bug fixed for sql stat maxSize

src/main/java/com/alibaba/druid/util/LRUCache.java

@@ -0,0 +1,19 @@
+package com.alibaba.druid.util;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+public class LRUCache<K, V> extends LinkedHashMap<K, V> {
+
+    private static final long serialVersionUID = 1L;
+    private final int         maxSize;
+
+    public LRUCache(int maxSize, int initialCapacity, float loadFactor, boolean accessOrder){
+        super(initialCapacity, loadFactor, accessOrder);
+        this.maxSize = maxSize;
+    }
+    
+    protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
+        return this.size() > this.maxSize;
+    }
+}