架构师训练营第五周课后作业

import java.util.List;
import java.util.Set;
import java.util.HashSet;
import java.util.TreeMap;
import java.util.SortedMap;
public class ConsistentHashService {
  final private static long ring = 1L << 32;
  private int virtualNodeNums = 10;
  private HashSet<String> servers;
  private TreeMap<Long, String> nodeHashMap;
  
  public ConsistentHashService() {
    servers = new HashSet<>();
    nodeHashMap = new TreeMap<>();
  }
  public void setVirtualNodeNum(int nodeNum) {
    this.virtualNodeNums = nodeNum;
  }
  public void addServers(List<String> serverList) {
    int serverCount = servers.size();
    for(String server : serverList) {
      servers.add(server);
    }
    if(serverCount != servers.size()) {
      rebuildVirtualNodes();
    }
  }
  public void removeServers(List<String> serverList) {
    int serverCount = servers.size();
    for(String server : serverList) {
      servers.remove(server);
    }
    if(serverCount != servers.size()) {
      rebuildVirtualNodes();
    }
  }
  public void rebuildVirtualNodes() {
    TreeMap<Long, String> newHashMap = new TreeMap<>();
    for(String server : servers) {
      for(int i = 0; i < virtualNodeNums; i++) {
        String v = server + "__VN__" + i;
        Long hash = getHash(v) % ring;
        // System.out.println(hash + ":" + server);
        newHashMap.put(hash, server);
      }
    }
    nodeHashMap = newHashMap;
  }
  private Long getHash(String key) {
    final int p = 16777619;
    Long hash = 2166136261L;
    for (int idx = 0, num = key.length(); idx < num; ++idx) {
        hash = (hash ^ key.charAt(idx)) * 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;
  }
  public String getServer(String key) {
    Long keyHash = getHash(key) % ring;
    SortedMap<Long, String> tailMap = nodeHashMap.tailMap(keyHash);
    Long nodeHash = tailMap.isEmpty() ? nodeHashMap.firstKey() : tailMap.firstKey();
    return nodeHashMap.get(nodeHash);
  }
}