滑动窗口计数java实现

滑动窗口计数有很多使用场景，比如说限流防止系统雪崩。相比计数实现，滑动窗口实现会更加平滑，能自动消除毛刺。

概念上可以参考TCP的滑窗算法，可以看一下这篇文章（http://go12345.iteye.com/blog/1744728）。在实现上，滑动窗口算法需要循环队列和线程安全保障。

下面的实现有几个点

1， 支持滑窗大小运行时动态调整

2， 基于 java8 编译器

3， DEMO实现只支持一个窗口对象，如果要支持多个，需要修改 SlotBaseCounter 类

1. package slidingwindow;
2. import java.util.Arrays;
3. import java.util.concurrent.atomic.AtomicInteger;
4. /**
5. * Created by admin on 2016/02/20.
6. */
7. public class SlotBaseCounter {
8. private int slotSize;
9. private AtomicInteger[] slotCounter;
10. public SlotBaseCounter(int slotSize) {
11. slotSize = slotSize < 1 ? 1 : slotSize;
12. this.slotSize = slotSize;
13. this.slotCounter = new AtomicInteger[slotSize];
14. for (int i = 0; i < this.slotSize; i++) {
15. slotCounter[i] = new AtomicInteger(0);
16. }
17. }
18. public void increaseSlot(int slotSize) {
19. slotCounter[slotSize].incrementAndGet();
20. }
21. public void wipeSlot(int slotSize) {
22. slotCounter[slotSize].set(0);
23. }
24. public int totalCount() {
25. return Arrays.stream(slotCounter).mapToInt(slotCounter -> slotCounter.get()).sum();
26. }
27. @Override
28. public String toString() {
29. return Arrays.toString(slotCounter);
30. }
31. }

1. package slidingwindow;
2. /**
3. * Created by admin on 2016/02/20.
4. */
5. public class SlidingWindowCounter {
6. private volatile SlotBaseCounter slotBaseCounter;
7. private volatile int windowSize;
8. private volatile int head;
9. public SlidingWindowCounter(int windowSize) {
10. resizeWindow(windowSize);
11. }
12. public synchronized void resizeWindow(int windowSize) {
13. this.windowSize = windowSize;
14. this.slotBaseCounter = new SlotBaseCounter(windowSize);
15. this.head = 0;
16. }
17. public void increase() {
18. slotBaseCounter.increaseSlot(head);
19. }
20. public int totalAndAdvance() {
21. int total = totalCount();
22. advance();
23. return total;
24. }
25. public void advance() {
26. int tail = (head + 1) % windowSize;
27. slotBaseCounter.wipeSlot(tail);
28. head = tail;
29. }
30. public int totalCount() {
31. return slotBaseCounter.totalCount();
32. }
33. @Override
34. public String toString() {
35. return "total = " + totalCount() + " head = " + head + " >> " + slotBaseCounter;
36. }
37. }

1. package slidingwindow;
2. import java.util.concurrent.TimeUnit;
3. /**
4. * Created by admin on 2016/02/20.
5. */
6. public class Loops {
7. public static void dieLoop(Runnable runnable) {
8. while (true) {
9. run(runnable);
10. }
11. }
12. public static void rateLoop(Runnable runnable, int mills) {
13. while (true) {
14. try {
15. TimeUnit.MILLISECONDS.sleep(mills);
16. } catch (InterruptedException e) {
17. }
18. run(runnable);
19. }
20. }
21. public static void fixLoop(Runnable runnable, int loop) {
22. for (int i = 0; i < loop; i++) {
23. run(runnable);
24. }
25. }
26. private static void run(Runnable runnable) {
27. try {
28. runnable.run();
29. } catch (Exception e) {
30. e.printStackTrace();
31. }
32. }
33. }

1. package slidingwindow;
2. import org.junit.Test;
3. import java.io.IOException;
4. import java.util.Random;
5. import java.util.Scanner;
6. import java.util.concurrent.ExecutorService;
7. import java.util.concurrent.Executors;
8. import java.util.concurrent.ScheduledExecutorService;
9. import java.util.concurrent.TimeUnit;
10. /**
11. * Created by admin on 2016/02/20.
12. */
13. public class SlidingWindowCounterTest {
14. private ExecutorService es = Executors.newCachedThreadPool();
15. private ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor();
16. @Test
17. public void testNWindow() throws IOException {
18. SlidingWindowCounter swc = new SlidingWindowCounter(3);
19. ses.scheduleAtFixedRate(() -> {
20. Loops.fixLoop(swc::increase, new Random().nextInt(10));
21. }, 10, 2, TimeUnit.MILLISECONDS);
22. ses.scheduleAtFixedRate(() -> {
23. System.out.println(swc);
24. swc.advance();
25. }, 1, 1, TimeUnit.SECONDS);
26. ses.scheduleAtFixedRate(() -> {
27. swc.resizeWindow(new Random().nextInt(10));
28. }, 1, 10, TimeUnit.SECONDS);
29. System.in.read();
30. }
31. @Test
32. public void test1Window() {
33. SlidingWindowCounter swc = new SlidingWindowCounter(1);
34. System.out.println(swc);
35. swc.increase();
36. swc.increase();
37. System.out.println(swc);
38. swc.advance();
39. System.out.println(swc);
40. swc.increase();
41. swc.increase();
42. System.out.println(swc);
43. }
44. @Test
45. public void test3Window() {
46. SlidingWindowCounter swc = new SlidingWindowCounter(3);
47. System.out.println(swc);
48. swc.increase();
49. System.out.println(swc);
50. swc.advance();
51. System.out.println(swc);
52. swc.increase();
53. swc.increase();
54. System.out.println(swc);
55. swc.advance();
56. System.out.println(swc);
57. swc.increase();
58. swc.increase();
59. swc.increase();
60. System.out.println(swc);
61. swc.advance();
62. System.out.println(swc);
63. swc.increase();
64. swc.increase();
65. swc.increase();
66. swc.increase();
67. System.out.println(swc);
68. swc.advance();
69. System.out.println(swc);
70. }
71. }

