From 2ea44b2adae8da8e3e7f55cc226479f9431feda9 Mon Sep 17 00:00:00 2001 From: Jochen Wiedmann Date: Sun, 26 Jan 2020 22:57:13 +0100 Subject: [PATCH] - Added the Streams class. - Added Functions.stream() as an accessor method. --- src/changes/changes.xml | 1 + .../org/apache/commons/lang3/Functions.java | 37 ++ .../org/apache/commons/lang3/Streams.java | 380 ++++++++++++++++++ .../org/apache/commons/lang3/StreamsTest.java | 176 ++++++++ 4 files changed, 594 insertions(+) create mode 100644 src/main/java/org/apache/commons/lang3/Streams.java create mode 100644 src/test/java/org/apache/commons/lang3/StreamsTest.java diff --git a/src/changes/changes.xml b/src/changes/changes.xml index 11f89c4fb..c5516d5f2 100644 --- a/src/changes/changes.xml +++ b/src/changes/changes.xml @@ -95,6 +95,7 @@ The type attribute can be add,update,fix,remove. Add org.apache.commons.lang3.arch.Processor.Arch.getLabel(). Add IS_JAVA_14 and IS_JAVA_15 to org.apache.commons.lang3.SystemUtils. ObjectUtils: Get first non-null supplier value. + Added the Streams class, and Functions.stream() as an accessor thereof. diff --git a/src/main/java/org/apache/commons/lang3/Functions.java b/src/main/java/org/apache/commons/lang3/Functions.java index 2d0ca06b7..ef9c45d90 100644 --- a/src/main/java/org/apache/commons/lang3/Functions.java +++ b/src/main/java/org/apache/commons/lang3/Functions.java @@ -19,6 +19,7 @@ package org.apache.commons.lang3; import java.io.IOException; import java.io.UncheckedIOException; import java.lang.reflect.UndeclaredThrowableException; +import java.util.Collection; import java.util.Objects; import java.util.concurrent.Callable; import java.util.function.BiConsumer; @@ -28,6 +29,9 @@ import java.util.function.Consumer; import java.util.function.Function; import java.util.function.Predicate; import java.util.function.Supplier; +import java.util.stream.Stream; + +import org.apache.commons.lang3.Streams.FailableStream; /** This class provides utility functions, and classes for working with the @@ -400,6 +404,39 @@ public class Functions { } } + /** + * Converts the given stream into a {@link FailableStream}. The + * {@link FailableStream} consists of the same elements, than the + * input stream. However, failable lambdas, like + * {@link FailablePredicate}, {@link FailableFunction}, and + * {@link FailableConsumer} may be applied, rather than + * {@link Predicate}, {@link Function}, {@link Consumer}, etc. + * @param pStream The stream, which is being converted into a + * {@link FailableStream}. + * @param The streams element type. + * @return The created {@link FailableStream}. + */ + public static FailableStream stream(Stream pStream) { + return new FailableStream(pStream); + } + + /** + * Converts the given collection into a {@link FailableStream}. + * The {@link FailableStream} consists of the collections + * elements. Shortcut for + * 
+     *   Functions.stream(pCollection.stream());
+     *
+ * @param pCollection The collection, which is being converted into a + * {@link FailableStream}. + * @param The collections element type. (In turn, the result + * streams element type.) + * @return The created {@link FailableStream}. + */ + public static FailableStream stream(Collection pCollection) { + return new FailableStream(pCollection.stream()); + } + /** * A simple try-with-resources implementation, that can be used, if your diff --git a/src/main/java/org/apache/commons/lang3/Streams.java b/src/main/java/org/apache/commons/lang3/Streams.java new file mode 100644 index 000000000..a0f32afec --- /dev/null +++ b/src/main/java/org/apache/commons/lang3/Streams.java @@ -0,0 +1,380 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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.apache.commons.lang3; + +import java.util.function.BiConsumer; +import java.util.function.BinaryOperator; +import java.util.function.Consumer; +import java.util.function.Function; +import java.util.function.Predicate; +import java.util.function.Supplier; +import java.util.stream.Collector; +import java.util.stream.Collectors; +import java.util.stream.Stream; + +import org.apache.commons.lang3.Functions.FailableConsumer; +import org.apache.commons.lang3.Functions.FailableFunction; +import org.apache.commons.lang3.Functions.FailablePredicate; + +/** + * This class provides utility functions, and classes for working with the + * java.util.stream package, or more generally, with Java 8 lambdas. More + * specifically, it attempts to address the fact that lambdas are supposed + * not to throw Exceptions, at least not checked Exceptions, aka instances + * of {@link Exception}. This enforces the use of constructs like + * 
+ *     Consumer<java.lang.reflect.Method> consumer = (m) -> {
+ *         try {
+ *             m.invoke(o, args);
+ *         } catch (Throwable t) {
+ *             throw Functions.rethrow(t);
+ *         }
+ *    };
+ *    stream.forEach(consumer);
+ *
+ * Using a {@link FailableStream}, this can be rewritten as follows: + * 
+ *     ObjectStreams.failable(stream).forEach((m) -> m.invoke(o, args));
+ *
+ * Obviously, the second version is much more concise and the spirit of + * Lambda expressions is met better than in the first version. + * @see Stream + * @see Functions + */ +public class Streams { + /** A reduced, and simplified version of a {@link Stream} with + * failable method signatures. + * @param The streams element type. + */ + public static class FailableStream { + private Stream stream; + private boolean terminated; + + public FailableStream(Stream pStream) { + stream = pStream; + } + + protected void assertNotTerminated() { + if (terminated) { + throw new IllegalStateException("This stream is already terminated."); + } + } + + protected void makeTerminated() { + assertNotTerminated(); + terminated = true; + } + + /** + * Returns a FailableStream consisting of the elements of this stream that match + * the given FailablePredicate. + * + *

