Statement.getGeneratedKeys（）方法

Question

I'm currently watching a video tutorial, and I am really confused with this code:

public static boolean insert(Member mbr) throws Exception {

    String SQL = "INSERT INTO test (first_name, last_name) " +
                "VALUES (?, ?)";
    ResultSet keys = null;
    try (
            Connection con = DBUtil.getConnection(DBType.MYSQL);
            PreparedStatement stmt = con.prepareStatement(SQL, Statement.RETURN_GENERATED_KEYS);
        ) {

        stmt.setString(1, mbr.getFname());
        stmt.setString(2,  mbr.getLname());
        int affected = stmt.executeUpdate();

        if (affected == 1) {
            keys = stmt.getGeneratedKeys();
            keys.next();
            int newKey = keys.getInt(1);
            mbr.setMemberid(newKey);
        } else {
            System.err.println("No rows affected");
            return false;
        } 
    } finally {
        if (keys != null) keys.close();
    }
    return true;
}

Regarding the stmt.getGeneratedKeys() method, since it returns the auto-generated key as a result of executing the Statement object, why does it need to invoke the getInt() method?

Also, the cursor, by default, is pointing before the inserted row so why is the next() method invoked before the get.GeneratedKeys() ? Shouldn't the next() method be invoked first so that the cursor will go to the first result row before getting the GeneratedKey ?

Answer 1

Two things. Some databases can return multiple generated keys per row, and they do not have to be integers, they could be a GUID string or something else. Therefore, you need to call getInt(1) in the code above. Second, you are incorrect, a ResultSet returned by JDBC is positioned before the first row, thus the need to call next(). If a ResultSet has no rows, calling next() returns false indicating there are no results.