第五周 - 作业

package com.leo.homework;
import cn.hutool.core.util.HashUtil;
import org.springframework.util.CollectionUtils;
import org.springframework.util.StringUtils;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
public class ConsistentHashingWithoutVirtualNode {
  private static final String[] servers = {
    "192.168.0.0",
    "192.168.0.1",
    "192.168.0.2",
    "192.168.0.3",
    "192.168.0.4",
    "192.168.0.5",
    "192.168.0.6",
    "192.168.0.7",
    "192.168.0.8",
    "192.168.0.9",
    "192.168.0.10"
  };
  private static final List<String> realNodes = new LinkedList<>();
  private static final Map<String, Integer> numOfNodes = new HashMap<>(servers.length);
  private static final SortedMap<Integer, String> virtualNodes = new TreeMap<>();
  private static final int VIRTUAL_NODES = 5;
  static {
    Collections.addAll(realNodes, servers);
    for (String str : realNodes) {
      for (int i = 0; i < VIRTUAL_NODES; i++) {
        String virtualNodeName = str + "&&VN" + i;
        int hash = HashUtil.fnvHash(virtualNodeName);
        virtualNodes.put(hash, virtualNodeName);
      }
    }
  }
  public static void main(String[] args) {
    List<String> testKey = getTestKey(1000000);
    for (String key : testKey) {
      String server = getServer(HashUtil.fnvHash(key));
      numOfNodes.put(server, numOfNodes.getOrDefault(server, 0) + 1);
    }
    Collection<Integer> values = numOfNodes.values();
    if (CollectionUtils.isEmpty(values)) return;
    double avg = values.stream().mapToInt(Integer::intValue).average().orElse(0);
    int total = values.stream().mapToInt(value -> (int) ((value - avg) * (value - avg))).sum();
    System.out.println("数据在服务器上分布数量的标准差: " + Math.sqrt(total * 1.0 / values.size()));
  }
  
    private static String getServer(int hashKey) {
    SortedMap<Integer, String> subMap = virtualNodes.tailMap(hashKey);
    String virtualNode =
        subMap.isEmpty()
            ? virtualNodes.get(virtualNodes.firstKey())
            : subMap.get(subMap.firstKey());
    return StringUtils.hasText(virtualNode)
        ? virtualNode.substring(0, virtualNode.indexOf("&&"))
        : null;
  }
  private static List<String> getTestKey(int num) {
    return IntStream.range(0, num)
        .mapToObj(i -> UUID.randomUUID().toString())
        .collect(Collectors.toList());
  }
}