在ResultSet Java中对数据进行排序

Question

I have obtained a ResultSet for some query, eg:

select * from students order by roll 

Now, is it possible to perform an equivalent of query

Select * from students order by dob;`

on the ResultSet ?

Answer 1

As rule of thumb (well, almost) everything that can be done in the DB should be done there, so you should sort your data in the DB using the ... ORDER BY <column1>, <COLUMN2>... ASC/DESC

But if for some reason you cannot do that you should extract all the data from the RS into a collection (and may be map your data to domain objects) and sort it using the Collections.sort() method with an appropriate Comparator

Answer 2

It will be very not recommended to do the Sort after the query (ie. When you're getting the ResultSet). You should always aim to do actions on the SQL Server rather on the code itself.

ResultSet are some kind of Iteration objects, that means that you can only move one by one. Thus, in order to Sort it, you first need to shift the data into a Collection and only then use Sorting on it. Compare to SQL Sorting this is overhead and can be avoided.

Answer 3

Get an ArrayList from your ResultSet by iterating over your result and adding it to aa new list. Then use Collections.sort(Collection, Comparator) to sort your result