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Filtering with Paging Predicates

Hazelcast provides paging for defined predicates. With its PagingPredicate class, you can get a collection of keys, values, or entries page by page by filtering them with predicates and giving the size of the pages. Also, you can sort the entries by specifying comparators.

In the example code below:

  • The greaterEqual predicate gets values from the "students" map. This predicate has a filter to retrieve the objects with a "age" greater than or equal to 18.
  • Then a PagingPredicate is constructed in which the page size is 5, so there will be 5 objects in each page. The first time the values are called creates the first page.
  • It gets subsequent pages with the nextPage() method of PagingPredicate and querying the map again with the updated PagingPredicate.
IMap<Integer, Student> map = hazelcastInstance.getMap( "students" );
Predicate greaterEqual = Predicates.greaterEqual( "age", 18 );
PagingPredicate pagingPredicate = new PagingPredicate( greaterEqual, 5 );
// Retrieve the first page
Collection<Student> values = map.values( pagingPredicate );
...
// Set up next page
pagingPredicate.nextPage();
// Retrieve next page
values = map.values( pagingPredicate );
...

If a comparator is not specified for PagingPredicate, but you want to get a collection of keys or values page by page, this collection must be an instance of Comparable (i.e. it must implement java.lang.Comparable). Otherwise, the java.lang.IllegalArgument exception is thrown.

Starting with Hazelcast 3.6, you can also access to a specific page more easily with the help of the method setPage(). By this way, if you make a query for 100th page, for example, it will get all the 100 pages at once instead of reaching the 100th page one by one using the method nextPage(). Please note that this feature tires the memory and refer to the PagingPredicate class.

Paging Predicate, also known as Order & Limit, is not supported in Transactional Context.

RELATED INFORMATION

Please see the Predicates class for all predicates provided.