架构师第 5 周 - 作业

public class HashVirtualNode {
    // 服务器列表10台服务器
    private static String[] servers = {"server0", "server1", "server2",
            "server3", "server4", "server5", "server6", "server7", "server8","server9"};
    // 每个服务器节点对应的虚拟节点个数
    private static final int VIRTUAL_NODES = 1;
    private static List<String> realNodes = new LinkedList<String>();
    private static SortedMap<Integer, String> virtualNodes = new TreeMap<Integer, String>();
    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);
                virtualNodes.put(hash, virtualNodeName);
            }
        }
    }
    /**
     * 计算Hash值
     * @param str
     * @return
     */
    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;
        if (hash < 0)
            hash = Math.abs(hash);
        return hash;
    }
    /**
     * 根据key得到应当路由到的结点
     * @param key
     * @return
     */
    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);
        }
        if(StringUtils.isNotBlank(virtualNode)) {
            return virtualNode.substring(0, virtualNode.indexOf("_"));
        }
        return null;
    }
}

public static void main(String[] args) {
        int[] serverNum = new int[10];
        for(int i=1; i<=1000000; i++) {
            switch (getServer(String.valueOf(i))) {
                case "server0" :
                    serverNum[0]++;
                    break;
                case "server1" :
                    serverNum[1]++;
                    break;
                case "server2" :
                    serverNum[2]++;
                    break;
                case "server3" :
                    serverNum[0]++;
                    break;
                case "server4" :
                    serverNum[0]++;
                    break;
                case "server5" :
                    serverNum[0]++;
                    break;
                case "server6" :
                    serverNum[0]++;
                    break;
                case "server7" :
                    serverNum[0]++;
                    break;
                case "server8" :
                    serverNum[0]++;
                    break;
                case "server9" :
                    serverNum[0]++;
                    break;
                default:
                    return;
            }
        }
       double result = getStandardDevition(serverNum);
       System.out.println("标准方差结果为：" + result);
    }
    /**
     * 根据标准方差计算方式计算
     * @param arr
     * @return
     */
    public static double getStandardDevition(int[] arr) {
        double sum = 0;
        // 平均应是每个服务器存放10万个KV值
        double avgValue = 100000;
        int number = arr.length;
        for (int i = 0; i < number; i++) {
            System.out.println("server" + i + "存放KV 数据个数： " + arr[i]);
            sum += Math.pow((arr[i] - avgValue), 2);
        }

        return Math.sqrt((sum / (number - 1)));
    }