Java HTTP Port Find getFreePort()

Description

Get an arbitrary free port on the localhost

License

Open Source License

Exception

Parameter	Description
IllegalArgumentException	if no free port could be found

Return

free port

Declaration

public static int getFreePort() throws IOException 

Method Source Code

//package com.java2s;
/*/*from   w w  w .j a  v  a 2  s.co m*/
 * Copyright 2009-2011 Roland Huss
 *
 *  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.
 */

import java.io.*;
import java.net.*;

public class Main {
    /**
     * Get an arbitrary free port on the localhost
     *
     * @return free port
     * @throws IllegalArgumentException if no free port could be found
     */
    public static int getFreePort() throws IOException {
        for (int port = 22332; port < 22500; port++) {
            if (trySocket(port)) {
                return port;
            }
        }
        throw new IllegalStateException("Cannot find a single free port");
    }

    /**
     * Try a given port on the localhost and check whether it is free
     *
     * @param port port to check
     * @return true if the port is still free
     */
    @SuppressWarnings({ "PMD.SystemPrintln" })
    public static boolean trySocket(int port) throws IOException {
        InetAddress address = Inet4Address.getByName("localhost");
        try (ServerSocket s = new ServerSocket()) {
            s.bind(new InetSocketAddress(address, port));
            return true;
        } catch (IOException exp) {
            System.err.println("Port " + port + " already in use, trying next ...");
        }
        return false;
    }
}

Related

1. getFreePort()
2. getFreePort()
3. getFreePort()
4. getFreePort()
5. getFreePort()
6. getFreePort()
7. getFreePort()
8. getFreePort()
9. getFreePort()