cache disk blocks in an LRU cache

Improves read access by factor 4 for small trees.

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

@@ -0,0 +1,35 @@
+package org.lucares.utils.cache;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+public class LRUCache<K, V> {
+	private final LinkedHashMap<K, V> cache;
+
+	public LRUCache(final int maxEntries) {
+		this.cache = new LinkedHashMap<>(16, 0.75f, true) {
+			private static final long serialVersionUID = 1L;
+
+			protected boolean removeEldestEntry(final Map.Entry<K, V> eldest) {
+				return size() > maxEntries;
+			}
+		};
+	}
+
+	public V put(final K key, final V value) {
+		return cache.put(key, value);
+	}
+
+	public V get(final K key) {
+		return cache.get(key);
+	}
+
+	public V remove(final K key) {
+		return cache.remove(key);
+	}
+
+	public int size() {
+		return cache.size();
+	}
+
+}