common/org.eclipse.tracecompass.common.core/src/org/eclipse/tracecompass/common/core/StreamUtils.java

   1 /*******************************************************************************
   2  * Copyright (c) 2016 EfficiOS Inc., Alexandre Montplaisir
   3  *
   4  * All rights reserved. This program and the accompanying materials
   5  * are made available under the terms of the Eclipse Public License v1.0
   6  * which accompanies this distribution, and is available at
   7  * http://www.eclipse.org/legal/epl-v10.html
   8  *******************************************************************************/
   9
  10 package org.eclipse.tracecompass.common.core;
  11
  12 import static org.eclipse.tracecompass.common.core.NonNullUtils.checkNotNull;
  13
  14 import java.util.function.Function;
  15 import java.util.stream.Stream;
  16 import java.util.stream.StreamSupport;
  17
  18 /**
  19  * Common utilities for {@link Stream}.
  20  *
  21  * @author Alexandre Montplaisir
  22  * @since 2.0
  23  */
  24 public final class StreamUtils {
  25
  26     private StreamUtils() {}
  27
  28     /**
  29      * Get a sequential {@link Stream} from an {@link Iterable}.
  30      *
  31      * @param iterable
  32      *            Any iterable
  33      * @return The stream on the elements of the iterable
  34      */
  35     public static <T> Stream<T> getStream(Iterable<T> iterable) {
  36         return StreamSupport.stream(iterable.spliterator(), false);
  37     }
  38
  39     /**
  40      * Generic utility class to "flatten" a data structure using the
  41      * {@link Stream} API.
  42      *
  43      * @param <T>
  44      *            The type of container, or "node" in the tree
  45      */
  46     public static class StreamFlattener<T> {
  47
  48         private final Function<T, Stream<T>> fGetChildrenFunction;
  49
  50         /**
  51          * Constructor
  52          *
  53          * @param getChildrenFunction
  54          *            The function to use to get each element's children. Should
  55          *            return a {@link Stream} of those children.
  56          */
  57         public StreamFlattener(Function<T, Stream<T>> getChildrenFunction) {
  58             fGetChildrenFunction = getChildrenFunction;
  59         }
  60
  61         /**
  62          * Do an in-order flattening of the data structure, starting at the given
  63          * element (or node).
  64          *
  65          * @param element
  66          *            The tree node or similar from which to start
  67          * @return A unified Stream of all the children that were found,
  68          *         recursively.
  69          */
  70         public Stream<T> flatten(T element) {
  71             Stream<T> ret = Stream.concat(
  72                     Stream.of(element),
  73                     fGetChildrenFunction.apply(element).flatMap(this::flatten));
  74             return checkNotNull(ret);
  75         }
  76     }
  77 }