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Java 5065 (#11126) 

* Commit source code to branch

* BAEL-5065 improvement of groupBy with complex key
This commit is contained in:
mbarriola 2021-08-16 17:43:53 -04:00 committed by GitHub
parent be7893bc1c
commit 640f0d6dde
5 changed files with 383 additions and 40 deletions
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85
core-java-modules/core-java-16/pom.xml
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@ -1,48 +1,53 @@
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<artifactId>core-java-16</artifactId>
<version>0.1.0-SNAPSHOT</version>
<name>core-java-16</name>
<packaging>jar</packaging>
<url>http://maven.apache.org</url>
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<artifactId>core-java-16</artifactId>
<version>0.1.0-SNAPSHOT</version>
<name>core-java-16</name>
<packaging>jar</packaging>
<url>http://maven.apache.org</url>
<parent>
<groupId>com.baeldung</groupId>
<artifactId>parent-modules</artifactId>
<version>1.0.0-SNAPSHOT</version>
<relativePath>../../</relativePath>
</parent>
<parent>
<groupId>com.baeldung</groupId>
<artifactId>parent-modules</artifactId>
<version>1.0.0-SNAPSHOT</version>
<relativePath>../../</relativePath>
</parent>
<dependencies>
<dependency>
<groupId>org.assertj</groupId>
<artifactId>assertj-core</artifactId>
<version>${assertj.version}</version>
<scope>test</scope>
</dependency>
</dependencies>
<dependencies>
<dependency>
<groupId>org.assertj</groupId>
<artifactId>assertj-core</artifactId>
<version>${assertj.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.12.0</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>${maven-compiler-plugin.version}</version>
<configuration>
<source>${maven.compiler.source.version}</source>
<target>${maven.compiler.target.version}</target>
</configuration>
</plugin>
</plugins>
</build>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>${maven-compiler-plugin.version}</version>
<configuration>
<source>${maven.compiler.source.version}</source>
<target>${maven.compiler.target.version}</target>
</configuration>
</plugin>
</plugins>
</build>
<properties>
<maven.compiler.source.version>16</maven.compiler.source.version>
<maven.compiler.target.version>16</maven.compiler.target.version>
<assertj.version>3.6.1</assertj.version>
</properties>
<properties>
<maven.compiler.source.version>16</maven.compiler.source.version>
<maven.compiler.target.version>16</maven.compiler.target.version>
<assertj.version>3.6.1</assertj.version>
</properties>
</project>

38
core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/groupingby/BlogPost.java Normal file
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package com.baeldung.java_16_features.groupingby;
public class BlogPost {
private String title;
private String author;
private BlogPostType type;
private int likes;
record AuthPostTypesLikes(String author, BlogPostType type, int likes) {};
public BlogPost(String title, String author, BlogPostType type, int likes) {
this.title = title;
this.author = author;
this.type = type;
this.likes = likes;
}
public String getTitle() {
return title;
}
public String getAuthor() {
return author;
}
public BlogPostType getType() {
return type;
}
public int getLikes() {
return likes;
}
@Override
public String toString() {
return "BlogPost{" + "title='" + title + '\'' + ", type=" + type + ", likes=" + likes + '}';
}
}

5
core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/groupingby/BlogPostType.java Normal file
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package com.baeldung.java_16_features.groupingby;
public enum BlogPostType {
NEWS, REVIEW, GUIDE
}

41
core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/groupingby/Tuple.java Normal file
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package com.baeldung.java_16_features.groupingby;
import java.util.Objects;
public class Tuple {
private final BlogPostType type;
private final String author;
public Tuple(BlogPostType type, String author) {
this.type = type;
this.author = author;
}
public BlogPostType getType() {
return type;
}
public String getAuthor() {
return author;
}
@Override
public boolean equals(Object o) {
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
Tuple tuple = (Tuple) o;
return type == tuple.type && author.equals(tuple.author);
}
@Override
public int hashCode() {
return Objects.hash(type, author);
}
@Override
public String toString() {
return "Tuple{" + "type=" + type + ", author='" + author + '\'' + '}';
}
}

