Building resultset using collection object

Question

Hi,

I had an issue in building the resultset using java. Here it goes...

I am storing a collection object which is organized as row wise taken from a resultset object and putting the collection object(which is stored as vector/array list) in cache and trying to retrieve the same collection object. Here i need to build back the resultset again using the collection object. Now my doubt is building the resultset in this way possible or not? Please let me know asap.

Thanks in advance,

Bhaskar

Answer 1

From what I could get, your code may be like this:

List collection = new ArrayList();
collection.add(" A collection in some order");

List cache = new ArrayList();
cache.add(collection); ...

Now when you retrieve I think you'll get your collection in order, since you have used List.

If this is not what you were expecting, do comment.

Answer 2

The best idea if you are using a collection in place of a cache is to use a CachedRowSet instead of a ResultSet. CachedRowSet is a Subinterface of ResultSet, but the data is already cached. This is far simpler than to write all the data into an ArrayList.
CachedRowSets can also be queried themselves.

CachedRowSet rs;
.......................
.......................
Integer id;
String name;

while (rs.next())
{      
     if (rs.getInt("id") == 13)
     {
          id   = rs.getInt("id");
          name = rs.getString("name")); 
     }     
}

So you just call the CachedRowSet whenever you need the info. It's almost as good as sliced bread. :)

EDIT:
There are no set methods for ResultSet, while there are Update methods. The problem with using the Update method's for the purpose of rebuilding a ResultSet is that it requires selecting a Row to update. Once the ResultSet has freed itself, all rows are set to null. A null reference cannot be called. A List of Lists mimics a ResultSet itself, or more correctly, an array of arrays mimic a ResultSet.

While Vectors are thread safe, there is a huge overhead attached to them. Use the ArrayList instead. As each nested List is created and placed into the outer nest List, insert it in this manner.

nest.add(Collections.unmodifiableList(nested));

After all of the nested Lists are inserted, return the nest List as an umodifiableList as well. This will give you a thread-safe collection without the overhead of the vectors.

Answer 3

I will advise you to use CachedRowSet. Refer http://www.onjava.com/pub/a/onjava/2004/06/23/cachedrowset.html this article to know more about CachedRowSet. Once you create this CachedRowSet, you can disconnect from the database, make some changes to the cached data and letter can even open the DB connection and commit the changes back to the Database.

Answer 4

Another option you should consider is just to refactor your code to accept a Collection instead of a ResultSet.

I'm assuming you pass that ResultSet to a method that iterates over it. You might as well change the method to iterate over an ArrayList...