第五周 作业 1

public class ConsistentHash {	private static ConcurrentSkipListMap<Integer, String> nodes = new ConcurrentSkipListMap();	// 每台机器虚拟节点数默认为 150	private int virtualNumPerNode = 150;
	public ConsistentHash(List<String> nodes, int virtualNumPerNode) {		this.virtualNumPerNode = virtualNumPerNode;		for (String node:nodes) {			addVirtualNodes(node);		}	}
	private void addVirtualNodes(String node) {		for (int i=0; i<this.virtualNumPerNode; i++) {      // 虚拟节点使用 192.168.1.1#1 表示虚拟的第几个节点			String virtualNode = node+"#"+i;			nodes.put(getHash(virtualNode), virtualNode);		}	}	  // 根据 key 找到存储数据的真实机器节点	public String getNode(Object key) {		Integer hashCode = getHash(key);		Map.Entry<Integer, String> entry = nodes.ceilingEntry(hashCode);		if (entry == null) {			entry = nodes.ceilingEntry(0);		}		String virtualNode = entry.getValue();		return virtualNode.substring(0, virtualNode.indexOf("#"));	}	  // 使用FNV1_32_HASH算法计算服务器的Hash值，hash值能大于 2^31	private int getHash(Object object) {		final int p = 16777619;		int hash = (int) 2166136261L;		String string = object.toString();
		for (int i = 0; i < string.length(); i++)			hash = (hash ^ string.charAt(i)) * p;		hash += hash << 13;		hash ^= hash >> 7;		hash += hash << 3;		hash ^= hash >> 17;		hash += hash << 5;
		// 如果算出来的值为负数则取其绝对值		if (hash < 0)			hash = Math.abs(hash);		return hash;		//return Math.abs(string.hashCode());	}}

public class MathUtils {	// 求平均数	public static Double averageValue(Integer[] data) {		Double sum = 0.0;		for (Integer d:data) {			sum += d;		}		return sum/data.length;	}
	// 求标准差	public static Double standardVariance(Integer[] data) {		Double avg = MathUtils.averageValue(data);		Double var = 0.0;		for (Integer d:data) {			// 当前数与平均数的差的平方			var += ((d-avg)*(d-avg));		}
		return Math.sqrt((var/data.length));	}}

public class ConsistentHashTest {
	@Test	public void getNode() {		List<String> nodes = Arrays.asList(			"192.168.0.1",			"192.168.0.2",			"192.168.0.3",			"192.168.0.4",			"192.168.0.5",			"192.168.0.6",			"192.168.0.7",			"192.168.0.8",			"192.168.0.9",			"192.168.0.10"		);		ConsistentHash consistentHash = new ConsistentHash(nodes, 250);
		Map<String, Integer> stat = new HashMap<>();
		for (int i=0; i<1000000; i++) {			String randomString = generateRandomString();			String node = consistentHash.getNode(randomString);			stat.put(node, stat.getOrDefault(node, 0)+1);		}		for (String node:nodes) {			System.out.println("node: "+node+"; count: "+ stat.get(node));		}
		Integer[] data = stat.values().toArray(new Integer[0]);		Double standardVariance = MathUtils.standardVariance(data);		System.out.println("sdv => "+standardVariance);	}
	private String generateRandomString() {		return UUID.randomUUID().toString();	}}