support clearStatementCache

src/main/java/com/alibaba/druid/pool/PreparedStatementPool.java

@@ -17,6 +17,7 @@ package com.alibaba.druid.pool;
 
 import java.sql.PreparedStatement;
 import java.sql.SQLException;
+import java.util.Iterator;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -74,6 +75,19 @@ public class PreparedStatementPool {
             }
         }
     }
+    
+    public void clear() {
+        Iterator<Entry<PreparedStatementKey, PreparedStatementHolder>> iter = map.entrySet().iterator();
+        while (iter.hasNext()) {
+            Entry<PreparedStatementKey, PreparedStatementHolder> entry = iter.next();
+            
+            dataSource.closePreapredStatement(entry.getValue());
+            dataSource.decrementCachedPreparedStatementCount();
+            dataSource.incrementCachedPreparedStatementDeleteCount();
+            
+            iter.remove();
+        }
+    }
 
     public Map<PreparedStatementKey, PreparedStatementHolder> getMap() {
         return map;