IteratorDataSourceImpl.java

public class IteratorDataSourceImpl implements IteratorDataSource {

  private PagedDataSource pagedDataSource;

  @Override
  public Iterator<Entity> getAllEntities() {
    return new PagedIterator(Paging.firstPage(), (Paging paging) -> pagedDataSource.getEntities(paging).iterator());
  }

  private static class PagedIterator implements Iterator<Entity> {

    private final Function<Paging, Iterator<Entity>> iteratorProvider;
    private Paging currentPage;
    private Iterator<Entity> currentIterator;

    PagedIterator(Paging initialPage, Function<Paging, Iterator<Entity>> iteratorProvider) {
      currentPage = initialPage;
      this.iteratorProvider = iteratorProvider;
      currentIterator = iteratorProvider.apply(currentPage);
    }

    @Override
    public boolean hasNext() {
      if(currentIterator.hasNext()) {
        return true;
      } else {
        currentPage = currentPage.next();
        currentIterator = iteratorProvider.apply(currentPage);
        return currentIterator.hasNext();
      }
    }

    @Override
    public Entity next() {
      return currentIterator.next();
    }
  }
}