Here you can find the source of getAnonymousPort()
java.net.ServerSocket
with a port of 0
public static int getAnonymousPort() throws java.io.IOException
//package com.java2s; /*//from w ww.j a v a 2s. c o m * Copyright (c) 2008-2016, GigaSpaces Technologies, Inc. All Rights Reserved. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ public class Main { /** * Get an anonymous socket port. * * @return An anonymous port created by instantiating a <code>java.net.ServerSocket</code> with * a port of 0 */ public static int getAnonymousPort() throws java.io.IOException { java.net.ServerSocket socket = new java.net.ServerSocket(0); int port = socket.getLocalPort(); socket.close(); return port; } }