Java – How to retrieve a JDBC ResultSet as an ArrayList

arraylistjavajdbcperformanceresultset

I'm doing a query to retrieve a large amount of IDs (integers). Instead of iterating millions of times through the ResultSet and copying everything one-by-one to an ArrayList, is there some way to simply retrieve everything as an ArrayList?

I understand that ResultSet is supposed to be iterated because the underlying implementation may be caching stuff, but in my situation I just need all the IDs straight away. I know I can set the FetchSize to a large number, but then I still have to retrieve the IDs one-by-one.

Clarification: the reason I want to do this is performance. Profiling shows me that doing ResultSet.next(), ResultSet.getInt() and ArrayList.add() millions of times takes quite some time. I figure that the database (I'm using H2, which is written in Java) probably has the array or list somewhere in memory, so I'm looking for a way to have it copied to me directly instead of through the ResultSet iterating interface.

Best Answer

Using the Apache DbUtils library you can easily return a ResultSet as a List of Maps.

public List query(String query) {
    List result = null;
    try {
        QueryRunner qrun = new QueryRunner();
        result = (List) qrun.query(connection, query, new MapListHandler());
    } catch (Exception ex) {
        ex.printStackTrace();
    }
    return result;
}
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