这是部分测试结果输出：

total = 2245 head = 0 >> [2245, 0, 0, 0, 0, 0]

total = 4561 head = 1 >> [2245, 2316, 0, 0, 0, 0]

total = 6840 head = 2 >> [2245, 2316, 2279, 0, 0, 0]

total = 8994 head = 3 >> [2245, 2316, 2279, 2154, 0, 0]

total = 11219 head = 4 >> [2245, 2316, 2279, 2154, 2225, 0]

total = 13508 head = 5 >> [2245, 2316, 2279, 2154, 2225, 2289]

total = 13602 head = 0 >> [2339, 2316, 2279, 2154, 2225, 2289]

total = 13465 head = 1 >> [2339, 2179, 2279, 2154, 2225, 2289]

total = 13474 head = 2 >> [2339, 2179, 2288, 2154, 2225, 2289]

total = 13551 head = 3 >> [2339, 2179, 2288, 2231, 2225, 2289]

total = 2192 head = 0 >> [2192]

total = 2207 head = 0 >> [2207]

total = 2291 head = 0 >> [2291]

total = 2257 head = 0 >> [2257]

total = 2250 head = 0 >> [2250]

total = 2201 head = 0 >> [2201]

total = 2299 head = 0 >> [2299]

total = 2223 head = 0 >> [2223]

total = 2190 head = 0 >> [2190]

total = 2306 head = 0 >> [2306]

total = 2290 head = 0 >> [2290, 0, 0, 0, 0, 0, 0, 0, 0]

total = 4474 head = 1 >> [2290, 2184, 0, 0, 0, 0, 0, 0, 0]

total = 6632 head = 2 >> [2290, 2184, 2158, 0, 0, 0, 0, 0, 0]

total = 8744 head = 3 >> [2290, 2184, 2158, 2112, 0, 0, 0, 0, 0]

total = 11008 head = 4 >> [2290, 2184, 2158, 2112, 2264, 0, 0, 0, 0]

total = 13277 head = 5 >> [2290, 2184, 2158, 2112, 2264, 2269, 0, 0, 0]

total = 15446 head = 6 >> [2290, 2184, 2158, 2112, 2264, 2269, 2169, 0, 0]

total = 17617 head = 7 >> [2290, 2184, 2158, 2112, 2264, 2269, 2169, 2171, 0]

total = 19749 head = 8 >> [2290, 2184, 2158, 2112, 2264, 2269, 2169, 2171, 2132]

total = 19608 head = 0 >> [2149, 2184, 2158, 2112, 2264, 2269, 2169, 2171, 2132]

total = 2256 head = 0 >> [2256, 0, 0, 0]

total = 4624 head = 1 >> [2256, 2368, 0, 0]

total = 6811 head = 2 >> [2256, 2368, 2187, 0]

total = 8973 head = 3 >> [2256, 2368, 2187, 2162]

total = 8934 head = 0 >> [2217, 2368, 2187, 2162]

total = 8798 head = 1 >> [2217, 2232, 2187, 2162]

total = 8912 head = 2 >> [2217, 2232, 2301, 2162]

total = 8940 head = 3 >> [2217, 2232, 2301, 2190]

total = 8987 head = 0 >> [2264, 2232, 2301, 2190]

total = 9049 head = 1 >> [2264, 2294, 2301, 2190]

total = 2220 head = 0 >> [2220, 0, 0, 0, 0, 0, 0]

total = 4477 head = 1 >> [2220, 2257, 0, 0, 0, 0, 0]

total = 6718 head = 2 >> [2220, 2257, 2241, 0, 0, 0, 0]

total = 8939 head = 3 >> [2220, 2257, 2241, 2221, 0, 0, 0]

total = 11174 head = 4 >> [2220, 2257, 2241, 2221, 2235, 0, 0]

total = 13420 head = 5 >> [2220, 2257, 2241, 2221, 2235, 2246, 0]

total = 15673 head = 6 >> [2220, 2257, 2241, 2221, 2235, 2246, 2253]

total = 15779 head = 0 >> [2326, 2257, 2241, 2221, 2235, 2246, 2253]

total = 15796 head = 1 >> [2326, 2274, 2241, 2221, 2235, 2246, 2253]

total = 15802 head = 2 >> [2326, 2274, 2247, 2221, 2235, 2246, 2253]