public static boolean checkUser(String id) throws SQLException, NamingException
	{
		boolean check = false;
		
		PreparedStatement stmt = null;
		ResultSet rs = null;		
		
		DataSource ds = getDataSource();
		
    	try 
    	{
			conn = ds.getConnection();			
			
			stmt = conn.prepareStatement(
					"SELECT id FROM users " +
					"WHERE id=?"
					);
			stmt.setString(1,  id);
			rs = stmt.executeQuery();
			
			while(rs.next()) 
			{
				check = true;
			}
		}
    	finally 
		{
			if (rs != null) try{rs.close();} catch(SQLException e) {}
			if (stmt != null) try{stmt.close();} catch(SQLException e) {}
			if (conn != null) try{conn.close();} catch(SQLException e) {}
		}
    	return check;
	}