Java Iterator backed by a ResultSet

user_211496 0
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I've got a class that implements Iterator with a ResultSet as a data member. Essentially the class looks like this:

public class A implements Iterator{
    private ResultSet entities;
    ...
    public Object next(){
        entities.next();
        return new Entity(entities.getString...etc....)
    }

    public boolean hasNext(){
        //what to do?
    }
    ...
}

How can I check if the ResultSet has another row so I can create a valid hasNext method since ResultSet has no hasNext defined itself? I was thinking doing SELECT COUNT(*) FROM... query to get the count and managing that number to see if there's another row but I'd like to avoid this.

resultset jdbc iterator sql java
17 Answers

One option is the ResultSetIterator from the Apache DBUtils project.

BalusC rightly points out the the various concerns in doing this. You need to be very careful to properly handle the connection/resultset lifecycle. Fortunately, the DBUtils project also has solutions for safely working with resultsets.

If BalusC's solution is impractical for you (e.g. you are processing large datasets that can't all fit in memory) you might want to give it a shot.

user_1038140
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