将ResultSet转换为int数组

Question

I am trying to convert ResultSet to array of int , that because the method I have returns int[] :

public static int[] GetPathIDsFromDB (String Dbnum, int objectid) throws SQLException{
    String selectSQL = "SELECT ID FROM " + Dbnum + ".tabName where ObjectID=?";
    dbConnection = getDBConnection();
    preparedStatement = dbConnection.prepareStatement(selectSQL);
    preparedStatement.setInt(1 , objectid);
    ResultSet rs = preparedStatement.executeQuery();  
    //int [] rsIDs = new rs.count;
    int [] rsIDs = null;
    while (rs.next()) {
        rsIDs=rs.getInt(1); // the error int cannot be converted to int[]
    }
    return rsIDs;
}

How can I convert that ?

Answer 1

Personally, I would put them into a list, then convert to an array at the end.

List<Integer> rsIds = new ArrayList<Integer>();
while (rs.next()) {
  rsIds.add(rs.getInt(1));
}
return rsIds.toArray(new Integer[](rsIds.size());

It should automatically convert the Integer[] to an int[] for you via autoboxing.

---

Seeing as how I'm an idiot, and that doesn't work, this is how I would then do it:

rs.last();
int[] rsIds = new int[rs.getRow()];
rs.beforeFirst();
int counter = 0;
while (rs.next()) {
  rsIds[counter] = rs.getInt(1);
  counter++;
}

This won't work if the ResultSet is of type TYPE_FORWARD_ONLY, you would need to change the scroll type for it to work.

Answer 2

You need to add each result from the ResultSet to the array and for that you need a counter variable as the index of the array.

Also, initialize your int[] array properly because currently its just initialized to null .

int[] rsIDs = new int[size]; // decide the size
int counter = 0; // counter
while (rs.next()) {
    rsIDs[counter++] = rs.getInt(1);
}

And if you do not know the size before hand, then it is better to use an ArrayList instead of an array .

Answer 3

There are two ways to solve the problem:

1. Execute another query to extract size first, extract size and then create array of this size:

    String sizeQuery = "SELECT count(*) FROM " + Dbnum + ".tabName where ObjectID=?"; 

2. Create an List of Integer , add result to it (as M21B8 described), and then convert it to an int[] , as:

    int size = list.size(); int[] result = new int[size]; for (int i = 0; i < size; i++) { result[i] = list.get(i); } return result; 

Answer 4

You could make your life easier and use an ArrayList:

ResultSet rs = preparedStatement.executeQuery();      
ArrayList<Integer> rsIDs = new ArrayList<>();
while (rs.next()) {
    rsIDs.add(rs.getInt(1));
}

If you still want it in an array you can create it afterwards.