public List <User> search_user(MapPoint center, int r){
		try{
			log.debug("search_user is invoked");
			Statement statement = getStatement();
			ResultSet res = statement.executeQuery("select * from user");
			List <User> res_users = new ArrayList<User>();
			int i = 0;
			while(res.next()){
				log.debug("res has " + i++);
				res_users.add(new User(res.getInt("uid"), res.getString("username"), 
						res.getString("password"), res.getInt("motion"),
						res.getInt("motoinLevel"), res.getString("signature"),
						res.getInt("sex"), res.getInt("lat"), res.getInt("lon"),
						res.getInt("state")));
			}
			return res_users;
		}
		catch(SQLException E){
			E.printStackTrace();
		}
		return null;
		/*
		PreparedStatement statement = null;
		try{
			statement =  getPreparedStatement(SearchPerson);
			statement.setInt(1, center.lat);
			statement.setInt(2, center.lat);
			statement.setInt(3, center.lon);
			statement.setInt(4, center.lon);
			statement.setInt(5, r);
			statement.setInt(6, r);
			ResultSet res = statement.executeQuery();
			List <User> res_users = new ArrayList<User>();
			while(res.next()){
				res_users.add(new User(res.getInt("uid"), res.getString("username"), 
						res.getString("password"), res.getInt("motion"),
						res.getInt("motoinLevel"), res.getString("signature"),
						res.getInt("sex"), res.getInt("lat"), res.getInt("lon"),
						res.getInt("state")));
			}
			return res_users;
		}
		catch(SQLException E){
			E.printStackTrace();
		}finally {
			try {
				Connection conn = statement.getConnection();
				statement.close();
				conn.close();
			} catch (SQLException e) {
				e.printStackTrace();
				log.error("Exception : close statement or connection error! in insert_server");
			}
		}
		return null;
		*/
	}