Jsp sql update query - mysql

Question

<%
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/questionaire", "root", "root");
Statement st=con.createStatement();
ResultSet rs=st.executeQuery("Select * from question");
List arrlist = new ArrayList();
while(rs.next()){
String xa =rs.getString("display");
if(xa.equals("1")){
arrlist.add(rs.getString("q"));
}
}
Collections.shuffle(arrlist); %>
<%for(int i=0;i<5;i++){
String str = (String) arrlist.get(i);%>
<%=str%> //1
<%st.executeUpdate("update question set display='0' where id=?");%> //comment 2
<br>
<%}%>
This is my code.I have some questions which are displayed,then I shuffle them and randomly select 5 questions.The 5 randomly selected questions need to be given display='0' as can be seen in comment 2.How do I do it.I need to pass the id that str has to the database.Could anyone help?

Answer 1

1.) When selecting your questions you should not only "remember" the question-text but also the id. Why not create a new "Question"-class that can keep both values and possibly some more information(correct answer etc.).
public class Question {
private int id;
private String questionText;
private String answer;
private boolean display=false;
public Question(int id,String questionText,String answer) {
this.id = id;
this.questionText = questionText;
this.answer= answer;
}
public int getId() {
return id;
}
public String getQuestionText() {
return questionText;
}
public String getAnswer() {
return answer;
}
public boolean getDisplay() {
return display;
}
public void setDisplay(boolean display) {
this.display = display;
}
}
For each entry in your result-set create a new Question-object and add it to your question-list.
2.) You can't use the =?-syntax with a plain jdbc-Statement-object. You will have to use PreparedStatement for this, then you can set your query-parameters via the setXXX()-methods:
PreparedStatement stmt = conn.prepareStatement("update question set display='0' where id=?");
stmt.setInt(1, question.getId());
stmt.executeUpdate();
3.) When multiple users access your application I'm pretty sure you will get in trouble keeping your "display-state" in the database. Instead use the display-property of the Question-object (see above).