This is an intermediate operation. + * + * @param pPredicate a non-interfering, stateless predicate to apply to each + * element to determine if it should be included. + * @return the new stream + */ + public FailableStream filter(FailablePredicate pPredicate){ + assertNotTerminated(); + stream = stream.filter(Functions.asPredicate(pPredicate)); + return this; + } + + /** + * Performs an action for each element of this stream. + * + *

This is a terminal operation. + * + *

The behavior of this operation is explicitly nondeterministic. + * For parallel stream pipelines, this operation does not + * guarantee to respect the encounter order of the stream, as doing so + * would sacrifice the benefit of parallelism. For any given element, the + * action may be performed at whatever time and in whatever thread the + * library chooses. If the action accesses shared state, it is + * responsible for providing the required synchronization. + * + * @param pAction a non-interfering action to perform on the elements + */ + public void forEach(FailableConsumer pAction) { + makeTerminated(); + stream().forEach(Functions.asConsumer(pAction)); + } + + /** + * Performs a mutable reduction operation on the elements of this stream using a + * {@code Collector}. A {@code Collector} + * encapsulates the functions used as arguments to + * {@link #collect(Supplier, BiConsumer, BiConsumer)}, allowing for reuse of + * collection strategies and composition of collect operations such as + * multiple-level grouping or partitioning. + * + *

If the underlying stream is parallel, and the {@code Collector} + * is concurrent, and either the stream is unordered or the collector is + * unordered, then a concurrent reduction will be performed + * (see {@link Collector} for details on concurrent reduction.) + * + *

This is a terminal operation. + * + *

When executed in parallel, multiple intermediate results may be + * instantiated, populated, and merged so as to maintain isolation of + * mutable data structures. Therefore, even when executed in parallel + * with non-thread-safe data structures (such as {@code ArrayList}), no + * additional synchronization is needed for a parallel reduction. + * + * \@apiNote + * The following will accumulate strings into an ArrayList: + * 

{@code
+	     *     List asList = stringStream.collect(Collectors.toList());
+	     * }
+ * + *

The following will classify {@code Person} objects by city: + * 

{@code
+	     *     Map> peopleByCity
+	     *         = personStream.collect(Collectors.groupingBy(Person::getCity));
+	     * }
+ * + *

The following will classify {@code Person} objects by state and city, + * cascading two {@code Collector}s together: + * 

