Grouping by collector java (#10986)

* Initial Commit - Ports and Adapters

* Restructured code to implement input and outbou ports and adapters

* Added tests for groupingBy Collector

* Revert "Initial Commit - Ports and Adapters"

This reverts commit 55152dea

* Added tests for groupingBy Collector

* reverting

* corrected typo

* used BDD naming strategy for tests

* Added a test for groupingByConcurrent

* added new module and package

* added core-java-streams-4 module in main pom.xml

* updated pom.xml and changed artifactId

core-java-modules/core-java-streams-4/pom.xml

@@ -0,0 +1,63 @@
+<?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-streams-4</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-streams</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit</groupId>
+            <artifactId>junit-bom</artifactId>
+            <version>${junit-jupiter.version}</version>
+            <type>pom</type>
+            <scope>import</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-streams-4</finalName>
+        <resources>
+            <resource>
+                <directory>src/main</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                    <compilerArgument>-parameters</compilerArgument>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <!-- testing -->
+        <maven-compiler-plugin.version>3.1</maven-compiler-plugin.version>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+    </properties>
+
+</project>