如何从JAVA httpSession获取参数并在dao类上使用/设置它？

Question

I need to use a servlet to validate login/password. That's fine already.

I have a method in a DAO class that returns a resultSet list of values through a prepareStatement.

I'm using a query that brings this filtered result with a where clause (by user's name).

The problem is: how can I get the servlet parameter (name of the user who logged in) and set it on the prepareStatement ?

The code follows:

public class DaoPojoJoin extends Dao {

public List<PojoJoin> listUserDegrees() {
    List<PojoJoin> dg = new ArrayList<PojoJoin>();
    if (openConnection()) {
        try {
            st = cn.prepareStatement("SELECT USER, MATTER, DEGREE FROM DEGREES x "
                    + "right outer join USERS y on x.idUser=y.idUser "
                    + "right outer join MATTER z on idMatter=z.idMatter "
                    + "where x.iduser=?"); // filter result by user's name

            // How can I have something like this:
            // st.setString(1,usr.request.getParameter("user"));

            // or this:
            // st.setString(1,.getAttribute(user));

            rs = st.executeQuery();
            while (rs.next()) {
                PojoJoin pj = new PojoJoin();
                rs.getString("USER"); 
                rs.getString("MATTER");
                rs.getDouble("DEGREE");
                pj.setUsuario(rs.getString("USER"));
                pj.setDisciplina(rs.getString("MATTER"));
                pj.setNota(rs.getDouble("DEGREE"));
                nota.add(pj);
            }
        } catch (Exception ex) {
            err = ex.getMessage();
        } finally {
            closeConnection();
        }
    }
    return dg;
}

}

Thanks in advance.

Answer 1

Ask for it as method argument. The DAO should not care about the context it is sitting in and is supposed to be reuseable everywhere else (eg a plain vanilla Java Application which doesn't use servlets).

Thus so

public List<PojoJoin> listUserDegrees(String username) {
    // ...
}

or

public List<PojoJoin> listUserDegrees(Long userId) {
    // ...
}

or

public List<PojoJoin> listUserDegrees(User user) {
    // ...
}

Finally just let the caller (the servlet) pass it in.

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Unrelated to the concrete problem, your DB resource handling doesn't seem to be threadsafe. I'd work on that to avoid serious problems whenever your webapp starts to be used by multiple users.