track the cache hit rate

pdb-utils/src/main/java/org/lucares/utils/cache/LRUCache.java

@@ -6,6 +6,9 @@ import java.util.Map;
 public class LRUCache<K, V> {
     private final LinkedHashMap<K, V> cache;
 
+    private long countGet = 0;
+    private long countGetHits = 0;
+
     public LRUCache(final int maxEntries) {
         this.cache = new LinkedHashMap<>(16, 0.75f, true) {
             private static final long serialVersionUID = 1L;
@@ -21,7 +24,12 @@ public class LRUCache<K, V> {
     }
 
     public V get(final K key) {
-        return cache.get(key);
+        final V result = cache.get(key);
+        countGet++;
+        if (result != null) {
+            countGetHits++;
+        }
+        return result;
     }
 
     public V remove(final K key) {
@@ -32,4 +40,7 @@ public class LRUCache<K, V> {
         return cache.size();
     }
 
+    public double cacheHitRate() {
+        return (double) countGetHits / (double) countGet;
+    }
 }