Class AbstractBackEndDataProvider<T,​F>

Constructor Detail

• AbstractBackEndDataProvider

  public AbstractBackEndDataProvider()

Method Detail

• fetch

  public Stream<T> fetch​(Query<T,​F> query)

  Description copied from interface: DataProvider

  Fetches data from this DataProvider using given query.

  Depending on the use case this operation might open I/O channels.

  Consumers of the returned stream are responsible for closing it when all the stream operations are done to ensure that any resources feeding the stream are properly released. Failure to close an I/O stream might lead to resource leaks.

  It is strongly recommended to use a try-with-resources block to automatically close an I/O stream after its terminal operation has been executed. Below is an example of how to properly use and close the stream:

  
   try (Stream<T> stream = fetch(query)) {
       stream.forEach(System.out::println); // Example terminal operation
   }
   

  NOTE: This mainly concerns data providers where DataProvider.isInMemory() returns false. While it is technically possible to configure or extend an in-memory data provider in a way that compromises the in-memory nature, doing so is conceptually frowned upon. In applications that choose to do so regardless, the use of this pattern is strongly recommended even if DataProvider.isInMemory() returns true.

  The try-with-resources pattern is safe to use with this method even if you are unsure whether or not it returns an I/O stream, but it's unnecessary to apply the pattern to all stream handling everywhere. For most streams the only consumed resource is memory, and Java's built-in cleanup is sufficient to free it.

  With large data sets where memory consumption might become a problem it is recommended to use lazy data providers instead of in-memory ones. See e.g. DataProvider.fromCallbacks(FetchCallback, CountCallback) or BackEndDataProvider for more info.

  Specified by:

  fetch in interface DataProvider<T,​F>

  Parameters:

  query - given query to request data

  Returns:

  the result of the query request: a stream of data objects, not null

• size

  public int size​(Query<T,​F> query)

  Description copied from interface: DataProvider

  Gets the amount of data in this DataProvider.

  Specified by:

  size in interface DataProvider<T,​F>

  Parameters:

  query - query with sorting and filtering

  Returns:

  the size of the data provider

• fetchFromBackEnd

  protected abstract Stream<T> fetchFromBackEnd​(Query<T,​F> query)

  Fetches data from the back end using the given query.

  Parameters:

  query - the query that defines sorting, filtering and paging for fetching the data

  Returns:

  a stream of items matching the query

• sizeInBackEnd

  protected abstract int sizeInBackEnd​(Query<T,​F> query)

  Counts the number of items available in the back end.

  Parameters:

  query - the query that defines filtering to be used for counting the number of items

  Returns:

  the number of available items

• setSortOrders

  public void setSortOrders​(List<QuerySortOrder> sortOrders)

  Description copied from interface: BackEndDataProvider

  Sets a list of sort orders to use as the default sorting for this data provider. This overrides the sorting set by any other method that manipulates the default sorting of this data provider.

  The default sorting is used if the query defines no sorting. The default sorting is also used to determine the ordering of items that are considered equal by the sorting defined in the query.

  Specified by:

  setSortOrders in interface BackEndDataProvider<T,​F>

  Parameters:

  sortOrders - a list of sort orders to set, not null

  See Also:

  BackEndDataProvider.setSortOrder(QuerySortOrder)