BAEL-4504: Move find free port to networking-3

core-java-modules/core-java-networking-3/README.md

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+## Core Java Networking (Part 3)
+
+This module contains articles about networking in Java
+
+### Relevant Articles
+
+- TODO: add link once live
+- [[<-- Prev]](/core-java-modules/core-java-networking-2)

core-java-modules/core-java-networking-3/pom.xml

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+<?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-networking-4</artifactId>
+    <name>core-java-networking-3</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../pom.xml</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-core</artifactId>
+            <version>${spring.core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.jetty</groupId>
+            <artifactId>jetty-server</artifactId>
+            <version>${jetty.embeded.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.tomcat.embed</groupId>
+            <artifactId>tomcat-embed-core</artifactId>
+            <version>${tomcat.embeded.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-networking-3</finalName>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <spring.core.version>5.2.8.RELEASE</spring.core.version>
+        <jetty.embeded.version>9.4.31.v20200723</jetty.embeded.version>
+        <tomcat.embeded.version>10.0.0-M7</tomcat.embeded.version>
+        <assertj.version>3.11.1</assertj.version>
+    </properties>
+
+</project>

core-java-modules/core-java-networking-3/src/test/java/com/baeldung/socket/FindFreePortUnitTest.java

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+package com.baeldung.socket;
+
+import org.apache.catalina.LifecycleException;
+import org.apache.catalina.startup.Tomcat;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.ServerConnector;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.springframework.util.SocketUtils;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+
+import static org.assertj.core.api.Assertions.*;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class FindFreePortUnitTest {
+
+    private static int FREE_PORT_NUMBER;
+    private static int[] FREE_PORT_RANGE;
+
+    @BeforeAll
+    public static void getExplicitFreePortNumberAndRange() {
+        try (ServerSocket serverSocket = new ServerSocket(0);) {
+            FREE_PORT_NUMBER = serverSocket.getLocalPort();
+            FREE_PORT_RANGE = new int[] {FREE_PORT_NUMBER, FREE_PORT_NUMBER + 1, FREE_PORT_NUMBER + 2};
+        } catch (IOException e) {
+            fail("No free port is available");
+        }
+    }
+
+    @Test
+    public void givenExplicitFreePort_whenCreatingServerSocket_thenThatPortIsAssigned() {
+        try (ServerSocket serverSocket = new ServerSocket(FREE_PORT_NUMBER);) {
+            assertThat(serverSocket).isNotNull();
+            assertThat(serverSocket.getLocalPort()).isEqualTo(FREE_PORT_NUMBER);
+        } catch (IOException e) {
+            fail("Port is not available");
+        }
+    }
+
+    @Test
+    public void givenExplicitOccupiedPort_whenCreatingServerSocket_thenExceptionIsThrown() {
+        try (ServerSocket serverSocket = new ServerSocket(FREE_PORT_NUMBER)) {
+            new ServerSocket(FREE_PORT_NUMBER);
+            fail("Same port cannot be used twice");
+        } catch (IOException e) {
+            assertThat(e).hasMessageContaining("Address already in use");
+        }
+    }
+
+    @Test
+    public void givenExplicitPortRange_whenCreatingServerSocket_thenOnePortIsAssigned() {
+        for (int port : FREE_PORT_RANGE) {
+            try (ServerSocket serverSocket = new ServerSocket(port)) {
+                assertThat(serverSocket).isNotNull();
+                assertThat(serverSocket.getLocalPort()).isGreaterThan(0);
+                return;
+            } catch (IOException e) {
+                assertThat(e).hasMessageContaining("Address already in use");
+            }
+        }
+        fail("No free port in the range found");
+    }
+
+    @Test
+    public void givenPortZero_whenCreatingServerSocket_thenFreePortIsAssigned() {
+        try (ServerSocket serverSocket = new ServerSocket(0)) {
+            assertThat(serverSocket).isNotNull();
+            assertThat(serverSocket.getLocalPort()).isGreaterThan(0);
+        } catch (IOException e) {
+            fail("Port is not available");
+        }
+    }
+
+    @Test
+    public void givenAvailableTcpPort_whenCreatingServerSocket_thenThatPortIsAssigned() {
+        int port = SocketUtils.findAvailableTcpPort();
+        try (ServerSocket serverSocket = new ServerSocket(port)) {
+            assertThat(serverSocket).isNotNull();
+            assertThat(serverSocket.getLocalPort()).isGreaterThan(0);
+        } catch (IOException e) {
+            fail("Port is not available");
+        }
+    }
+
+    @Test
+    public void givenNoPortDefined_whenCreatingJettyServer_thenFreePortIsAssigned() {
+        Server jettyServer = new Server();
+        ServerConnector serverConnector = new ServerConnector(jettyServer);
+        jettyServer.addConnector(serverConnector);
+        try {
+            jettyServer.start();
+            assertThat(serverConnector.getLocalPort()).isGreaterThan(0);
+            jettyServer.stop();
+            jettyServer.destroy();
+        } catch (Exception e) {
+            fail("Failed to start Jetty server");
+        }
+    }
+
+    @Test
+    public void givenExplicitFreePort_whenCreatingJettyServer_thenThatPortIsAssigned() {
+        Server jettyServer = new Server();
+        ServerConnector serverConnector = new ServerConnector(jettyServer);
+        serverConnector.setPort(FREE_PORT_NUMBER);
+        jettyServer.addConnector(serverConnector);
+        try {
+            jettyServer.start();
+            assertThat(serverConnector.getLocalPort()).isEqualTo(FREE_PORT_NUMBER);
+            jettyServer.stop();
+            jettyServer.destroy();
+        } catch (Exception e) {
+            fail("Failed to start Jetty server");
+        }
+    }
+
+    @Test
+    public void givenPortZero_whenCreatingTomcatServer_thenFreePortIsAssigned() {
+        Tomcat tomcatServer = new Tomcat();
+        tomcatServer.setPort(0);
+        try {
+            tomcatServer.start();
+            assertThat(tomcatServer.getConnector().getLocalPort()).isGreaterThan(0);
+            tomcatServer.stop();
+            tomcatServer.destroy();
+        } catch (LifecycleException e) {
+            fail("Failed to start Tomcat server");
+        }
+    }
+
+    @Test
+    public void givenExplicitFreePort_whenCreatingTomcatServer_thenThatPortIsAssigned() {
+        Tomcat tomcatServer = new Tomcat();
+        tomcatServer.setPort(FREE_PORT_NUMBER);
+        try {
+            tomcatServer.start();
+            assertThat(tomcatServer.getConnector().getLocalPort()).isEqualTo(FREE_PORT_NUMBER);
+            tomcatServer.stop();
+            tomcatServer.destroy();
+        } catch (LifecycleException e) {
+            fail("Failed to start Tomcat server");
+        }
+    }
+
+}