PortFinder.java

/*
 * Copyright (C) 2012-2016 DuyHai DOAN
 *
 * 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 info.archinnov.achilles.embedded;

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

public class PortFinder {

    private static int MAX_TRIES = 100;

    public static int randomAvailable() {
        return findAvailableBetween(1025, 65534);
    }

    public static Integer findAvailableBetween(int start, int end) {
        int tested = randomBetween(start, end);

        for (int i = 0; i < MAX_TRIES; i++) {
            if (isAvailable(tested)) {
                return tested;
            }
            tested = randomBetween(start, end);
        }
        throw new IllegalStateException("no available port found between " + start + " and " + end + " after "
                + MAX_TRIES + "tries");
    }

    /**
     * http://stackoverflow.com/questions/434718/sockets-discover-port-
     * availability-using-java
     */
    public static boolean isAvailable(int port) {
        ServerSocket ss = null;
        DatagramSocket ds = null;
        try {
            ss = new ServerSocket(port);
            ss.setReuseAddress(true);
            ds = new DatagramSocket(port);
            ds.setReuseAddress(true);
            return true;
        } catch (IOException e) {
        } finally {
            if (ds != null) {
                ds.close();
            }

            if (ss != null) {
                try {
                    ss.close();
                } catch (IOException e) {
                    /* should not be thrown */
                }
            }
        }

        return false;
    }

    private static int randomBetween(int start, int end) {
        return start + (int) (Math.random() * ((end - start) + 1));
    }

}