BAEL-5557 Split a stream into parts (#12238)

* BAEL-5557 Split a stream into parts

* BAEL-5557 fix main pom.xml

* BAEL-5557 fix mvn profiles

* BAEL-5557 articles with equals and hashcode

* BAEL-5557 migrate assertions to assertj

* BAEL-5557 better assertions

core-java-modules/core-java-streams-4/src/test/java/splitting/Article.java

@@ -0,0 +1,37 @@
+package splitting;
+
+class Article {
+    private final String target;
+    private final boolean featured;
+
+    public Article(String target, boolean featured) {
+        this.target = target;
+        this.featured = featured;
+    }
+
+    public String getTarget() {
+        return target;
+    }
+
+    public boolean isFeatured() {
+        return featured;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+
+        Article article = (Article) o;
+
+        if (featured != article.featured) return false;
+        return target.equals(article.target);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = target.hashCode();
+        result = 31 * result + (featured ? 1 : 0);
+        return result;
+    }
+}

core-java-modules/core-java-streams-4/src/test/java/splitting/StreamSplittingUnitTest.java

@@ -0,0 +1,95 @@
+package splitting;
+
+import com.google.common.collect.Lists;
+import org.junit.Test;
+import rx.Observable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class StreamSplittingUnitTest {
+    private final static List<Article> articles = Lists.newArrayList(
+            new Article("Baeldung", true),
+            new Article("Baeldung", false),
+            new Article("Programming Daily", false),
+            new Article("The Code", false)
+    );
+
+    @Test
+    public void givenListOfArticles_shouldSplitListInTwoCategories_usingPartitioningBy() {
+        Map<Boolean, List<Article>> groupedArticles = articles.stream().collect(Collectors.partitioningBy(a -> a.getTarget().equals("Baeldung")));
+
+        assertThat(groupedArticles.get(true)).containsExactly(
+                new Article("Baeldung", true),
+                new Article("Baeldung", false));
+        assertThat(groupedArticles.get(false)).containsExactly(
+                new Article("Programming Daily", false),
+                new Article("The Code", false));
+    }
+
+    @Test
+    public void givenListOfArticles_shouldSplitListInMultipleCategories_usingGroupingBy() {
+        Map<String, List<Article>> groupedArticles = articles.stream().collect(Collectors.groupingBy(Article::getTarget));
+
+        assertThat(groupedArticles.get("Baeldung")).hasSize(2);
+        assertThat(groupedArticles.get("Programming Daily")).hasSize(1);
+        assertThat(groupedArticles.get("The Code")).hasSize(1);
+
+        assertThat(groupedArticles.get("Baeldung")).containsExactly(
+                new Article("Baeldung", true),
+                new Article("Baeldung", false));
+        assertThat(groupedArticles.get("Programming Daily")).containsExactly(new Article("Programming Daily", false));
+        assertThat(groupedArticles.get("The Code")).containsExactly(new Article("The Code", false));
+    }
+
+    @Test
+    public void givenListOfArticles_shouldSplitListInTwoCategories_usingTeeing() {
+        List<Long> countedArticles = articles.stream().collect(Collectors.teeing(
+                Collectors.filtering(article -> article.getTarget().equals("Baeldung"), Collectors.counting()),
+                Collectors.filtering(article -> !article.getTarget().equals("Baeldung"), Collectors.counting()),
+                List::of));
+
+        assertThat(countedArticles.get(0)).isEqualTo(2);
+        assertThat(countedArticles.get(1)).isEqualTo(2);
+    }
+
+    @Test
+    public void givenListOfArticles_shouldSplitListInTwoOVerlappingCategories_usingTeeing() {
+        List<List<Article>> groupedArticles = articles.stream().collect(Collectors.teeing(
+                Collectors.filtering(article -> article.getTarget().equals("Baeldung"), Collectors.toList()),
+                Collectors.filtering(Article::isFeatured, Collectors.toList()),
+                List::of));
+
+        assertThat(groupedArticles.get(0)).hasSize(2);
+        assertThat(groupedArticles.get(1)).hasSize(1);
+
+        assertThat(groupedArticles.get(0)).containsExactly(
+                new Article("Baeldung", true),
+                new Article("Baeldung", false));
+        assertThat(groupedArticles.get(1)).containsExactly(new Article("Baeldung", true));
+    }
+
+    @Test
+    public void givenListOfArticles_shouldSplitStreamInMultipleCategories_usingRxJava() {
+        Observable<Article> observableArticles = Observable.from(articles);
+
+        Observable<Article> baeldungObservable = observableArticles.filter(article -> article.getTarget().equals("Baeldung"));
+        Observable<Article> featuredObservable = observableArticles.filter(Article::isFeatured);
+        List<Article> baeldungArticles = new ArrayList<>();
+        List<Article> featuredArticles = new ArrayList<>();
+        baeldungObservable.subscribe(baeldungArticles::add);
+        featuredObservable.subscribe(featuredArticles::add);
+
+        assertThat(baeldungArticles).hasSize(2);
+        assertThat(featuredArticles).hasSize(1);
+
+        assertThat(baeldungArticles).containsExactly(
+                        new Article("Baeldung", true),
+                        new Article("Baeldung", false));
+        assertThat(featuredArticles).containsExactly(new Article("Baeldung", true));
+    }
+}