RandomPortNumberGenerator.java

/*
 * Copyright (C) 2011 Benoit GUEROUT <bguerout at gmail dot com> and Yves AMSELLEM <amsellem dot yves at gmail dot com>
 *
 * 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.
 */

package org.jongo.util;


import java.io.IOException;
import java.net.DatagramSocket;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;

/**
 * Picks up a port number from the ephemeral port range.
 * http://en.wikipedia.org/wiki/Ephemeral_port
 *
 * @author Alexandre Dutra
 */
public class RandomPortNumberGenerator {

    private static final int MAX_PORT_NUMBER = 61000;
    private static final int MIN_PORT_NUMBER = 49152;

    /**
     * Pick a random available port number in the ephemeral port range,
     * i.e. between {@value #MIN_PORT_NUMBER} inclusively and
     * {@value #MAX_PORT_NUMBER} exclusively.
     *
     * @return a random available port number in the ephemeral port range
     */
    public static int pickAvailableRandomEphemeralPortNumber() {
        return pickAvailableRandomPortNumber(MIN_PORT_NUMBER, MAX_PORT_NUMBER);
    }


    /**
     * Pick a random available port number between
     * {@code min} inclusively and {@code max} exclusively.
     *
     * @return a random available port number between {@code min} inclusively and
     * {@code max} exclusively
     */
    public static int pickAvailableRandomPortNumber(int min, int max) {
        while (true) {
            int port = pickRandomPortNumber(min, max);
            if (isPortAvailable(port)) {
                return port;
            }
        }
    }

    /**
     * Pick a random port number between {@code min} inclusively and
     * {@code max} exclusively.
     *
     * @return a random port number between {@code min} inclusively and
     * {@code max} exclusively
     */
    public static int pickRandomPortNumber(int min, int max) {
        return ((int) (Math.random() * (max - min))) + min;
    }

    /**
     * Test whether a port number is available (i.e. not bound).
     *
     * @return a random port number between {@code min} inclusively and
     * {@code max} exclusively
     */
    public static boolean isPortAvailable(int port) {
        ServerSocket ss = null;
        DatagramSocket ds = null;
        try {
            ss = new ServerSocket(port);
            ss.setReuseAddress(true);
            ds = new DatagramSocket(port);
            ds.setReuseAddress(true);
        } catch (IOException e) {
            return false;
        } finally {
            if (ds != null) {
                ds.close();
            }
            if (ss != null) {
                try {
                    ss.close();
                } catch (IOException e) {
                }
            }
        }
        try {
            new Socket("localhost", port);
        } catch (UnknownHostException e) {
            return false;
        } catch (IOException e) {
            return true;
        }

        return false;
    }

}