org.calrissian.mango.collect

Class CloseableIterables

java.lang.Object

org.calrissian.mango.collect.CloseableIterables

public class CloseableIterables
extends Object

Utility class to develop commonly used closeable iterables functions.

Method Summary

Methods

Modifier and Type	Method and Description
static <T> CloseableIterable<T>	autoClose(CloseableIterable<? extends T> iterable) Autoclose the iterable when its iterator is exhausted or if an exception is thrown.
static <T> CloseableIterable<T>	chain(CloseableIterable<? extends T>... iterables) Combines multiple closeable iterables into a single closeable iterable.
static <T> CloseableIterable<T>	chain(Iterable<? extends CloseableIterable<? extends T>> iterables) Combines multiple closeable iterables into a single closeable iterable.
static <T> CloseableIterable<T>	concat(CloseableIterable<? extends Iterable<? extends T>> inputs) Combines multiple iterables into a single closeable iterable.
static <T> CloseableIterable<T>	cycle(CloseableIterable<T> iterable) Returns a closeable iterable whose iterators cycle indefinitely over the elements of iterable.
static <T> CloseableIterable<T>	distinct(CloseableIterable<T> iterable) If we can assume the closeable iterable is sorted, return the distinct elements.
static <T> CloseableIterable<T>	emptyIterable() Returns an empty closeable iterable
static <T> CloseableIterable<T>	filter(CloseableIterable<?> iterable, Class<T> type) Returns all instances of class type in unfiltered.
static <T> CloseableIterable<T>	filter(CloseableIterable<T> iterable, Predicate<? super T> filter) Returns the elements of unfiltered that satisfy a predicate.
static <T> CloseableIterable<List<T>>	groupBy(CloseableIterable<? extends T> iterable, Function<? super T,?> groupingFunction) Divides an iterable into unmodifiable sublists of equivalent elements.
static <T> CloseableIterable<T>	limit(CloseableIterable<T> iterable, int limitSize) Creates a closeable iterable with the first limitSize elements of the given closeable iterable.
static <T> CloseableIterable<List<T>>	paddedParition(CloseableIterable<T> iterable, int size) Divides a closeable iterable into unmodifiable sublists of the given size, padding the final list with null values if necessary.
static <T> CloseableIterable<List<T>>	partition(CloseableIterable<T> iterable, int size) Divides a closeable iterable into unmodifiable sublists of the given size (the final iterable may be smaller).
static <T> CloseableIterable<T>	singleton(T value) Returns a closeable iterable containing only value.
static <T> CloseableIterable<T>	skip(CloseableIterable<T> iterable, int numberToSkip) Returns a view of iterable that skips its first numberToSkip elements.
static <F,T> CloseableIterable<T>	transform(CloseableIterable<F> iterable, Function<? super F,? extends T> function) Returns an iterable that applies function to each element of fromIterable.
static <T> CloseableIterable<T>	wrap(Iterable<T> iterable) Creates a CloseableIterable from a standard iterable.

Methods inherited from class java.lang.Object

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

Method Detail

distinct

public static <T> CloseableIterable<T> distinct(CloseableIterable<T> iterable)

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

groupBy

public static <T> CloseableIterable<List<T>> groupBy(CloseableIterable<? extends T> iterable,
                                     Function<? super T,?> groupingFunction)

Divides an iterable into unmodifiable sublists of equivalent elements. The iterable groups elements in consecutive order, forming a new partition when the value from the provided function changes. For example, grouping the iterable [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> CloseableIterable<T> concat(CloseableIterable<? extends Iterable<? extends T>> inputs)

Combines multiple iterables into a single closeable iterable. The returned closeable iterable has an iterator that traverses the elements of each iterable in inputs. The input iterators are not polled until necessary.

cycle

public static <T> CloseableIterable<T> cycle(CloseableIterable<T> iterable)

Returns a closeable iterable whose iterators cycle indefinitely over the elements of iterable.

