源码:
public class HashTest { private static TreeMap<Long, Node> vNodes; //虚拟节点集合 private static List<Node> rNodes; //真实节点集合 private static final int REAL_NODE_NUM = 5; //真实节点数 private static final int VIRTUAL_NODE_NUM = 100; //虚拟节点数 public static void main(String[] args) { //物理节点 rNodes = new ArrayList<Node>(); for(int i=0; i<REAL_NODE_NUM; i++){ Node node = new Node("192.168.1." + (i+1), (1000+i), ""); rNodes.add(node); } init(); //生成随机数,验证测试数据在真实机器上的数量分布情况 Map<String, Long> map = new HashMap<String, Long>(); for(int i=0; i<1000; i++){ Node node = getNode("key"+i); if(map.containsKey(node.getIp())){ map.put(node.getIp(), new Long(map.get(node.getIp()).longValue() + 1)); }else{ map.put(node.getIp(), new Long(1)); } } //显示数据分布情况 for(Iterator<String> it = map.keySet().iterator(); it.hasNext();){ String ip = it.next(); System.out.println(ip + ": " + map.get(ip)); } } /** * 初始化真实节点和虚拟节点之间的映射关系 */ private static void init() { vNodes = new TreeMap<Long, Node>(); for(int i=0; i<rNodes.size(); i++){ final Node node = rNodes.get(i); for(int j=0; j<VIRTUAL_NODE_NUM; j++){ String hashKey = node.getIp() + "-V-" + j; node.setHashKey(hashKey); vNodes.put(hash(hashKey), node); } } } /** * 获取对应的真实节点对象 * @param key * @return */ public static Node getNode(String key) { Node node = null; SortedMap<Long, Node> tail = vNodes.tailMap(hash(key)); if(tail.size() == 0){ node = vNodes.get(vNodes.firstKey()); }else{ node = tail.get(tail.firstKey()); } node.setData(key); return node; } /** * 一致性hash算法 * @param key * @return */ private static Long hash(String key) { ByteBuffer buf = ByteBuffer.wrap(key.getBytes()); int seed = 0x1234ABCD; ByteOrder byteOrder = buf.order(); buf.order(ByteOrder.LITTLE_ENDIAN); long m = 0xc6a4a7935bd1e995L; int r = 47; long h = seed ^ (buf.remaining() * m); long k; while (buf.remaining() >= 8) { k = buf.getLong(); k *= m; k ^= k >>> r; k *= m; h ^= k; h *= m; } if (buf.remaining() > 0) { ByteBuffer finish = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN); // for big-endian version, do this first: // finish.position(8-buf.remaining()); finish.put(buf).rewind(); h ^= finish.getLong(); h *= m; } h ^= h >>> r; h *= m; h ^= h >>> r; buf.order(byteOrder); return h; } }