entrySet.getValue());
            countList.add(entrySet.getValue());
        });
        System.out.println("标准差:" + Math.sqrt(listVariance(countList)));
    }

    /**
     * 各节点分配到的key数量
     * @return
     */
    public List<Integer> getKeyNums() {
        return realNodeKeyNum.values().stream().collect(Collectors.toList());
    }

    /**
     * 计算集合的和
     */
    public final static Double listSum(List<?> list) {
        Double sum = new Double(0);
        for (Object o : list) {
            if (o instanceof Integer) {
                Integer number = (Integer) o;
                sum += number;
            } else {
                Double number = (Double) o;
                sum += number;
            }
        }
        return sum;
    }

    /**
     * 计算集合的平均值
     */
    public final static Double listAvg(List<?> list) {
        return listSum(list) / list.size();
    }

    /**
     * 计算集合的方差
     */
    //方差s^2=[(x1-x)^2 +...(xn-x)^2]/n
    public final static Double listVariance(List<?> list) {
        int size = list.size();
        double avg = listAvg(list);
        double variance = 0;

        for (Object o : list) {
            if (o instanceof Integer) {
                Integer number = (Integer) o;
                variance += (number - avg) * (number - avg);
            } else {
                Double number = (Double) o;
                variance += (number - avg) * (number - avg);
            }
        }

        return variance / size;
    }

    /**
     * 计算标准差     标准差=方差开平方根
     */
    public final static Double listStandardDiviation(List<?> list) {
        return Math.sqrt(listVariance(list));
    }

    public static void main(String[] args) {
        int totalKeyNum = 1000000;
        String[] servers = new String[]{"192.168.0.1:8080", "192.168.0.2:8080", "192.168.0.3:8080", "192.168.0.4:8080", "192.168.0.5:8080",
                "192.168.0.6:8080", "192.168.0.7:8080", "192.168.0.8:8080", "192.168.0.9:8080", "192.168.0.10:8080"};
        double minStandardDeviation = 999999;
        int minStandardDeviationVirtualNodeNum = 0;
        for (int virtualNodeNum = 10; virtualNodeNum <= 1000; virtualNodeNum += 10) {
            ConsistentHash consistentHash = new ConsistentHash();
            consistentHash.init(servers, 500);
            for (int i = 0; i < totalKeyNum; i++) {
                consistentHash.calcHash(UUID.randomUUID().toString());
            }
            List<Integer> keyNums = consistentHash.getKeyNums();
            double sqrt = Math.sqrt(listVariance(keyNums));
            if (minStandardDeviation > sqrt) {
                minStandardDeviation = sqrt;
                minStandardDeviationVirtualNodeNum = virtualNodeNum;
            }
            System.out.println("虚拟节点数:" + virtualNodeNum + "，标准差:" + sqrt);
        }

        System.out.println("===最优虚拟节点数:" + minStandardDeviationVirtualNodeNum + "，标准差:" + minStandardDeviation);

    }


}