254
core-java-modules/core-java-16/src/test/java/com/baeldung/java_16_features/groupingby/JavaGroupingByCollectorUnitTest.java Normal file
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package com.baeldung.java_16_features.groupingby;
import static java.util.Comparator.comparingInt;
import static java.util.stream.Collectors.averagingInt;
import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.groupingByConcurrent;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.mapping;
import static java.util.stream.Collectors.maxBy;
import static java.util.stream.Collectors.summarizingInt;
import static java.util.stream.Collectors.summingInt;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toSet;
import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertTrue;
import java.util.Arrays;
import java.util.EnumMap;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import org.apache.commons.lang3.tuple.ImmutablePair;
import org.apache.commons.lang3.tuple.Pair;
import org.junit.jupiter.api.Test;
public class JavaGroupingByCollectorUnitTest {
private static final List<BlogPost> posts = Arrays.asList(new BlogPost("News item 1", "Author 1", BlogPostType.NEWS, 15), new BlogPost("Tech review 1", "Author 2", BlogPostType.REVIEW, 5),
new BlogPost("Programming guide", "Author 1", BlogPostType.GUIDE, 20), new BlogPost("News item 2", "Author 2", BlogPostType.NEWS, 35), new BlogPost("Tech review 2", "Author 1", BlogPostType.REVIEW, 15));
@Test
public void givenAListOfPosts_whenGroupedByType_thenGetAMapBetweenTypeAndPosts() {
Map<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
.collect(groupingBy(BlogPost::getType));
assertEquals(2, postsPerType.get(BlogPostType.NEWS)
.size());
assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
.size());
assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
.size());
}
@Test
public void givenAListOfPosts_whenGroupedByTypeAndTheirTitlesAreJoinedInAString_thenGetAMapBetweenTypeAndCsvTitles() {
Map<BlogPostType, String> postsPerType = posts.stream()
.collect(groupingBy(BlogPost::getType, mapping(BlogPost::getTitle, joining(", ", "Post titles: [", "]"))));
assertEquals("Post titles: [News item 1, News item 2]", postsPerType.get(BlogPostType.NEWS));
assertEquals("Post titles: [Programming guide]", postsPerType.get(BlogPostType.GUIDE));
assertEquals("Post titles: [Tech review 1, Tech review 2]", postsPerType.get(BlogPostType.REVIEW));
}
@Test
public void givenAListOfPosts_whenGroupedByTypeAndSumTheLikes_thenGetAMapBetweenTypeAndPostLikes() {
Map<BlogPostType, Integer> likesPerType = posts.stream()
.collect(groupingBy(BlogPost::getType, summingInt(BlogPost::getLikes)));
assertEquals(50, likesPerType.get(BlogPostType.NEWS)
.intValue());
assertEquals(20, likesPerType.get(BlogPostType.REVIEW)
.intValue());
assertEquals(20, likesPerType.get(BlogPostType.GUIDE)
.intValue());
}
@Test
public void givenAListOfPosts_whenGroupedByTypeInAnEnumMap_thenGetAnEnumMapBetweenTypeAndPosts() {
EnumMap<BlogPostType, List<BlogPost>> postsPerType = posts.stream()
.collect(groupingBy(BlogPost::getType, () -> new EnumMap<>(BlogPostType.class), toList()));
assertEquals(2, postsPerType.get(BlogPostType.NEWS)
.size());
assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
.size());
assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
.size());
}
@Test
public void givenAListOfPosts_whenGroupedByTypeInSets_thenGetAMapBetweenTypesAndSetsOfPosts() {
Map<BlogPostType, Set<BlogPost>> postsPerType = posts.stream()
.collect(groupingBy(BlogPost::getType, toSet()));
assertEquals(2, postsPerType.get(BlogPostType.NEWS)
.size());
assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
.size());
assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
.size());
}
@Test
public void givenAListOfPosts_whenGroupedByTypeConcurrently_thenGetAMapBetweenTypeAndPosts() {
ConcurrentMap<BlogPostType, List<BlogPost>> postsPerType = posts.parallelStream()
.collect(groupingByConcurrent(BlogPost::getType));
assertEquals(2, postsPerType.get(BlogPostType.NEWS)
.size());
assertEquals(1, postsPerType.get(BlogPostType.GUIDE)
.size());
assertEquals(2, postsPerType.get(BlogPostType.REVIEW)
.size());
}
@Test
public void givenAListOfPosts_whenGroupedByTypeAndAveragingLikes_thenGetAMapBetweenTypeAndAverageNumberOfLikes() {
Map<BlogPostType, Double> averageLikesPerType = posts.stream()
.collect(groupingBy(BlogPost::getType, averagingInt(BlogPost::getLikes)));
assertEquals(25, averageLikesPerType.get(BlogPostType.NEWS)
.intValue());
assertEquals(20, averageLikesPerType.get(BlogPostType.GUIDE)
