Reading all rows from database and putting them into ArrayList - Java

Question

I've the below code,

ArrayList<ArrayList<String>> outer = new ArrayList<ArrayList<String>>();
ArrayList<String> inner = new ArrayList<String>(); 
ResultSet rs = statement.executeQuery(sqlQuery);
ResultSetMetaData rsmd = rs.getMetaData();
int columnsNumber = rsmd.getColumnCount();
while (rs.next()) {
    for(int i=1; i<=columnsNumber; i++){
        inner.add(rs.getString(i));
    }                   
}
outer.add(inner);
return outer;

What I get for outer is something like this

[[100, 200, 300, 100, 200, 300]]

What I'm trying to get is

[[100, 200, 300], [100, 200, 300]]

I want each row to be an unique item in the list, but what I get is a list of all rows in one item in the list.

How do I do it?

Can someone help me out?

uraimo · Accepted Answer · 2015-03-18 13:46:40Z

3

Create a new inner for each record and add it to outer.

ArrayList<String> inner; 
ResultSet rs = statement.executeQuery(sqlQuery);
ResultSetMetaData rsmd = rs.getMetaData();

while (rs.next()) {
    inner = new ArrayList<String>(); 
    for(int i=1; i<=columnsNumber; i++){
       inner.add(rs.getString(i));
    }    
    outer.add(inner);               
}

answered Mar 18, 2015 at 13:46

uraimo

20k8 gold badges50 silver badges57 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

bademba Over a year ago

You are a genious. It helped me buddy

Konstantin Yovkov · Accepted Answer · 2015-03-18 13:46:18Z

2

On each step of the while loop, you have to re-initialize the inner list with an empty one and and add it to the outer list before the step has finished:

while (rs.next()) {
    inner = new ArrayList<String>();
    for(int i=1; i<=columnsNumber; i++){
        inner.add(rs.getString(i));
    }                   
    outer.add(inner);
}

answered Mar 18, 2015 at 13:46

Konstantin Yovkov

63k9 gold badges107 silver badges152 bronze badges

Comments

Anderson Vieira · Accepted Answer · 2015-03-18 14:05:15Z

1

Since outer is a list of lists, in each iteration of the while loop you will need to:

Reinitialize the inner list
Fill the inner list
Store this version of the inner list in the outer list.

I would also keep the inner declaration inside the while loop to limit its scope, like this:

List<List<String>> outer = new ArrayList<>();
ResultSet rs = statement.executeQuery(sqlQuery);
ResultSetMetaData rsmd = rs.getMetaData();
int columnsNumber = rsmd.getColumnCount();
while (rs.next()) {
    List<String> inner = new ArrayList<>(); 
    for(int i = 1; i <= columnsNumber; i++) {
       inner.add(rs.getString(i));
    }    
    outer.add(inner);               
}
return outer;

edited Mar 18, 2015 at 14:05

answered Mar 18, 2015 at 13:52

Anderson Vieira

9,0692 gold badges40 silver badges48 bronze badges

Collectives™ on Stack Overflow

Reading all rows from database and putting them into ArrayList - Java

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related