CODEWITHSUNDEEP
sparqljena
Semantic web
Semantic web

Reputation: 43

semantic web - jena sparql

After excecuting a query in sparql jena, I tried to get the query result as a list, so I used this:

res = ResultSetFormatter.toList(results);

but when I write this method before that method the variable res returns null.

ResultSetFormatter.out(System.out, results);
res = ResultSetFormatter.toList(results);

I don't know what is the problem.

Upvotes: 2

Views: 595

Answers (2)

MikeJ
MikeJ

Reputation: 552

The main ResultSet implementation is com.hp.hpl.jena.sparql.engine.ResultSetStream which can only be used once, whereas you are trying to use it twice. The API documentation for ResultSetStream says:

The main ResultSet implementation for returning results from queries. This version is "use once" - you can not reset the result set because the results of the query are not remembered so as not to consume potentially large amounts of memory.

Upvotes: 3

Jeen Broekstra
Jeen Broekstra

Reputation: 22053

At a guess, I'd say ResultSetFormatter.out(ResultSet) consumes the ResultSet. So after this method has completed, ResultSet is empty.

It's somewhat comparable to how an Iterator works: once you've iterated over all the elements, the iterator is empty.

Upvotes: 2

Related Questions