Merge pull request #6569 from alimate/BAEL-2786

Teeing Collector

core-java-12/pom.xml

@@ -0,0 +1,48 @@
+<?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>
+	<groupId>com.baeldung</groupId>
+	<artifactId>core-java-12</artifactId>
+	<version>0.1.0-SNAPSHOT</version>
+	<name>core-java-12</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>
+	</parent>
+
+	<dependencies>
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<version>${assertj.version}</version>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-compiler-plugin</artifactId>
+				<version>${maven-compiler-plugin.version}</version>
+				<configuration>
+					<source>${maven.compiler.source.version}</source>
+					<target>${maven.compiler.target.version}</target>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+
+	<properties>
+		<maven.compiler.source.version>12</maven.compiler.source.version>
+		<maven.compiler.target.version>12</maven.compiler.target.version>
+		<assertj.version>3.6.1</assertj.version>
+	</properties>
+
+</project>

core-java-12/src/test/java/com/baeldung/collectors/CollectorsUnitTest.java

@@ -0,0 +1,77 @@
+package com.baeldung.collectors;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+
+import org.junit.Test;
+
+import static java.util.stream.Collectors.maxBy;
+import static java.util.stream.Collectors.minBy;
+import static java.util.stream.Collectors.teeing;
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for collectors additions in Java 12.
+ */
+public class CollectorsUnitTest {
+
+	@Test
+	public void whenTeeing_ItShouldCombineTheResultsAsExpected() {
+		List<Integer> numbers = Arrays.asList(42, 4, 2, 24);
+		Range range = numbers.stream()
+				.collect(teeing(
+						minBy(Integer::compareTo),
+						maxBy(Integer::compareTo),
+						(min, max) -> new Range(min.orElse(null), max.orElse(null))
+				));
+
+		assertThat(range).isEqualTo(new Range(2, 42));
+	}
+
+	/**
+	 * Represents a closed range of numbers between {@link #min} and
+	 * {@link #max}, both inclusive.
+	 */
+	private static class Range {
+
+		private final Integer min;
+
+		private final Integer max;
+
+		Range(Integer min, Integer max) {
+			this.min = min;
+			this.max = max;
+		}
+
+		Integer getMin() {
+			return min;
+		}
+
+		Integer getMax() {
+			return max;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (this == o) return true;
+			if (o == null || getClass() != o.getClass()) return false;
+			Range range = (Range) o;
+			return Objects.equals(getMin(), range.getMin()) &&
+					Objects.equals(getMax(), range.getMax());
+		}
+
+		@Override
+		public int hashCode() {
+			return Objects.hash(getMin(), getMax());
+		}
+
+		@Override
+		public String toString() {
+			return "Range{" +
+					"min=" + min +
+					", max=" + max +
+					'}';
+		}
+	}
+}

pom.xml

@@ -377,6 +377,7 @@
                 <module>core-groovy</module>
                 <!-- <module>core-java-10</module> --> <!-- We haven't upgraded to java 10. Fixing in BAEL-10841 -->
                 <!-- <module>core-java-11</module> --> <!-- We haven't upgraded to java 11. Fixing in BAEL-10841 --> 
+                <!-- <module>core-java-12</module> --> <!-- We haven't upgraded to java 12. Fixing in BAEL-10841 -->
                 <module>core-java-8</module>
                 <!--<module>core-java-9</module> --> <!-- We haven't upgraded to java 9. Fixing in BAEL-10841 -->
                 <!--<module>core-java-os</module> --> <!-- We haven't upgraded to java 9.-->