1. import java.util.HashMap;
  2. import java.util.Map;
  3. import java.util.concurrent.ConcurrentHashMap;
  5. public class TokenFilter {
  7. private final Map<String, Integer> tokenUsage; // Token ID -> Usage count
  8. private final int maxUsage; // Maximum allowed usage per token
  9. private final long timeWindowMillis; // Time window for rate limiting
  11. public TokenFilter(int maxUsage, long timeWindowMillis) {
  12. this.tokenUsage = new ConcurrentHashMap<>();
  13. this.maxUsage = maxUsage;
  14. this.timeWindowMillis = timeWindowMillis;
  15. }
  17. /**
  18. * Filters a list of authentication tokens for maintenance tasks based on rate limiting.
  19. * @param tokens A list of authentication tokens.
  20. * @return A list of valid tokens.
  21. */
  22. public Iterable<String> filterTokens(Iterable<String> tokens) {
  23. java.util.List<String> validTokens = new java.util.ArrayList<>();
  24. long currentTime = System.currentTimeMillis();
  26. for (String token : tokens) {
  27. if (isTokenAllowed(token, currentTime)) {
  28. validTokens.add(token);
  29. }
  30. }
  32. return validTokens;
  33. }
  35. private boolean isTokenAllowed(String token, long currentTime) {
  36. // Get the current usage count for the token. If it doesn't exist, it's 0.
  37. int currentUsage = tokenUsage.getOrDefault(token, 0);
  39. // Check if the token usage exceeds the maximum allowed.
  40. if (currentUsage >= maxUsage) {
  41. return false; // Rate limited
  42. }
  44. // Increment the usage count for the token.
  45. tokenUsage.put(token, currentUsage + 1);
  47. // Clean up old usage entries.
  48. cleanupOldUsage(currentTime);
  50. return true; // Token is allowed
  51. }
  54. private void cleanupOldUsage(long currentTime) {
  55. // Remove tokens that haven't been used within the time window.
  56. tokenUsage.entrySet().removeIf(entry -> {
  57. long lastUsageTime = entry.getValue();
  58. return (currentTime - lastUsageTime) > timeWindowMillis;
  59. });
  60. }
  63. public static void main(String[] args) {
  64. //Example Usage
  65. TokenFilter filter = new TokenFilter(3, 60000); // Allow 3 uses per minute
  67. java.util.List<String> tokens = java.util.List.of("token1", "token2", "token1", "token3", "token2", "token1", "token4");
  68. java.util.List<String> validTokens = filter.filterTokens(tokens);
  70. System.out.println("Valid Tokens: " + validTokens);
  71. }
  72. }

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