{@code
+	     *     Map>> peopleByStateAndCity
+	     *         = personStream.collect(Collectors.groupingBy(Person::getState,
+	     *                                                      Collectors.groupingBy(Person::getCity)));
+	     * }
+ * + * @param the type of the result + * @param the intermediate accumulation type of the {@code Collector} + * @param pCollector the {@code Collector} describing the reduction + * @return the result of the reduction + * @see #collect(Supplier, BiConsumer, BiConsumer) + * @see Collectors + */ + public R collect(Collector pCollector) { + makeTerminated(); + return stream().collect(pCollector); + } + + /** + * Performs a mutable reduction operation on the elements of this FailableStream. + * A mutable reduction is one in which the reduced value is a mutable result + * container, such as an {@code ArrayList}, and elements are incorporated by updating + * the state of the result rather than by replacing the result. This produces a result equivalent to: + * 
{@code
+	     *     R result = supplier.get();
+	     *     for (T element : this stream)
+	     *         accumulator.accept(result, element);
+	     *     return result;
+	     * }
+ * + *

Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations + * can be parallelized without requiring additional synchronization. + * + *

This is a terminal operation. + * + * \@apiNote There are many existing classes in the JDK whose signatures are + * well-suited for use with method references as arguments to {@code collect()}. + * For example, the following will accumulate strings into an {@code ArrayList}: + * 

{@code
+	     *     List asList = stringStream.collect(ArrayList::new, ArrayList::add,
+	     *                                                ArrayList::addAll);
+	     * }
+ * + *

The following will take a stream of strings and concatenates them into a + * single string: + * 

{@code
+	     *     String concat = stringStream.collect(StringBuilder::new, StringBuilder::append,
+	     *                                          StringBuilder::append)
+	     *                                 .toString();
+	     * }
+ * + * @param type of the result + * @param Type of the accumulator. + * @param pSupplier a function that creates a new result container. For a + * parallel execution, this function may be called + * multiple times and must return a fresh value each time. + * @param pAccumulator An associative, non-interfering, stateless function for + * incorporating an additional element into a result + * @param pCombiner An associative, non-interfering, stateless + * function for combining two values, which must be compatible with the + * accumulator function + * @return The result of the reduction + */ + public R collect(Supplier pSupplier, BiConsumer pAccumulator, BiConsumer pCombiner) { + makeTerminated(); + return stream().collect(pSupplier, pAccumulator, pCombiner); + } + + /** + * Performs a reduction on the elements of this stream, using the provided + * identity value and an associative accumulation function, and returns + * the reduced value. This is equivalent to: + * 
{@code
+	     *     T result = identity;
+	     *     for (T element : this stream)
+	     *         result = accumulator.apply(result, element)
+	     *     return result;
+	     * }
+ * + * but is not constrained to execute sequentially. + * + *

The {@code identity} value must be an identity for the accumulator + * function. This means that for all {@code t}, + * {@code accumulator.apply(identity, t)} is equal to {@code t}. + * The {@code accumulator} function must be an associative function. + * + *

This is a terminal operation. + * + * \@apiNote Sum, min, max, average, and string concatenation are all special + * cases of reduction. Summing a stream of numbers can be expressed as: + * + * 

{@code
+	     *     Integer sum = integers.reduce(0, (a, b) -> a+b);
+	     * }
+ * + * or: + * + * 
{@code
+	     *     Integer sum = integers.reduce(0, Integer::sum);
+	     * }
+ * + *

While this may seem a more roundabout way to perform an aggregation + * compared to simply mutating a running total in a loop, reduction + * operations parallelize more gracefully, without needing additional + * synchronization and with greatly reduced risk of data races. + * + * @param pIdentity the identity value for the accumulating function + * @param pAccumulator an associative, non-interfering, stateless + * function for combining two values + * @return the result of the reduction + */ + public O reduce(O pIdentity, BinaryOperator pAccumulator) { + makeTerminated(); + return stream().reduce(pIdentity, pAccumulator); + } + + /** + * Returns a stream consisting of the results of applying the given + * function to the elements of this stream. + * + *

This is an intermediate operation. + * + * @param The element type of the new stream + * @param pMapper A non-interfering, stateless function to apply to each element + * @return the new stream + */ + public FailableStream map(FailableFunction pMapper) { + assertNotTerminated(); + return new FailableStream(stream.map(Functions.asFunction(pMapper))); + } + + /** + * Converts the FailableStream into an equivalent stream. + * @return A stream, which will return the same elements, which this FailableStream would return. + */ + public Stream stream() { + return stream; + } + + /** + * Returns whether all elements of this stream match the provided predicate. + * May not evaluate the predicate on all elements if not necessary for + * determining the result. If the stream is empty then {@code true} is + * returned and the predicate is not evaluated. + * + *

