org.calrissian.mango.collect

Class CloseableIterators

java.lang.Object

org.calrissian.mango.collect.CloseableIterators

public class CloseableIterators
extends Object

Utility class to develop commonly used closeable iterator functions.

Method Summary

Modifier and Type	Method and Description
static <T> CloseableIterator<T>	autoClose(CloseableIterator<? extends T> iterator) Autoclose the iterator when exhausted or if an exception is thrown.
static <T> CloseableIterator<T>	chain(CloseableIterator<? extends T>... iterators) Combines multiple closeable iterators into a single closeable iterator.
static <T> CloseableIterator<T>	chain(Iterator<? extends CloseableIterator<? extends T>> iterator) Combines multiple closeable iterators into a single closeable iterator.
static <T> CloseableIterator<T>	concat(CloseableIterator<? extends Iterator<? extends T>> iterators) Combines multiple iterators into a single closeable iterator.
static <T> CloseableIterator<T>	distinct(CloseableIterator<T> iterator) If we can assume the closeable iterator is sorted, return the distinct elements.
static <T> CloseableIterator<T>	emptyIterator() Returns an empty closeable iterator.
static <T> CloseableIterator<T>	filter(CloseableIterator<?> iterator, Class<T> type) Returns all instances of class type in unfiltered.
static <T> CloseableIterator<T>	filter(CloseableIterator<T> iterator, Predicate<T> filter) Returns the elements of unfiltered that satisfy a predicate.
static <T> CloseableIterator<List<T>>	groupBy(CloseableIterator<? extends T> iterator, Function<? super T,?> groupingFunction) Divides a closeableiterator into unmodifiable sublists of equivalent elements.
static <T> CloseableIterator<T>	limit(CloseableIterator<T> iterator, int limitSize) Creates a closeable iterator returning the first limitSize elements of the given closeable iterator.
static <T> CloseableIterator<List<T>>	paddedParition(CloseableIterator<T> iterator, int size) Divides a closeableiterator into unmodifiable sublists of the given size, padding the final iterator with null values if necessary.
static <T> CloseableIterator<List<T>>	partition(CloseableIterator<T> iterator, int size) Divides a closeableiterator into unmodifiable sublists of the given size (the final list may be smaller).
static <T> PeekingCloseableIterator<T>	peekingIterator(CloseableIterator<T> iterator) Returns a PeekingCloseableIterator backed by the given closeable iterator.
static <T> CloseableIterator<T>	singletonIterator(T value) Returns an iterator containing only value.
static <F,T> CloseableIterator<T>	transform(CloseableIterator<F> iterator, Function<F,T> function) Returns a closeable iterator that applies function to each element of fromIterator.
static <T> CloseableIterator<T>	wrap(Iterator<T> iterator) Creates a CloseableIterator from a standard iterator.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

distinct

public static <T> CloseableIterator<T> distinct(CloseableIterator<T> iterator)

If we can assume the closeable iterator is sorted, return the distinct elements. This only works if the data provided is sorted.

groupBy

public static <T> CloseableIterator<List<T>> groupBy(CloseableIterator<? extends T> iterator,
                                                     Function<? super T,?> groupingFunction)

Divides a closeableiterator into unmodifiable sublists of equivalent elements. The iterator groups elements in consecutive order, forming a new partition when the value from the provided function changes. For example, grouping the iterator [1, 3, 2, 4, 5] with a function grouping even and odd numbers yields [[1, 3], [2, 4], [5] all in the original order.

The returned lists implement RandomAccess.

concat

public static <T> CloseableIterator<T> concat(CloseableIterator<? extends Iterator<? extends T>> iterators)

Combines multiple iterators into a single closeable iterator. The returned closeable iterator iterates across the elements of each iterator in inputs. The input iterators are not polled until necessary.

emptyIterator

public static <T> CloseableIterator<T> emptyIterator()

Returns an empty closeable iterator.

filter

public static <T> CloseableIterator<T> filter(CloseableIterator<T> iterator,
                                              Predicate<T> filter)

Returns the elements of unfiltered that satisfy a predicate.

filter

public static <T> CloseableIterator<T> filter(CloseableIterator<?> iterator,
                                              Class<T> type)

Returns all instances of class type in unfiltered. The returned closeable iterator has elements whose class is type or a subclass of type.

limit

public static <T> CloseableIterator<T> limit(CloseableIterator<T> iterator,
                                             int limitSize)

Creates a closeable iterator returning the first limitSize elements of the given closeable iterator. If the original closeable iterator does not contain that many elements, the returned closeable iterator will have the same behavior as the original.

paddedParition

public static <T> CloseableIterator<List<T>> paddedParition(CloseableIterator<T> iterator,
                                                            int size)

Divides a closeableiterator into unmodifiable sublists of the given size, padding the final iterator with null values if necessary. For example, partitioning a closeable iterator containing [a, b, c, d, e] with a partition size of 3 yields [[a, b, c], [d, e, null]] -- an outer iterator containing two inner lists of three elements each, all in the original order.

The returned lists implement RandomAccess.

partition

public static <T> CloseableIterator<List<T>> partition(CloseableIterator<T> iterator,
                                                       int size)

Divides a closeableiterator into unmodifiable sublists of the given size (the final list may be smaller). For example, partitioning a closeableiterator containing [a, b, c, d, e] with a partition size of 3 yields [[a, b, c], [d, e]] -- an outer iterator containing two inner lists of three and two elements, all in the original order.

The returned lists implement RandomAccess.

peekingIterator

public static <T> PeekingCloseableIterator<T> peekingIterator(CloseableIterator<T> iterator)

Returns a PeekingCloseableIterator backed by the given closeable iterator.

Calls to peek do not change the state of the iterator. The subsequent call to next after peeking will always return the same value.

singletonIterator

public static <T> CloseableIterator<T> singletonIterator(T value)

Returns an iterator containing only value.

The Iterable equivalent of this method is Collections.singleton(T).

transform

public static <F,T> CloseableIterator<T> transform(CloseableIterator<F> iterator,
                                                   Function<F,T> function)

Returns a closeable iterator that applies function to each element of fromIterator.

chain

@SafeVarargs
public static <T> CloseableIterator<T> chain(CloseableIterator<? extends T>... iterators)

Combines multiple closeable iterators into a single closeable iterator. The returned closeable iterator iterates across the elements of each closeable iterator in inputs. The input iterators are not polled until necessary.

As each closeable iterator is exhausted, it is closed before moving onto the next closeable iterator. A call to close on the returned closeable iterator will quietly close all of the closeable iterators in inputs which have not been exhausted.

chain

public static <T> CloseableIterator<T> chain(Iterator<? extends CloseableIterator<? extends T>> iterator)

Combines multiple closeable iterators into a single closeable iterator. The returned closeable iterator iterates across the elements of each closeable iterator in inputs. The input iterators are not polled until necessary.

As each closeable iterator is exhausted, it is closed before moving onto the next closeable iterator. A call to close on the returned closeable iterator will quietly close all of the closeable iterators in inputs which have not been exhausted.

autoClose

public static <T> CloseableIterator<T> autoClose(CloseableIterator<? extends T> iterator)

Autoclose the iterator when exhausted or if an exception is thrown.

Note that when using this method the order of calls matters. limit() is an example of one method which can prevent the completion of an iterator. For instance limit(autoClose(iterator), 1) will not close the resource if there is more than 1 element, but autoClose(limit(iterator, 1)) will close the underlying resource.

wrap

public static <T> CloseableIterator<T> wrap(Iterator<T> iterator)

Creates a CloseableIterator from a standard iterator.