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EJoker is a CQRS + EventSourcing framwork
package pro.jk.ejoker.common.algorithm;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.List;
import java.util.SortedMap;
import java.util.TreeMap;
/**
* 用TreeMap做虚拟节点环的一致性哈希算法，
* 采用自 https://blog.csdn.net/mae4a8cs/article/details/55000865
* 这篇文章也是转载的，如果你知道，欢迎告诉我原文地址
* @author kimffy
*
* @param
*/
public class ConsistentHashShard {
private TreeMap nodes; // 虚拟节点
private List shards; // 真实机器节点
private final int NODE_NUM = 64; // 每个机器节点关联的虚拟节点个数
public ConsistentHashShard(List shards) {
super();
this.shards = shards;
init();
}
private void init() { // 初始化一致性hash环
nodes = new TreeMap();
for (int i = 0; i != shards.size(); ++i) { // 每个真实机器节点都需要关联虚拟节点
final S shardInfo = shards.get(i);
for (int n = 0; n < NODE_NUM; n++)
// 一个真实机器节点关联NODE_NUM个虚拟节点
nodes.put(hash("SHARD-" + i + "-NODE-" + n), shardInfo);
}
}
public S getShardInfo(String key) {
SortedMap tail = nodes.tailMap(hash(key)); // 沿环的顺时针找到一个虚拟节点
if (tail.isEmpty()) {
return nodes.get(nodes.firstKey());
}
return tail.get(tail.firstKey()); // 返回该虚拟节点对应的真实机器节点的信息
}
/**
* MurMurHash算法，是非加密HASH算法，性能很高，
* 比传统的CRC32,MD5，SHA-1（这两个算法都是加密HASH算法，复杂度本身就很高，带来的性能上的损害也不可避免）
* 等HASH算法要快很多，而且据说这个算法的碰撞率很低. http://murmurhash.googlepages.com/
*/
private 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;
}
}