Java tutorial
/* * Copyright (C) 2013 The Calrissian Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.calrissian.mango.collect; import com.google.common.base.Function; import com.google.common.base.Optional; import com.google.common.base.Predicate; import com.google.common.collect.*; import java.io.IOException; import java.util.Collection; import java.util.Comparator; import java.util.Iterator; import static com.google.common.base.Preconditions.checkNotNull; /** * A class to provide the same basic functionality as {@link com.google.common.collect.FluentIterable} to work * with {@link CloseableIterable}s */ public abstract class FluentCloseableIterable<T> extends AbstractCloseableIterable<T> { protected FluentCloseableIterable() { } /** * The rest of the methods are taken from guava directly */ public static <E> FluentCloseableIterable<E> from(final CloseableIterable<E> iterable) { return (iterable instanceof FluentCloseableIterable) ? (FluentCloseableIterable<E>) iterable : new FluentCloseableIterable<E>() { @Override protected void doClose() throws IOException { iterable.close(); } @Override protected Iterator<E> retrieveIterator() { return iterable.iterator(); } }; } /** * Returns a fluent iterable where the underlying resources are automatically closed when its iterator has been * exhausted. * * Note that when using this method the order of calls matters. {@code limit()} is an example of one method which can * prevent the completion of an iterator. For instance from(iterable).autoClose().limit(1) will not close the * resource if there is more than 1 element, but from(iterable).limit(1).autoClose() will close the underlying * resource. */ public FluentCloseableIterable<T> autoClose() { return from(CloseableIterables.autoClose(this)); } /** * Returns a string representation of this fluent iterable, with the format * {@code [e1, e2, ..., en]}. */ @Override public String toString() { return Iterables.toString(this); } /** * Returns the number of elements in this fluent iterable. */ public final int size() { return Iterables.size(this); } /** * Returns {@code true} if this fluent iterable contains any object for which * {@code equals(element)} is true. */ public final boolean contains(Object element) { return Iterables.contains(this, element); } /** * Returns a fluent iterable whose {@code Iterator} cycles indefinitely over the elements of * this fluent iterable. * * <p>That iterator supports {@code remove()} if {@code iterable.iterator()} does. After * {@code remove()} is called, subsequent cycles omit the removed element, which is no longer in * this fluent iterable. The iterator's {@code hasNext()} method returns {@code true} until * this fluent iterable is empty. * * <p><b>Warning:</b> Typical uses of the resulting iterator may produce an infinite loop. You * should use an explicit {@code break} or be certain that you will eventually remove all the * elements. */ public final FluentCloseableIterable<T> cycle() { return from(CloseableIterables.cycle(this)); } /** * Returns the elements from this fluent iterable that satisfy a predicate. The * resulting fluent iterable's iterator does not decorator {@code remove()}. */ public final FluentCloseableIterable<T> filter(Predicate<? super T> predicate) { return from(CloseableIterables.filter(this, predicate)); } /** * Returns the elements from this fluent iterable that are instances of class {@code type}. * * @param type the type of elements desired */ public final <E> FluentCloseableIterable<E> filter(Class<E> type) { return from(CloseableIterables.filter(this, type)); } /** * Returns {@code true} if any element in this fluent iterable satisfies the predicate. */ public final boolean anyMatch(Predicate<? super T> predicate) { return Iterables.any(this, predicate); } /** * Returns {@code true} if every element in this fluent iterable satisfies the predicate. * If this fluent iterable is empty, {@code true} is returned. */ public final boolean allMatch(Predicate<? super T> predicate) { return Iterables.all(this, predicate); } /** * Returns an {@link com.google.common.base.Optional} containing the first element in this fluent iterable that * satisfies the given predicate, if such an element exists. * * <p><b>Warning:</b> avoid using a {@code predicate} that matches {@code null}. If {@code null} * is matched in this fluent iterable, a {@link NullPointerException} will be thrown. */ public final Optional<T> firstMatch(Predicate<? super T> predicate) { return Iterables.tryFind(this, predicate); } /** * Returns a fluent iterable that applies {@code function} to each element of this * fluent iterable. * * <p>The returned fluent iterable's iterator supports {@code remove()} if this