选择特定的组合框项目时，将空值插入数据库

Question

当我选择一个特定的组合框项目时，我想在数据库中输入空值，这样我就可以获得该列的rowcount而留下空行

String bnn = (txtboxno.getText().trim() == null || 
              txtboxno.getText().equals("")) ? "null" : txtboxno.getText();
Object nsn = (cbnotstat.getSelectedItem() == null || cbnotstat.getSelectedItem().equals("")) ? "0" : cbnotstat.getSelectedItem();

PreparedStatement stmt = con.prepareStatement("select COUNT(box_no)as total from soil_det WHERE rm_id = ?");
ResultSet rs;
String rm = tf_rm_id.getText();
stmt.setLong(1, Long.parseLong(rm));
rs = stmt.executeQuery();

while (rs.next()) {
    tf_boxno.setText(rs.getString("total"));
}

我上面已经尝试过，但它显示的是inputtring“null”错误。

Answer 1

同样你需要检查rm_id

String rm = tf_rm_id.getText();
rm = rm == null || rm.isEmpty() ? 0 : rm ; // consider 0 is valid here
long value ;
try {
  value = Long.parseLong(rm) ;
  stmt.setLong(1, value);
} catch(NumberFormatException  ee) {
  System.out.println("Praser exception, invalid input");
}