This is a short-circuiting terminal operation. + * + * \@apiNote + * This method evaluates the universal quantification of the + * predicate over the elements of the stream (for all x P(x)). If the + * stream is empty, the quantification is said to be vacuously + * satisfied and is always {@code true} (regardless of P(x)). + * + * @param pPredicate A non-interfering, stateless predicate to apply to + * elements of this stream + * @return {@code true} If either all elements of the stream match the + * provided predicate or the stream is empty, otherwise {@code false}. + */ + public boolean allMatch(FailablePredicate pPredicate) { + assertNotTerminated(); + return stream().allMatch(Functions.asPredicate(pPredicate)); + } + + /** + * Returns whether any elements of this stream match the provided + * predicate. May not evaluate the predicate on all elements if not + * necessary for determining the result. If the stream is empty then + * {@code false} is returned and the predicate is not evaluated. + * + *

This is a short-circuiting terminal operation. + * + * \@apiNote + * This method evaluates the existential quantification of the + * predicate over the elements of the stream (for some x P(x)). + * + * @param pPredicate A non-interfering, stateless predicate to apply to + * elements of this stream + * @return {@code true} if any elements of the stream match the provided + * predicate, otherwise {@code false} + */ + public boolean anyMatch(FailablePredicate pPredicate) { + assertNotTerminated(); + return stream().anyMatch(Functions.asPredicate(pPredicate)); + } + } + + /** + * Converts the given {@link Stream stream} into a {@link FailableStream}. + * This is basically a simplified, reduced version of the {@link Stream} + * class, with the same underlying element stream, except that failable + * objects, like {@link FailablePredicate}, {@link FailableFunction}, or + * {@link FailableConsumer} may be applied, instead of + * {@link Predicate}, {@link Function}, or {@link Consumer}. The idea is + * to rewrite a code snippet like this: + * 