That iterator supports remove() if iterable.iterator() does. After remove() is called, subsequent cycles omit the removed element, which is no longer in iterable. The iterator's hasNext() method returns true until iterable is empty.

Warning: Typical uses of the resulting iterator may produce an infinite loop. You should use an explicit break or be certain that you will eventually remove all the elements. The close method should be expicitly called when done with iteration. Tools such as CloseableIterables.autoClose() will not work.

filter

public static <T> CloseableIterable<T> filter(CloseableIterable<?> iterable,
                              Class<T> type)

Returns all instances of class type in unfiltered. The returned closeable iterable has elements whose class is type or a subclass of type. The returned iterable's iterator does not support remove().

filter

public static <T> CloseableIterable<T> filter(CloseableIterable<T> iterable,
                              Predicate<? super T> filter)

Returns the elements of unfiltered that satisfy a predicate. The resulting closeable iterable's iterator does not support remove().

limit

public static <T> CloseableIterable<T> limit(CloseableIterable<T> iterable,
                             int limitSize)

Creates a closeable iterable with the first limitSize elements of the given closeable iterable. If the original closeable iterable does not contain that many elements, the returned iterator will have the same behavior as the original closeable iterable. The returned closeable iterable's iterator supports remove() if the original iterator does.

paddedParition

public static <T> CloseableIterable<List<T>> paddedParition(CloseableIterable<T> iterable,
                                            int size)

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

Iterators returned by the returned closeableiterable do not support the Iterator.remove() method.

partition

public static <T> CloseableIterable<List<T>> partition(CloseableIterable<T> iterable,
                                       int size)

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

Iterators returned by the returned iterable do not support the Iterator.remove() method.

skip

public static <T> CloseableIterable<T> skip(CloseableIterable<T> iterable,
                            int numberToSkip)

Returns a view of iterable that skips its first numberToSkip elements. If iterable contains fewer than numberToSkip elements, the returned closeableiterable skips all of its elements.

Modifications to the underlying CloseableIterable before a call to iterator() are reflected in the returned iterator. That is, the iterator skips the first numberToSkip elements that exist when the Iterator is created, not when skip() is called.

The returned closeableiterable's iterator supports remove() if the iterator of the underlying iterable supports it. Note that it is not possible to delete the last skipped element by immediately calling remove() on that iterator, as the Iterator contract states that a call to remove() before a call to next() will throw an IllegalStateException.

transform

public static <F,T> CloseableIterable<T> transform(CloseableIterable<F> iterable,
                                   Function<? super F,? extends T> function)

Returns an iterable that applies function to each element of fromIterable.

chain

@SafeVarargs
public static <T> CloseableIterable<T> chain(CloseableIterable<? extends T>... iterables)

Combines multiple closeable iterables into a single closeable iterable. The returned closeable iterable has an iterator that traverses the elements of each iterable in inputs. The input iterators are not polled until necessary.

chain

public static <T> CloseableIterable<T> chain(Iterable<? extends CloseableIterable<? extends T>> iterables)

Combines multiple closeable iterables into a single closeable iterable. The returned closeable iterable has an iterator that traverses the elements of each iterable in inputs. The input iterators are not polled until necessary.

autoClose

public static <T> CloseableIterable<T> autoClose(CloseableIterable<? extends T> iterable)

Autoclose the iterable when its iterator is 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(iterable), 1) will not close the resource if there is more than 1 element, but autoClose(limit(iterable, 1)) will close the underlying resource.

emptyIterable

public static <T> CloseableIterable<T> emptyIterable()

Returns an empty closeable iterable

The equivalent of this method is Collections.emptySet().

singleton

public static <T> CloseableIterable<T> singleton(T value)

Returns a closeable iterable containing only value.

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

wrap

public static <T> CloseableIterable<T> wrap(Iterable<T> iterable)

Creates a CloseableIterable from a standard iterable. If iterable is already a CloseableIterable it will simply be returned as is.