第 5 周作业

package hash;

import java.util.SortedMap;
import java.util.TreeMap;

public class ConsistentHash {

	private static String[] servers = { "192.168.0.1", "192.168.0.2", "192.168.0.3", "192.168.0.4", "192.168.0.5" };

	private static SortedMap<Integer, String> virtualNodes = new TreeMap<Integer, String>();

	private static final int VIRTUAL_NODE_NUMBER = 150;
	private static final String VIRUTAL_NODE_SPIT_STRING = "#";

	static {
		for (int i = 0; i < servers.length; i++) {
			String server = servers[i];

			for (int j = 0; j < VIRTUAL_NODE_NUMBER; j++) {
				String virtualNode = server + VIRUTAL_NODE_SPIT_STRING + j;
				int hashCode = getHash(virtualNode);

				virtualNodes.put(hashCode, virtualNode);// server);
			}
		}
	}

	// FNV1_32_HASH
	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);
			hash = hash & Integer.MAX_VALUE;
		return hash;
	}

	public static String getServer(String key) {
		int hashCode = getHash(key);

		SortedMap<Integer, String> tailMap = virtualNodes.tailMap(hashCode);
		String virtualNode;

		if (!tailMap.isEmpty()) {
			virtualNode = tailMap.get(tailMap.firstKey());
		} else {
			virtualNode = virtualNodes.get(virtualNodes.firstKey());
		}

		if (virtualNode != null && !virtualNode.isEmpty()) {
			String server = virtualNode.substring(0, virtualNode.indexOf(VIRUTAL_NODE_SPIT_STRING));
			return server;
		}
		return null;

	}

}