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https://issues.apache.org/jira/browse/JENA-1427?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16257292#comment-16257292
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Adam Jacobs commented on JENA-1427:
-----------------------------------
The use case would be to consume only one element (or none) from the iterator.
{noformat}
RDFNode object = model.listObjectsOfProperty(subject, predicate).nextOrElse(()
-> {throw new IllegalStateException("No objects found for subject and
predicate...");});
{noformat}
Often I have an {{ExtendedIterator}} as a result of one of the list...()
methods on {{Model}} (listObjects, listResources, etc.).
I expect one matching element to a query. If no element is present, I would
like to throw a custom exception; otherwise, consume the element.
More rarely, there is a sensible default value in case no elements are found.
If multiple elements match the query, I do not need more than one.
Occasionally, multiple elements could be considered an exception as well; but
most often they do not matter.
Writing this comment made me realize that a {{Model}} method which takes a SPO
and returns an {{Optional}} might solve this case too; but there are so many
variations of list methods on Model, to provide a version of each one that
returns Optional.
> Add nextOrElse() method in ExtendedIterator
> -------------------------------------------
>
> Key: JENA-1427
> URL: https://issues.apache.org/jira/browse/JENA-1427
> Project: Apache Jena
> Issue Type: Improvement
> Components: Core
> Affects Versions: Jena 3.5.0
> Reporter: Adam Jacobs
> Priority: Trivial
> Labels: easytask
>
> Allow a functional approach for returning a default value or throwing a
> custom exception from a Jena iterator.
> The following method may be added to the ExtendedIterator interface.
> {noformat}
> /**
> Answer the next object, if it exists, otherwise invoke the
> _supplier_.
> */
> public default T nextOrElse( Supplier<T> supplier ) {
> return hasNext() ? next() : supplier.get();
> }
> {noformat}
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