第五周作业 1

package arch.study;
import java.util.LinkedList;
import java.util.List;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.HashMap;
import java.util.ArrayList;
import java.util.UUID;
public class ConsistentHash {
    //待添加入Hash环的服务器列表
    private static String[] servers = {"192.168.0.0:111", "192.168.0.1:111", "192.168.0.2:111",
            "192.168.0.3:111", "192.168.0.4:111", "192.168.0.5:111", "192.168.0.6:111", "192.168.0.7:111",
            "192.168.0.8:111", "192.168.0.9:111"};
    private static List<String> realNodes = new LinkedList<>();
    private static SortedMap<Integer, String> virtualNodes = new TreeMap<>();
    private static final int VIRTUAL_NODES = 100;
    static{
        for(int i = 0; i < servers.length; i++)
            realNodes.add(servers[i]);
        for (String str : realNodes){
            for(int i = 0; i < VIRTUAL_NODES; i++){
                String virtualNodeName = str + "&&VN" + String.valueOf(i);
                int hash = getHash(virtualNodeName);
                System.out.println("虚拟节点[" + virtualNodeName + "]被添加, hash值为" + hash);
                virtualNodes.put(hash, virtualNodeName);
            }
        }
        System.out.println();
    }
    //使用FNV1_32_HASH算法计算服务器的Hash值,这里不使用重写hashCode的方法，最终效果没区别
    private static int getHash(String str){
        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;
    }
    private static String getServer(String key){
        int hash = getHash(key);
        SortedMap<Integer, String> subMap = virtualNodes.tailMap(hash);
        String virtualNode;
        if(subMap.isEmpty()){
            Integer i = virtualNodes.firstKey();
            virtualNode = virtualNodes.get(i);
        }else{
            Integer i = subMap.firstKey();
            virtualNode = subMap.get(i);
        }
        return virtualNode.substring(0, virtualNode.indexOf("&&"));
    }
    public static void main(String[] args){
        List<String> invocations = new ArrayList<>();
        for (int i = 0; i < 1000000; i++) {
            invocations.add(UUID.randomUUID().toString());
        }
        HashMap<String, Long> atomicLongMap = new HashMap();
        for (String server : realNodes) {
            atomicLongMap.put(server, 0L);
        }
        for (String invocation : invocations) {
            String selectedServer = getServer(invocation);
            atomicLongMap.put(selectedServer, atomicLongMap.get(selectedServer) + 1);
        }
        System.out.println(StatisticsUtil.standardDeviation(atomicLongMap.values().toArray(new Long[]{})));
    }
}

package arch.study;
public class StatisticsUtil {
    // 方差 s^2=[(x1-x)^2 +...(xn-x)^2]/n
    public static double variance(Long[] x) {
        int m = x.length;
        double sum = 0;
        for (int i = 0; i < m; i++) {// 求和
            sum += x[i];
        }
        double dAve = sum / m;// 求平均值
        double dVar = 0;
        for (int i = 0; i < m; i++) {// 求方差
            dVar += (x[i] - dAve)* (x[i] - dAve);
        }
        return dVar / m;
    }
    // 标准差σ=sqrt(s^2)
    public static double standardDeviation(Long[] x) {
        double variance_value = variance(x);
        return Math.sqrt(variance_value);
    }
}