Check if a table column can have a null value or not in Java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;
//from  w  w w .  jav a2 s .c om
public class Main {
  public static void main(String[] args) throws Exception {
    Connection connection = getConnection();

    Statement statement = connection.createStatement();
    ResultSet resultSet = statement.executeQuery("SELECT id, username FROM users");
    ResultSetMetaData metadata = resultSet.getMetaData();
    int nullability = metadata.isNullable(1);

    if (nullability == ResultSetMetaData.columnNullable) {
      System.out.println("Columns ID can have a null value");
    } else if (nullability == ResultSetMetaData.columnNoNulls) {
      System.out.println("Columns ID does not allowed to have a null value");
    } else if (nullability == ResultSetMetaData.columnNullableUnknown) {
      System.out.println("Nullability unknown");
    }
  }

  private static Connection getConnection() throws Exception {
    Class.forName("org.hsqldb.jdbcDriver");
    String url = "jdbc:hsqldb:mem:data/tutorial";

    return DriverManager.getConnection(url, "sa", "");
  }
}