架构师训练营 - 第五周

package com.infoq.week5;
import java.util.List;import java.util.SortedMap;import java.util.TreeMap;
public class ConsistentHashing {
    private static final int VIRTUAL_NODES = 150;
    private List<String> serverList = null;
    private SortedMap<Integer, String> virtualNodes = new TreeMap<Integer, String>();        public ConsistentHashing(){            }
    public ConsistentHashing(List serverList) {        this.serverList = serverList;    }
    public void addServer(String serverName) {        this.serverList.add(serverName);    }
    public void buildNodes() {        for (String str : serverList) {            for(int i = 0; i < VIRTUAL_NODES; i++){                String virtualNodeName = str + "-VNode-" + String.valueOf(i);                int hash = getHash(virtualNodeName);                virtualNodes.put(hash, virtualNodeName);            }        }    }
    public String getServerName(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(null != virtualNode){            return virtualNode.substring(0, virtualNode.indexOf("-VNode"));        }        return null;    }
    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;    }    }