采样算法

import java.security.SecureRandom;
import java.util.BitSet;
import java.util.Random;
import java.util.concurrent.atomic.AtomicInteger;

public class RequestSampler {

 private final AtomicInteger counter = new AtomicInteger(0);
 private final BitSet sampleDecisions;
 private float percentage =0.1f;
 private static float percentCount = 10000.0f;

 public RequestSampler(float percentage) {
  RequestSampler.setPercentCount(1/percentage);
  int outOf100 = (int) (percentage * percentCount);
  this.sampleDecisions = randomBitSet((int)percentCount, outOf100, new SecureRandom());
  this.percentage = percentage;
 }

 public boolean isSampled() {
  if (this.percentage == 0) {
   return false;
  } else if (this.percentage == percentCount) {
   return true;
  }
  synchronized (this) {
   final int i = this.counter.getAndIncrement();
   boolean result = this.sampleDecisions.get(i);
   if (i == (percentCount-1)) {
    this.counter.set(0);
   }
   return result;
  }
 }

 private BitSet randomBitSet(int size, int cardinality, Random rnd) {
  BitSet result = new BitSet(size);
  int[] chosen = new int[cardinality];
  int i;
  for (i = 0; i < cardinality; ++i) {
   chosen[i] = i;
   result.set(i);
  }
  for (; i < size; ++i) {
   int j = rnd.nextInt(i + 1);
   if (j < cardinality) {
    result.clear(chosen[j]);
    result.set(i);
    chosen[j] = i;
   }
  }
  return result;
 }

 public static float getPercentCount() {
  return percentCount;
 }

 public static void setPercentCount(float percentCount) {
  RequestSampler.percentCount = percentCount;
 }
 
}