I want to get the set value using DTO
Look at the comments in //.

java.sql.SQLIntegrityConstraintViolationException: Column 'user_id' cannot be null
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException (SQLError.java:117)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException (SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException (SQLExceptionsMapping.java:122)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal (ClientPreparedStatement.java:955)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal (ClientPreparedStatement.java:1094)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal (ClientPreparedStatement.java:1042)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeLargeUpdate (ClientPreparedStatement.java:1345)
    at com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdate (ClientPreparedStatement.java:1027)
    at DB.DAO.regAttendance (DAO.java:180)
    at login.AttendanceInfomation.doPost (AttendanceInfomation.java:60)
    at javax.servlet.http.HttpServlet.service (HttpServlet.java:648)
    at javax.servlet.http.HttpServlet.service (HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter (ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter (ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter (WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter (ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter (ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke (StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke (StandardContextValve.java:94)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke (AuthenticatorBase.java:504)
    at org.apache.catalina.core.StandardHostValve.invoke (StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke (ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke (AbstractAccessLogValve.java:620)
    at org.apache.catalina.core.StandardEngineValve.invoke (StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service (CoyoteAdapter.java:502)
    at org.apache.coyote.http11.AbstractHttp11Processor.process (AbstractHttp11Processor.java:1132)
    at org.apache.coyote.AbstractProtocol $AbstractConnectionHandler.process (AbstractProtocol.java:684)

/**
 * Servlet implementation class AttendanceInfomation
 * /
@WebServlet ("/ AttendanceInfo")
public class AttendanceInfomation extends HttpServlet {
    private static final long serialVersionUID = 1L;
    / **
     * @see HttpServlet # HttpServlet ()
     * /
    public AttendanceInfomation () {
        super ();
        // TODO Auto-generated constructor stub
    }
    / **
     * @see HttpServlet # doGet (HttpServletRequest request, HttpServletResponse
     * response)
     * /
    protected void doGet (HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {// TODO Auto-generated method stub
        response.getWriter (). append ("Served at:") .append (request.getContextPath ());
    }
    / **
     * @see HttpServlet # doPost (HttpServletRequest request, HttpServletResponse
     * response)
     * /
    protected void doPost (HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        DAO dao = new DAO ();
        DTO dto = new DTO ();
        dao.regAttendance (dto.getUserid ());
    }
}

public class DAO {
Private static Connection getConnection () {
Final String DSN = "*";//
Final string USER = "*";
Final string PASSWORD = "*";
Try try {
, Class.forName ("com.mysql.cj.jdbc.Driver");
             return DriverManager.getConnection (DSN, USER, PASSWORD);
} Catch (Exception e) {
             throw new IllegalArgumentException (e);
}
}
Private static void allClose (PreparedStatement statement, Connection connection) {
, If (statement! = Null) {
, Try try {
                        statement.close ();
, C} catch (SQLException e) {
                        e.printStackTrace ();
...}
\}
                if (connection! = null) {
                    try {
                        connection.close ();
                    } catch (SQLException e) {
                        e.printStackTrace ();
                    }
                }
            }
         static Connection connection = null;
            static PreparedStatement statement = null;

public DTO loginUser (String id, String password) {
    DTO dto = new DTO ();
    try {
        connection = getConnection ();
Statement = connection.prepareStatement ("SELECT * FROM login WHERE id =? And password =?");
Statement.setString (1, id);Statement.setString (2, password);
ResultSet resultSet = statement.executeQuery ();
    if (! resultSet.next ()) {
             return null;
}
Else {
              // I want to get this set value with regAttendance
Dto.setUserid (id);
}
}} Catch (SQLException e) {
    E.printStackTrace ();
} Finally {
, AllClose (statement, connection);
}
    return dto;
}
public int regAttendance (String id) {
Int result = 0;
Try try {
Connection = getConnection ();
Statement = connection.prepareStatement ("INSERT INTO time_card (user_id, date, attendance_time) VALUES (?, Now (), now ())");
Statement.setString (1, id);
Result = statement.executeUpdate ();
}} Catch (SQLException e) {
E.printStackTrace ();
} Finally {
, AllClose (statement, connection);
}
        return result;

public class DTO {
    private String userid;
    private String password;
    public String getUserid () {
        return userid;
    }
    public String getPassword () {
        return password;
    }

    public void setUserid (String userid) {
        this.userid = userid;
    }
    public void setPassword (String password) {
        this.password = password;
    }
}

A DTO instance was created in the DAO global variable and set there.

Eclipse