Here you can find the source of getAvailablePort()
public static int getAvailablePort() throws IOException
//package com.java2s; /*/*from www. j av a2 s .c o m*/ * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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. */ import java.io.IOException; import java.net.ServerSocket; public class Main { public static int getAvailablePort() throws IOException { for (int i = 0; i < 50; i++) { ServerSocket serverSocket = null; try { serverSocket = new ServerSocket(0); int port = serverSocket.getLocalPort(); if (port != 0) { return port; } } finally { serverSocket.close(); } } throw new IOException("could not find free port"); } }