第五周作业

public interface ServerNode {
    // 获取节点
    String GetNode(String key);
}

import java.util.LinkedList;
import java.util.List;

public class NodeList {
    public NodeList(){
        for (int i=0; i< Servers.length;i++){
            Nodes.add(Servers[i]);
        }
    }

    private static String[] Servers = {
            "192.168.0.10:1230",
            "192.168.1.10:1234",
            "192.168.2.10:1123",
            "192.168.3.10:1133",
            "192.168.4.10:1223",
            "192.168.5.10:1423",
            "192.168.6.10:1523",
            "192.168.7.10:1263",
            "192.168.8.10:1238",
            "192.168.9.10:1239",
    };

    // 虚拟节点数
    public static final int VIRTUAL_NODES = 100;

    private List<String> Nodes = new LinkedList<String>();

    public List<String>GetNodes(){
        return Nodes;
    }
}

import org.springframework.util.StringUtils;
import java.util.SortedMap;
import java.util.TreeMap;

public class CoincidentHash implements ServerNode{
    private CoincidentHash(){
        for (String str : nodeList.GetNodes()){
            for(int i=0; i<NodeList.VIRTUAL_NODES; i++){
                String virtualNodeName = str + "&&VN" + i;
                int hash = getHash(virtualNodeName);
                System.out.println("虚拟节点[" + virtualNodeName + "]被添加, hash值为" + hash);
                virtualNodes.put(hash, virtualNodeName);
            }
        }
    }

    // 真实节点
    private NodeList nodeList = new NodeList();
    // 虚拟节点，key表示虚拟节点的hash值，value表示虚拟节点的名称
    private static SortedMap<Integer, String> virtualNodes = new TreeMap<Integer, String>();

    @Override
    public String GetNode(String key) {
        // 得到该key的hash值
        int hash = getHash(key);
        // 得到大于该Hash值的所有Map
        SortedMap<Integer, String> subMap = virtualNodes.tailMap(hash);
        String virtualNode;
        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 = virtualNodes.firstKey();
            //返回对应的服务器
            virtualNode = virtualNodes.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
            virtualNode = subMap.get(i);
        }
        //virtualNode虚拟节点名称要截取一下
        if (!(StringUtils.isEmpty(virtualNode))){
            return virtualNode.substring(0, virtualNode.indexOf("&&"));
        }
        return null;
    }

    private static class HashHolder{
        private static CoincidentHash instance = new CoincidentHash();
    }

    public static  CoincidentHash getInstance(){
        return HashHolder.instance;
    }

    // 使用FNV1_32_HASH算法计算服务器的Hash值
    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;
    }
}

import org.apache.commons.lang3.RandomStringUtils;

//计算标准差
    public static double StandardDiviation(double[] 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);
        }
        //reture Math.sqrt(dVar/(m-1));
        return Math.sqrt(dVar/m);
    }

    @Test
    void testCoincidentHash(){
        HashMap<String,Integer> serverArrangement = new HashMap<>();
//        SortedMap<String,Integer> serverArrangement = new TreeMap<>();
        NodeList nodeList = new NodeList();
        for(String node : nodeList.GetNodes()) {
            serverArrangement.put(node,0);
        }

        String key;
        Integer count;
        String keynode;
        for (int i=0;i<1000000;i++){
            key = RandomStringUtils.randomAlphanumeric(10);
            keynode = CoincidentHash.getInstance().GetNode(key);
            if (serverArrangement.containsKey(keynode)) {
                count = serverArrangement.get(keynode) + 1;
                serverArrangement.replace(keynode, count);
            }
        }

        Integer[] counts = new Integer[serverArrangement.size()];
        serverArrangement.values().toArray(counts);
        double[] tmpCounts = new double[counts.length];
        for (int i=0;i<counts.length;i++){
            tmpCounts[i] = (double) counts[i];
        }

        double sd = StandardDiviation(tmpCounts);
        System.out.println(String.format("10个节点，每个节点100个虚拟节点，100万个KV，分布标准差=%.2f",sd));

        serverArrangement.forEach((k,v) -> System.out.println("server:  "+ k+"   keyNumber:  "+v));
    }