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Bael 5066 aggregate over multiple fields (#11156) 

* Commit source code to branch

* BAEL-5065 improvement of groupBy with complex key

* Aggregation of multiple attributes of a grouped result
This commit is contained in:
mbarriola 2021-08-22 16:57:09 -04:00 committed by GitHub
parent b180037cdc
commit 70283b1191
2 changed files with 61 additions and 8 deletions
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5
core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/groupingby/BlogPost.java
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@ -1,5 +1,8 @@
package com.baeldung.java_16_features.groupingby; package com.baeldung.java_16_features.groupingby;
import java.util.IntSummaryStatistics;
public class BlogPost { public class BlogPost {
private String title; private String title;
@ -7,6 +10,8 @@ public class BlogPost {
private BlogPostType type; private BlogPostType type;
private int likes; private int likes;
record AuthPostTypesLikes(String author, BlogPostType type, int likes) {}; record AuthPostTypesLikes(String author, BlogPostType type, int likes) {};
record PostcountTitlesLikesStats(long postCount, String titles, IntSummaryStatistics likesStats){};
record TitlesBoundedSumOfLikes(String titles, int boundedSumOfLikes) {};
public BlogPost(String title, String author, BlogPostType type, int likes) { public BlogPost(String title, String author, BlogPostType type, int likes) {
this.title = title; this.title = title;

48
core-java-modules/core-java-16/src/test/java/com/baeldung/java_16_features/groupingby/JavaGroupingByCollectorUnitTest.java
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@ -5,6 +5,8 @@ import static java.util.stream.Collectors.averagingInt;
import static java.util.stream.Collectors.counting; import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy; import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.groupingByConcurrent; import static java.util.stream.Collectors.groupingByConcurrent;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.toMap;
import static java.util.stream.Collectors.joining; import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.mapping; import static java.util.stream.Collectors.mapping;
import static java.util.stream.Collectors.maxBy; import static java.util.stream.Collectors.maxBy;
@ -13,6 +15,7 @@ import static java.util.stream.Collectors.summingInt;
import static java.util.stream.Collectors.toList; import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toSet; import static java.util.stream.Collectors.toSet;
import static org.assertj.core.api.Assertions.assertThat; import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.offset;
import static org.junit.jupiter.api.Assertions.assertEquals; import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNull; import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertTrue; import static org.junit.jupiter.api.Assertions.assertTrue;
@ -251,4 +254,49 @@ public class JavaGroupingByCollectorUnitTest {
assertThat(blogPost.getLikes()).isEqualTo(20); assertThat(blogPost.getLikes()).isEqualTo(20);
} }
@Test
public void givenListOfPosts_whenGroupedByAuthor_thenGetAMapUsingCollectingAndThen() {
Map<String, BlogPost.PostcountTitlesLikesStats> postsPerAuthor = posts.stream()
.collect(groupingBy(BlogPost::getAuthor, collectingAndThen(toList(), list -> {
long count = list.stream()
.map(BlogPost::getTitle)
.collect(counting());
String titles = list.stream()
.map(BlogPost::getTitle)
.collect(joining(" : "));
IntSummaryStatistics summary = list.stream()
.collect(summarizingInt(BlogPost::getLikes));
return new BlogPost.PostcountTitlesLikesStats(count, titles, summary);
})));
BlogPost.PostcountTitlesLikesStats result = postsPerAuthor.get("Author 1");
assertThat(result.postCount()).isEqualTo(3L);
assertThat(result.titles()).isEqualTo("News item 1 : Programming guide : Tech review 2");
assertThat(result.likesStats().getMax()).isEqualTo(20);
assertThat(result.likesStats().getMin()).isEqualTo(15);
assertThat(result.likesStats().getAverage()).isEqualTo(16.666d, offset(0.001d));
}
@Test
public void givenListOfPosts_whenGroupedByAuthor_thenGetAMapUsingToMap() {
int maxValLikes = 17;
Map<String, BlogPost.TitlesBoundedSumOfLikes> postsPerAuthor = posts.stream()
.collect(toMap(BlogPost::getAuthor, post -> {
int likes = (post.getLikes() > maxValLikes) ? maxValLikes : post.getLikes();
return new BlogPost.TitlesBoundedSumOfLikes(post.getTitle(), likes);
}, (u1, u2) -> {
int likes = (u2.boundedSumOfLikes() > maxValLikes) ? maxValLikes : u2.boundedSumOfLikes();
return new BlogPost.TitlesBoundedSumOfLikes(u1.titles()
.toUpperCase() + " : "
+ u2.titles()
.toUpperCase(),
u1.boundedSumOfLikes() + likes);
}));
BlogPost.TitlesBoundedSumOfLikes result = postsPerAuthor.get("Author 1");
assertThat(result.titles()).isEqualTo("NEWS ITEM 1 : PROGRAMMING GUIDE : TECH REVIEW 2");
assertThat(result.boundedSumOfLikes()).isEqualTo(47);
}
} }