.intValue());
assertEquals(10, averageLikesPerType.get(BlogPostType.REVIEW)
.intValue());
}
@Test
public void givenAListOfPosts_whenGroupedByTypeAndCounted_thenGetAMapBetweenTypeAndNumberOfPosts() {
Map<BlogPostType, Long> numberOfPostsPerType = posts.stream()
.collect(groupingBy(BlogPost::getType, counting()));
assertEquals(2, numberOfPostsPerType.get(BlogPostType.NEWS)
.intValue());
assertEquals(1, numberOfPostsPerType.get(BlogPostType.GUIDE)
.intValue());
assertEquals(2, numberOfPostsPerType.get(BlogPostType.REVIEW)
.intValue());
}
@Test
public void givenAListOfPosts_whenGroupedByTypeAndMaxingLikes_thenGetAMapBetweenTypeAndMaximumNumberOfLikes() {
Map<BlogPostType, Optional<BlogPost>> maxLikesPerPostType = posts.stream()
.collect(groupingBy(BlogPost::getType, maxBy(comparingInt(BlogPost::getLikes))));
assertTrue(maxLikesPerPostType.get(BlogPostType.NEWS)
.isPresent());
assertEquals(35, maxLikesPerPostType.get(BlogPostType.NEWS)
.get()
.getLikes());
assertTrue(maxLikesPerPostType.get(BlogPostType.GUIDE)
.isPresent());
assertEquals(20, maxLikesPerPostType.get(BlogPostType.GUIDE)
.get()
.getLikes());
assertTrue(maxLikesPerPostType.get(BlogPostType.REVIEW)
.isPresent());
assertEquals(15, maxLikesPerPostType.get(BlogPostType.REVIEW)
.get()
.getLikes());
}
@Test
public void givenAListOfPosts_whenGroupedByAuthorAndThenByType_thenGetAMapBetweenAuthorAndMapsBetweenTypeAndBlogPosts() {
Map<String, Map<BlogPostType, List<BlogPost>>> map = posts.stream()
.collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));
assertEquals(1, map.get("Author 1")
.get(BlogPostType.NEWS)
.size());
assertEquals(1, map.get("Author 1")
.get(BlogPostType.GUIDE)
.size());
assertEquals(1, map.get("Author 1")
.get(BlogPostType.REVIEW)
.size());
assertEquals(1, map.get("Author 2")
.get(BlogPostType.NEWS)
.size());
assertEquals(1, map.get("Author 2")
.get(BlogPostType.REVIEW)
.size());
assertNull(map.get("Author 2")
.get(BlogPostType.GUIDE));
}
@Test
public void givenAListOfPosts_whenGroupedByTypeAndSummarizingLikes_thenGetAMapBetweenTypeAndSummary() {
Map<BlogPostType, IntSummaryStatistics> likeStatisticsPerType = posts.stream()
.collect(groupingBy(BlogPost::getType, summarizingInt(BlogPost::getLikes)));
IntSummaryStatistics newsLikeStatistics = likeStatisticsPerType.get(BlogPostType.NEWS);
assertEquals(2, newsLikeStatistics.getCount());
assertEquals(50, newsLikeStatistics.getSum());
assertEquals(25.0, newsLikeStatistics.getAverage(), 0.001);
assertEquals(35, newsLikeStatistics.getMax());
assertEquals(15, newsLikeStatistics.getMin());
}
@Test
public void givenAListOfPosts_whenGroupedByComplexMapPairKeyType_thenGetAMapBetweenPairAndList() {
Map<Pair<BlogPostType, String>, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
.collect(groupingBy(post -> new ImmutablePair<>(post.getType(), post.getAuthor())));
List<BlogPost> result = postsPerTypeAndAuthor.get(new ImmutablePair<>(BlogPostType.GUIDE, "Author 1"));
assertThat(result.size()).isEqualTo(1);
BlogPost blogPost = result.get(0);
assertThat(blogPost.getTitle()).isEqualTo("Programming guide");
assertThat(blogPost.getType()).isEqualTo(BlogPostType.GUIDE);
assertThat(blogPost.getAuthor()).isEqualTo("Author 1");
}
@Test
public void givenAListOfPosts_whenGroupedByComplexMapKeyType_thenGetAMapBetweenTupleAndList() {
Map<Tuple, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
.collect(groupingBy(post -> new Tuple(post.getType(), post.getAuthor())));
List<BlogPost> result = postsPerTypeAndAuthor.get(new Tuple(BlogPostType.GUIDE, "Author 1"));
assertThat(result.size()).isEqualTo(1);
BlogPost blogPost = result.get(0);
assertThat(blogPost.getTitle()).isEqualTo("Programming guide");
assertThat(blogPost.getType()).isEqualTo(BlogPostType.GUIDE);
assertThat(blogPost.getAuthor()).isEqualTo("Author 1");
}
@Test
public void givenAListOfPosts_whenGroupedByRecord_thenGetAMapBetweenRecordAndList() {
Map<BlogPost.AuthPostTypesLikes, List<BlogPost>> postsPerTypeAndAuthor = posts.stream()
.collect(groupingBy(post -> new BlogPost.AuthPostTypesLikes(post.getAuthor(), post.getType(), post.getLikes())));
List<BlogPost> result = postsPerTypeAndAuthor.get(new BlogPost.AuthPostTypesLikes("Author 1", BlogPostType.GUIDE, 20));
assertThat(result.size()).isEqualTo(1);
BlogPost blogPost = result.get(0);
assertThat(blogPost.getTitle()).isEqualTo("Programming guide");
assertThat(blogPost.getType()).isEqualTo(BlogPostType.GUIDE);
assertThat(blogPost.getAuthor()).isEqualTo("Author 1");
assertThat(blogPost.getLikes()).isEqualTo(20);
}
}