Add rate limiting code

implementations/java/rate_limiting/SlidingWindowCounter.java

@@ -0,0 +1,42 @@
+package implementations.java.rate_limiting;
+
+import java.time.Instant;
+
+public class SlidingWindowCounter {
+    private final long windowSizeInSeconds;   // Size of the sliding window in seconds
+    private final long maxRequestsPerWindow;  // Maximum number of requests allowed in the window
+    private long currentWindowStart;          // Start time of the current window
+    private long previousWindowCount;         // Number of requests in the previous window
+    private long currentWindowCount;          // Number of requests in the current window
+
+    public SlidingWindowCounter(long windowSizeInSeconds, long maxRequestsPerWindow) {
+        this.windowSizeInSeconds = windowSizeInSeconds;
+        this.maxRequestsPerWindow = maxRequestsPerWindow;
+        this.currentWindowStart = Instant.now().getEpochSecond();
+        this.previousWindowCount = 0;
+        this.currentWindowCount = 0;
+    }
+
+    public synchronized boolean allowRequest() {
+        long now = Instant.now().getEpochSecond();
+        long timePassedInWindow = now - currentWindowStart;
+
+        // Check if we've moved to a new window
+        if (timePassedInWindow >= windowSizeInSeconds) {
+            previousWindowCount = currentWindowCount;
+            currentWindowCount = 0;
+            currentWindowStart = now;
+            timePassedInWindow = 0;
+        }
+
+        // Calculate the weighted count of requests
+        double weightedCount = previousWindowCount * ((windowSizeInSeconds - timePassedInWindow) / (double) windowSizeInSeconds)
+                + currentWindowCount;
+
+        if (weightedCount < maxRequestsPerWindow) {
+            currentWindowCount++;  // Increment the count for this window
+            return true;           // Allow the request
+        }
+        return false;  // We've exceeded the limit, deny the request
+    }    
+}