iterable's * iterator does. After a successful {@code remove()} call, this fluent iterable no longer * contains the corresponding element. */ public final <E> FluentCloseableIterable<E> transform(Function<? super T, ? extends E> function) { return from(CloseableIterables.transform(this, function)); } /** * Applies {@code function} to each element of this fluent iterable and returns * a fluent iterable with the concatenated combination of results. {@code function} * returns an Iterable of results. * * <p>The returned fluent iterable's iterator supports {@code remove()} if this * function-returned iterables' iterator does. After a successful {@code remove()} call, * the returned fluent iterable no longer contains the corresponding element. */ public <E> FluentCloseableIterable<E> transformAndConcat(Function<? super T, ? extends Iterable<E>> function) { return from(CloseableIterables.concat(transform(function))); } /** * Returns an {@link Optional} containing the first element in this fluent iterable. * If the iterable is empty, {@code Optional.absent()} is returned. * * @throws NullPointerException if the first element is null; if this is a possibility, use * {@code iterator().next()} or {@link Iterables#getFirst} instead. */ public final Optional<T> first() { Iterator<T> iterator = this.iterator(); return iterator.hasNext() ? Optional.of(iterator.next()) : Optional.<T>absent(); } /** * Returns an {@link Optional} containing the last element in this fluent iterable. * If the iterable is empty, {@code Optional.absent()} is returned. * * @throws NullPointerException if the last element is null; if this is a possibility, use * {@link Iterables#getLast} instead. */ public final Optional<T> last() { // Iterables#getLast was inlined here so we don't have to throw/catch a NSEE Iterator<T> iterator = this.iterator(); if (!iterator.hasNext()) { return Optional.absent(); } while (true) { T current = iterator.next(); if (!iterator.hasNext()) { return Optional.of(current); } } } /** * Returns a view of this fluent iterable that skips its first {@code numberToSkip} * elements. If this fluent iterable contains fewer than {@code numberToSkip} elements, * the returned fluent iterable skips all of its elements. * * <p>Modifications to this fluent iterable before a call to {@code iterator()} are * reflected in the returned fluent iterable. That is, the its iterator skips the first * {@code numberToSkip} elements that exist when the iterator is created, not when {@code skip()} * is called. * * <p>The returned fluent iterable's iterator supports {@code remove()} if the * {@code Iterator} of this fluent iterable supports it. Note that it is <i>not</i> * possible to delete the last skipped element by immediately calling {@code remove()} on the * returned fluent iterable's iterator, as the {@code Iterator} contract states that a call * to {@code * remove()} before a call to {@code next()} will throw an * {@link IllegalStateException}. */ public final FluentCloseableIterable<T> skip(int numberToSkip) { return from(CloseableIterables.skip(this, numberToSkip)); } /** * Creates a fluent iterable with the first {@code size} elements of this * fluent iterable. If this fluent iterable does not contain that many elements, * the returned fluent iterable will have the same behavior as this fluent iterable. * The returned fluent iterable's iterator supports {@code remove()} if this * fluent iterable's iterator does. * * @param size the maximum number of elements in the returned fluent iterable * @throws IllegalArgumentException if {@code size} is negative */ public final FluentCloseableIterable<T> limit(int size) { return from(CloseableIterables.limit(this, size)); } /** * Determines whether this fluent iterable is empty. */ public final boolean isEmpty() { return !this.iterator().hasNext(); } /** * Returns an {@code ImmutableList} containing all of the elements from this * fluent iterable in proper sequence. */ public final ImmutableList<T> toList() { return ImmutableList.copyOf(this); } /** * Returns an {@code ImmutableList} containing all of the elements from this * {@code FluentCloseableIterable} in the order specified by {@code comparator}. To produce an * {@code ImmutableList} sorted by its natural ordering, use * {@code toSortedImmutableList(Ordering.natural())}. * * @param comparator the function by which to sort list elements * @throws NullPointerException if any element is null */ public final ImmutableList<T> toSortedList(Comparator<? super T> comparator) { return Ordering.from(comparator).immutableSortedCopy(this); } /** * Returns an {@code ImmutableSet} containing all of the elements from this * fluent iterable with duplicates removed. */ public final ImmutableSet<T> toSet() { return ImmutableSet.copyOf(this); } /** * Returns an {@code ImmutableSortedSet} containing all of the elements from this * {@code FluentCloseableIterable} in the order specified by {@code comparator}, with duplicates * (determined by {@code comaprator.compare(x, y) == 0}) removed. To produce an * {@code ImmutableSortedSet} sorted by its natural ordering, use * {@code toImmutableSortedSet(Ordering.natural())}. * * @param comparator the function by which to sort set elements * @throws NullPointerException if any element is null */ public final ImmutableSortedSet<T> toSortedSet(Comparator<? super T> comparator) { return ImmutableSortedSet.copyOf(comparator, this); } /** * Returns an immutable map for which the elements of this {@code FluentIterable} are the keys in * the same order, mapped to values by the given function. If this iterable contains duplicate * elements, the returned map will contain each distinct element once in the order it first * appears. * * @throws NullPointerException if any element of this iterable is {@code null}, or if {@code * valueFunction} produces {@code null} for any key */ public final <V> ImmutableMap<T, V> toMap(Function<? super T, V> valueFunction) { return Maps.toMap(this, valueFunction); } /** * Creates an index {@code ImmutableListMultimap} that contains the results of applying a * specified function to each item in this {@code FluentIterable} of values. Each element of this * iterable will be stored as a value in the resulting multimap, yielding a multimap with the same * size as this iterable. The key used to store that value in the multimap will be the result of * calling the function on that value. The resulting multimap is created as an immutable snapshot. * In the returned multimap, keys appear in the order they are first encountered, and the values * corresponding to each key appear in the same order as they are encountered. * * @param keyFunction the function used to produce the key for each value * @throws NullPointerException if any of the following cases is true: * <ul> * <li>{@code keyFunction} is null * <li>An element in this fluent iterable is null * <li>{@code keyFunction} returns {@code null} for any element of this iterable * </ul> */ public final <K> ImmutableListMultimap<K, T> index(Function<? super T, K> keyFunction) { return Multimaps.index(this, keyFunction); } /** * Returns an immutable map for which the {@link java.util.Map#values} are the elements of this * {@code FluentIterable} in the given order, and each key is the product of invoking a supplied * function on its corresponding value. * * @param keyFunction the function used to produce the key for each value * @throws IllegalArgumentException if {@code keyFunction} produces the same key for more than one * value in this fluent iterable * @throws NullPointerException if any element of this fluent iterable is null, or if * {@code keyFunction} produces {@code null} for any value */ public final <K> ImmutableMap<K, T> uniqueIndex(Function<? super T, K> keyFunction) { return Maps.uniqueIndex(this, keyFunction); } /** * Returns an array containing all of the elements from this fluent iterable in iteration order. * * @param type the type of the elements * @return a newly-allocated array into which all the elements of this fluent iterable have * been copied */ public final T[] toArray(Class<T> type) { return Iterables.toArray(this, type); } /** * Copies all the elements from this fluent iterable to {@code collection}. This is equivalent to * calling {@code Iterables.addAll(collection, this)}. * * @param collection the collection to copy elements to * @return {@code collection}, for convenience */ public final <C extends Collection<? super T>> C copyInto(C collection) { checkNotNull(collection); for (T item : this) { collection.add(item); } return collection; } /** * Returns the element at the specified position in this fluent iterable. * * @param position position of the element to return * @return the element at the specified position in this fluent iterable * @throws IndexOutOfBoundsException if {@code position} is negative or greater than or equal to * the size of this fluent iterable */ public final T get(int position) { return Iterables.get(this, position); } /** * Returns a generic iterable with no beanlike properties such as {@code isEmpty()}. This is useful with libraries * that use reflection to determine bean definitions such as Jackson. * * Note this will prevent access to close the underlying resource. It is suggested that {@code autoClose()} be used * before calling this method. */ public final Iterable<T> toSimpleIterable() { return Iterables2.simpleIterable(this); } }