Add rate limiting code

implementations/java/rate_limiting/TokenBucket.java

@@ -0,0 +1,36 @@
+package implementations.java.rate_limiting;
+
+import java.time.Instant;
+
+public class TokenBucket {
+    private final long capacity;        // Maximum number of tokens the bucket can hold
+    private final double fillRate;      // Rate at which tokens are added to the bucket (tokens per second)
+    private double tokens;              // Current number of tokens in the bucket
+    private Instant lastRefillTimestamp; // Last time we refilled the bucket
+
+    public TokenBucket(long capacity, double fillRate) {
+        this.capacity = capacity;
+        this.fillRate = fillRate;
+        this.tokens = capacity;  // Start with a full bucket
+        this.lastRefillTimestamp = Instant.now();
+    }
+
+    public synchronized boolean allowRequest(int tokens) {
+        refill();  // First, add any new tokens based on elapsed time
+
+        if (this.tokens < tokens) {
+            return false;  // Not enough tokens, deny the request
+        }
+
+        this.tokens -= tokens;  // Consume the tokens
+        return true;  // Allow the request
+    }
+
+    private void refill() {
+        Instant now = Instant.now();
+        // Calculate how many tokens to add based on the time elapsed
+        double tokensToAdd = (now.toEpochMilli() - lastRefillTimestamp.toEpochMilli()) * fillRate / 1000.0;
+        this.tokens = Math.min(capacity, this.tokens + tokensToAdd);  // Add tokens, but don't exceed capacity
+        this.lastRefillTimestamp = now;
+    }
+}