support spring Jdbc4NativeJdbcExtractor

src/main/java/com/alibaba/druid/proxy/jdbc/ResultSetProxyImpl.java

@@ -1050,4 +1050,12 @@ public class ResultSetProxyImpl extends WrapperProxyImpl implements ResultSetPro
         throw new SQLFeatureNotSupportedException();
     }
 
+    @SuppressWarnings("unchecked")
+    public <T> T unwrap(Class<T> iface) throws SQLException {
+        if (iface == ResultSet.class) {
+            return (T) resultSet;
+        }
+        
+        return super.unwrap(iface);
+    }
 }