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- Added the Streams class. 

- Added Functions.stream() as an accessor method.
This commit is contained in:
Jochen Wiedmann 2020-01-26 22:57:13 +01:00
parent bfc88d23cb
commit 2ea44b2ada
4 changed files with 594 additions and 0 deletions
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1
src/changes/changes.xml
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@ -95,6 +95,7 @@ The <action> type attribute can be add,update,fix,remove.
<action issue="LANG-1510" type="add" dev="ggregory" due-to="Gary Gregory">Add org.apache.commons.lang3.arch.Processor.Arch.getLabel().</action>
<action issue="LANG-1512" type="add" dev="ggregory" due-to="Gary Gregory">Add IS_JAVA_14 and IS_JAVA_15 to org.apache.commons.lang3.SystemUtils.</action>
<action issue="LANG-1513" type="add" dev="ggregory" due-to="Bernhard Bonigl, Gary Gregory">ObjectUtils: Get first non-null supplier value.</action>
<action type="add" dev="jochen">Added the Streams class, and Functions.stream() as an accessor thereof.</action>
</release>
<release version="3.9" date="2019-04-09" description="New features and bug fixes. Requires Java 8, supports Java 9, 10, 11.">

37
src/main/java/org/apache/commons/lang3/Functions.java
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@ -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 <O> The streams element type.
* @return The created {@link FailableStream}.
*/
public static <O> FailableStream<O> stream(Stream<O> pStream) {
return new FailableStream<O>(pStream);
}
/**
* Converts the given collection into a {@link FailableStream}.
* The {@link FailableStream} consists of the collections
* elements. Shortcut for
* <pre>
* Functions.stream(pCollection.stream());
* </pre>
* @param pCollection The collection, which is being converted into a
* {@link FailableStream}.
* @param <O> The collections element type. (In turn, the result
* streams element type.)
* @return The created {@link FailableStream}.
*/
public static <O> FailableStream<O> stream(Collection<O> pCollection) {
return new FailableStream<O>(pCollection.stream());
}
/**
* A simple try-with-resources implementation, that can be used, if your

