Here you can find the source of findFreePort()
public static int findFreePort() throws Exception
//package com.java2s; /*/*from w w w . j a v a 2 s. co m*/ * ProActive Parallel Suite(TM): * The Open Source library for parallel and distributed * Workflows & Scheduling, Orchestration, Cloud Automation * and Big Data Analysis on Enterprise Grids & Clouds. * * Copyright (c) 2007 - 2017 ActiveEon * Contact: contact@activeeon.com * * This library is free software: you can redistribute it and/or * modify it under the terms of the GNU Affero General Public License * as published by the Free Software Foundation: version 3 of * the License. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Affero General Public License for more details. * * You should have received a copy of the GNU Affero General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. * * If needed, contact us to obtain a release under GPL Version 2 or 3 * or a different license than the AGPL. */ import java.io.Closeable; import java.io.IOException; import java.net.ServerSocket; public class Main { public static int findFreePort() throws Exception { ServerSocket s = new ServerSocket(0); s.close(); return s.getLocalPort(); } private static void close(Closeable stream) { try { stream.close(); } catch (IOException ioe) { System.err.println("An error occurred while closing the stream."); ioe.printStackTrace(); } } }