+	 *     final List<O> list;
+	 *     final Method m;
+	 *     final Function<O,String> mapper = (o) -> {
+	 *         try {
+	 *             return (String) m.invoke(o);
+	 *         } catch (Throwable t) {
+	 *             throw Functions.rethrow(t);
+	 *         }
+	 *     };
+	 *     final List<String> strList = list.stream()
+	 *         .map(mapper).collect(Collectors.toList());
+	 *
+ * as follows: + * 
+     *     final List<O> list;
+     *     final Method m;
+     *     final List<String> strList = Functions.stream(list.stream())
+     *         .map((o) -> (String) m.invoke(o)).collect(Collectors.toList());
+     *
+ * While the second version may not be quite as + * efficient (because it depends on the creation of additional, + * intermediate objects, of type FailableStream), it is much more + * concise, and readable, and meets the spirit of Lambdas better + * than the first version. + * @param The streams element type. + * @param pStream The stream, which is being converted. + * @return The {@link FailableStream}, which has been created by + * converting the stream. + */ + public static FailableStream stream(Stream pStream) { + return new FailableStream(pStream); + } +} diff --git a/src/test/java/org/apache/commons/lang3/StreamsTest.java b/src/test/java/org/apache/commons/lang3/StreamsTest.java new file mode 100644 index 000000000..9ad8e7810 --- /dev/null +++ b/src/test/java/org/apache/commons/lang3/StreamsTest.java @@ -0,0 +1,176 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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.apache.commons.lang3; + +import static org.junit.jupiter.api.Assertions.*; + +import java.lang.reflect.UndeclaredThrowableException; +import java.util.ArrayList; +import java.util.Arrays; +import java.util.List; +import java.util.stream.Collectors; + +import org.apache.commons.lang3.Functions.FailableConsumer; +import org.apache.commons.lang3.Functions.FailablePredicate; +import org.junit.jupiter.api.Test; +import org.xml.sax.SAXException; + +class StreamsTest { + @Test + void testSimpleStreamMap() { + final List input = Arrays.asList("1", "2", "3", "4", "5", "6"); + final List output = Functions.stream(input).map((s) -> Integer.valueOf(s)).collect(Collectors.toList()); + assertEquals(6, output.size()); + for (int i = 0; i < 6; i++) { + assertEquals(i+1, output.get(i).intValue()); + } + } + + @Test + void testSimpleStreamMapFailing() { + final List input = Arrays.asList("1", "2", "3", "4 ", "5", "6"); + try { + Functions.stream(input).map((s) -> Integer.valueOf(s)).collect(Collectors.toList()); + fail("Expected Exception"); + } catch (NumberFormatException nfe) { + assertEquals("For input string: \"4 \"", nfe.getMessage()); + } + } + + @Test + void testSimpleStreamForEach() { + final List input = Arrays.asList("1", "2", "3", "4", "5", "6"); + final List output = new ArrayList<>(); + Functions.stream(input).forEach((s) -> output.add(Integer.valueOf(s))); + assertEquals(6, output.size()); + for (int i = 0; i < 6; i++) { + assertEquals(i+1, output.get(i).intValue()); + } + } + + protected FailableConsumer asIntConsumer(T pThrowable) { + return (s) -> { + final Integer i = Integer.valueOf(s); + if (i.intValue() == 4) { + throw pThrowable; + } + }; + } + + @Test + void testSimpleStreamForEachFailing() { + final List input = Arrays.asList("1", "2", "3", "4", "5", "6"); + final List output = new ArrayList<>(); + final IllegalArgumentException ise = new IllegalArgumentException("Invalid argument: 4"); + try { + Functions.stream(input).forEach(asIntConsumer(ise)); + fail("Expected Exception"); + } catch (IllegalArgumentException e) { + assertSame(ise, e); + } + output.clear(); + final OutOfMemoryError oome = new OutOfMemoryError(); + try { + Functions.stream(input).forEach(asIntConsumer(oome)); + fail("Expected Exception"); + } catch (Throwable t) { + assertSame(oome, t); + } + output.clear(); + final SAXException se = new SAXException(); + try { + Functions.stream(input).forEach(asIntConsumer(se)); + fail("Expected Exception"); + } catch (UndeclaredThrowableException ute) { + assertSame(se, ute.getCause()); + } + } + + @Test + void testSimpleStreamFilter() { + final List input = Arrays.asList("1", "2", "3", "4", "5", "6"); + final List output = Functions.stream(input) + .map((s) -> Integer.valueOf(s)) + .filter((i) -> { return i.intValue() %2 == 0;}) + .collect(Collectors.toList()); + assertEvenNumbers(output); + } + + private void assertEvenNumbers(final List output) { + assertEquals(3, output.size()); + for (int i = 0; i < 3; i++) { + assertEquals((i+1)*2, output.get(i).intValue()); + } + } + + protected FailablePredicate asIntPredicate(T pThrowable) { + return (i) -> { + if (i.intValue() == 5) { + if (pThrowable != null) { + throw pThrowable; + } + } + return i%2==0; + }; + } + + @Test + void testSimpleStreamFilterFailing() { + final List input = Arrays.asList("1", "2", "3", "4", "5", "6"); + final List output = Functions.stream(input) + .map((s) -> Integer.valueOf(s)) + .filter(asIntPredicate(null)) + .collect(Collectors.toList()); + assertEvenNumbers(output); + + output.clear(); + final IllegalArgumentException iae = new IllegalArgumentException("Invalid argument: " + 5); + try { + Functions.stream(input) + .map((s) -> Integer.valueOf(s)) + .filter(asIntPredicate(iae)) + .collect(Collectors.toList()); + fail("Expected Exception"); + } catch (IllegalArgumentException e) { + assertSame(iae, e); + } + + output.clear(); + final OutOfMemoryError oome = new OutOfMemoryError(); + try { + Functions.stream(input) + .map((s) -> Integer.valueOf(s)) + .filter(asIntPredicate(oome)) + .collect(Collectors.toList()); + fail("Expected Exception"); + } catch (Throwable t) { + assertSame(oome, t); + } + + output.clear(); + final SAXException se = new SAXException(); + try { + Functions.stream(input) + .map((s) -> Integer.valueOf(s)) + .filter(asIntPredicate(se)) + .collect(Collectors.toList()); + fail("Expected Exception"); + } catch (UndeclaredThrowableException t) { + assertSame(se, t.getCause()); + } + } +}