分层实验的示例代码。原文见这里：http://blog.sina.com.cn/s/blog_e59371cc0102vopg.html ，但是其中代码格式错乱了，帮忙整理了一下。

MultiLayerExperiment.java

// Overlapping Experiment Demo
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.LinkedList;
import java.util.List;

public class MultiLayerExperiment {
    private static String byteArrayToHex(byte[] byteArray) {
        char[] hexDigits = {'0', '1', '2', '3', '4', '5', '6', '7',
                '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
        char[] resultCharArray = new char[byteArray.length * 2];
        int index = 0;
        for (byte b : byteArray) {
            resultCharArray[index++] = hexDigits[b >>> 4 & 0xf];
            resultCharArray[index++] = hexDigits[b & 0xf];
        }
        return new String(resultCharArray);
    }

    private static long splitBucket(MessageDigest md5, long val, String shuffle){
        String key = String.valueOf(val) +((shuffle==null)?"":shuffle);
        byte[] ret = md5.digest(key.getBytes());
        String s = byteArrayToHex(ret) ;
        long hash =Long.parseLong(s.substring(s.length() - 16, s.length() - 1), 16);
        if(hash < 0){
            hash = hash * (-1);
        }
        return hash ;
    }

    private static void exp(SecureRandom sr,MessageDigest md5,
                            final int LevelOneBucketNumm,
                            final int LevelTwoBucketNumm,
                            final int LevelThreeBucketNumm,
                            final int AllFlows,
                            String shuffleLevel1,
                            String shuffleLevel2,
                            String shuffleLevel3){
        // 1st layer
        System.out.println("==第1层实验 start!==");
        int[] bucketlevel1 = new int[LevelOneBucketNumm];
        for (int i=0; i<LevelOneBucketNumm; ++i) {
            bucketlevel1[i] = 0;
        }
        List<Integer> level1bucket2 = new LinkedList<Integer>();
        for(int i=0; i<AllFlows; ++i){
            int cookie = sr.nextInt();
            long hashValue = splitBucket(md5, cookie, shuffleLevel1);
            int bucket =(int) (hashValue % LevelOneBucketNumm);
            if(bucket == 2){
                level1bucket2.add(cookie);
            }
            bucketlevel1[bucket]++;
        }
        for(int i=0; i<LevelOneBucketNumm; ++i){
            System.out.println("1层" + i + "桶:" + bucketlevel1[i]);
        }
        System.out.println("==第1层实验 end!==");
        // 2nd layer
        System.out.println("==第1层2号桶流量到达第2层实验 start!==");
        int[] bucketlevel2 = new int[LevelTwoBucketNumm];
        for (int i=0; i<LevelTwoBucketNumm; ++i) {
            bucketlevel2[i] = 0;
        }
        List<Integer> level2bucket2 = new LinkedList<Integer>();
        for(int cookie : level1bucket2) {
            long hashValue = splitBucket(md5, cookie, shuffleLevel2);
            int bucket =(int) (hashValue % LevelTwoBucketNumm);
            if(bucket == 2){
                level2bucket2.add(cookie);
            }
            bucketlevel2[bucket]++;
        }
        for(int i=0; i<LevelTwoBucketNumm; ++i) {
            System.out.println("2层" + i + "桶:" + bucketlevel2[i]);
        }
        System.out.println("==第1层2号桶流量到达第2层实验 end!==");
        // 3rd layer
        System.out.println("==第2层2号桶流量到达第3层实验 start!==");
        int[] bucketlevel3 = new int[LevelThreeBucketNumm];
        for (int i=0; i<LevelThreeBucketNumm; ++i) {
            bucketlevel3[i] = 0;
        }
        for(int cookie : level2bucket2) {
            long hashValue = splitBucket(md5, cookie, shuffleLevel3);
            int bucket =(int) (hashValue % LevelThreeBucketNumm);

            bucketlevel3[bucket]++;
        }
        for(int i=0; i<LevelThreeBucketNumm; ++i) {
            System.out.println("3层" + i + "桶:" + bucketlevel3[i]);
        }
        System.out.println("==第2层2号桶流量到达第3层实验 end!==");
    }

    public static void main(String[] args) throws NoSuchAlgorithmException {
        SecureRandom sr =  SecureRandom.getInstance("SHA1PRNG");
        MessageDigest md5 =  MessageDigest.getInstance("MD5");

        exp(sr,md5,5,5,5,1000000,null,null,null);
        System.out.println("=======================");
        exp(sr,md5,5,5,5,1000000,"a","b","c");
    }
}