Inserting Resultset into Arraylist and displaying them

Question

I have difficult storing multiple result sets into an ArrayList. Also I need to display them in a JTextArea. But the problem is, I can't get it to display anything.

public static ArrayList<Wall> getWallPosts(int postId){

    ArrayList<Wall> postList = new ArrayList<Wall>();
    ResultSet rs = null;
    DBController db = new DBController();

    db.setUp("myDatabase");
    String dbQuery = "SELECT Id FROM Wall WHERE ID ="+postId; 

    rs = db.readRequest(dbQuery);

    try{
       while (rs.next()){
            int wallId = rs.getInt("Id");
            String wallPoster = rs.getString("Poster");
            String wallPost = rs.getString("Post");
            String wallDate = rs.getString("Tdate");
            Wall w1 = new Wall(wallPoster, wallPost , wallDate);
            postList.add(w1);   
       }
    }
    catch (Exception e) {
       e.printStackTrace();
    }


    db.terminate();
    return postList;

}
    //The method for displaying the result sets
        public void retrieveCategoryQuestionList() {
    //get the list and store in array
    ArrayList<Wall> aList = Wall.getWallPosts(id);
    for(id = 1; id<aList.size();id++)
        jTextAreaWall.append(w2.getPost());
}

The fields in the database is Id, Poster, Post, Tdate

For future reference, bear in mind that your question doesn't exactly say what is wrong - you just say "I can't get it to display anything", and post a chunk of code. (This is particularly bad because in this situation you must have been getting an exception, so listing that and the stacktrace would have helped a lot). Further reading. — Andrzej Doyle
– Andrzej Doyle, Commented Jan 21, 2011 at 16:22
Ok, the problem is when I run the method below, it just runs DB Query: SELECT * FROM Wall WHERE ID =0. I have changed the codes according to what they said. — Guo Xiuhao
– Guo Xiuhao, Commented Jan 21, 2011 at 16:48

BalusC · Accepted Answer · 2011-01-21 16:54:56Z

5

Here's your SQL query:

"SELECT Id FROM Wall WHERE ID ="+postId

You're selecting only the Id from the table while you expect Id, Poster, Post and Tdate to be present as per your ResultSet#getString() calls.

String wallPoster = rs.getString("Poster");
String wallPost = rs.getString("Post");
String wallDate = rs.getString("Tdate");
Wall w1 = new Wall(wallPoster, wallPost , wallDate);

You need to specify those columns in your SQL query as well:

"SELECT Id, Poster, Post, Tdate FROM Wall WHERE Id="+ postId

2 Comments

Andrzej Doyle Over a year ago

Also, the exception "handling" via e.printStackTrace(); is really bad and will obscure any problems such as this on. DB-accessing methods should always have an unambiguous way of signalling failure (ideally propagating some exception unless used in a very limited scope)!

BalusC Over a year ago

@Andrzej: agreed. And then I'm not talking about the not closing of resources in finally. To the OP: you may find this article useful then to get new insights.

Diana · Accepted Answer · 2012-07-27 20:26:01Z

0

I don't know about other errors that could be, it looks ok to me, just that

String dbQuery = "SELECT Id FROM Wall WHERE ID ="+postId;

Should be:

String dbQuery = "SELECT Id FROM Wall WHERE ID ='"+postId+"'";

answered Jul 27, 2012 at 20:26

Diana

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