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src/main/java/org/apache/commons/lang3/Streams.java Normal file
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@ -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
* <pre>
* Consumer&lt;java.lang.reflect.Method&gt; consumer = (m) -&gt; {
* try {
* m.invoke(o, args);
* } catch (Throwable t) {
* throw Functions.rethrow(t);
* }
* };
* stream.forEach(consumer);
* </pre>
* Using a {@link FailableStream}, this can be rewritten as follows:
* <pre>
* ObjectStreams.failable(stream).forEach((m) -&gt; m.invoke(o, args));
* </pre>
* 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 <O> The streams element type.
*/
public static class FailableStream<O extends Object> {
private Stream<O> stream;
private boolean terminated;
public FailableStream(Stream<O> 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.
*
* <p>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<O> filter(FailablePredicate<O,?> pPredicate){
assertNotTerminated();
stream = stream.filter(Functions.asPredicate(pPredicate));
return this;
}
/**
* Performs an action for each element of this stream.
*
* <p>This is a terminal operation.
*
* <p>The behavior of this operation is explicitly nondeterministic.
* For parallel stream pipelines, this operation does <em>not</em>
* 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<O,?> 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.
*
* <p>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.)
*
* <p>This is a terminal operation.
*
* <p>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:
* <pre>{@code
* List<String> asList = stringStream.collect(Collectors.toList());
* }</pre>
*
* <p>The following will classify {@code Person} objects by city:
* <pre>{@code
* Map<String, List<Person>> peopleByCity
* = personStream.collect(Collectors.groupingBy(Person::getCity));
* }</pre>
*
* <p>The following will classify {@code Person} objects by state and city,
* cascading two {@code Collector}s together:
* <pre>{@code
* Map<String, Map<String, List<Person>>> peopleByStateAndCity
* = personStream.collect(Collectors.groupingBy(Person::getState,
* Collectors.groupingBy(Person::getCity)));
* }</pre>
*
* @param <R> the type of the result
* @param <A> 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 <A,R> R collect(Collector<? super O,A,R> 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:
* <pre>{@code
* R result = supplier.get();
* for (T element : this stream)
* accumulator.accept(result, element);
* return result;
* }</pre>
*
* <p>Like {@link #reduce(Object, BinaryOperator)}, {@code collect} operations
* can be parallelized without requiring additional synchronization.
*
* <p>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}:
* <pre>{@code
* List<String> asList = stringStream.collect(ArrayList::new, ArrayList::add,
* ArrayList::addAll);
* }</pre>
*
* <p>The following will take a stream of strings and concatenates them into a
* single string:
* <pre>{@code
* String concat = stringStream.collect(StringBuilder::new, StringBuilder::append,
* StringBuilder::append)
* .toString();
* }</pre>
*
* @param <R> type of the result
* @param <A> 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 <A,R> R collect(Supplier<R> pSupplier, BiConsumer<R,? super O> pAccumulator, BiConsumer<R,R> 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:
* <pre>{@code
* T result = identity;
* for (T element : this stream)
* result = accumulator.apply(result, element)
* return result;
* }</pre>
*
* but is not constrained to execute sequentially.
*
* <p>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.
*
* <p>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:
*
* <pre>{@code
* Integer sum = integers.reduce(0, (a, b) -> a+b);
* }</pre>
*
* or:
*
* <pre>{@code
* Integer sum = integers.reduce(0, Integer::sum);
* }</pre>
*
* <p>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<O> 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.
*
* <p>This is an intermediate operation.
*
* @param <R> The element type of the new stream
* @param pMapper A non-interfering, stateless function to apply to each element
* @return the new stream
*/
public <R> FailableStream<R> map(FailableFunction<O,R,?> pMapper) {
assertNotTerminated();
return new FailableStream<R>(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<O> 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.
*
* <p>This is a short-circuiting terminal operation.
*
* \@apiNote
* This method evaluates the <em>universal quantification</em> 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 <em>vacuously
* satisfied</em> 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<O,?> 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.
*
* <p>This is a short-circuiting terminal operation.
*
* \@apiNote
* This method evaluates the <em>existential quantification</em> 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<O,?> 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:
* <pre>
* final List&lt;O&gt; list;
* final Method m;
* final Function&lt;O,String&gt; mapper = (o) -&gt; {
* try {
* return (String) m.invoke(o);
* } catch (Throwable t) {
* throw Functions.rethrow(t);
* }
* };
* final List&lt;String&gt; strList = list.stream()
* .map(mapper).collect(Collectors.toList());
* </pre>
* as follows:
* <pre>
* final List&lt;O&gt; list;
* final Method m;
* final List&lt;String&gt; strList = Functions.stream(list.stream())
* .map((o) -&gt; (String) m.invoke(o)).collect(Collectors.toList());
* </pre>
* While the second version may not be <em>quite</em> 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 <O> 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 <O> FailableStream<O> stream(Stream<O> pStream) {
return new FailableStream<O>(pStream);
}
}

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src/test/java/org/apache/commons/lang3/StreamsTest.java Normal file
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@ -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<String> input = Arrays.asList("1", "2", "3", "4", "5", "6");
final List<Integer> 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<String> 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<String> input = Arrays.asList("1", "2", "3", "4", "5", "6");
final List<Integer> 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 <T extends Throwable> FailableConsumer<String,T> asIntConsumer(T pThrowable) {
return (s) -> {
final Integer i = Integer.valueOf(s);
if (i.intValue() == 4) {
throw pThrowable;
}
};
}
@Test
void testSimpleStreamForEachFailing() {
final List<String> input = Arrays.asList("1", "2", "3", "4", "5", "6");
final List<Integer> 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<String> input = Arrays.asList("1", "2", "3", "4", "5", "6");
final List<Integer> 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<Integer> output) {
assertEquals(3, output.size());
for (int i = 0; i < 3; i++) {
assertEquals((i+1)*2, output.get(i).intValue());
}
}
protected <T extends Throwable> FailablePredicate<Integer,T> asIntPredicate(T pThrowable) {
return (i) -> {
if (i.intValue() == 5) {
if (pThrowable != null) {
throw pThrowable;
}
}
return i%2==0;
};
}
@Test
void testSimpleStreamFilterFailing() {
final List<String> input = Arrays.asList("1", "2", "3", "4", "5", "6");
final List<Integer> 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());
}
}
}