Java HTTP Port Find getUnusedPort(int startPort)

Description

Returns an unused port number on the local host.

License

LGPL

Parameter

Parameter	Description
startPort	suggested port number; ports nearby will be chosen if this is in use

Declaration

static int getUnusedPort(int startPort) throws IOException 

Method Source Code

//package com.java2s;
//License from project: LGPL 

import java.io.IOException;

import java.net.ConnectException;

import java.net.Socket;

public class Main {
    /**/*from   w w w .j  ava 2s.  c o m*/
     * True if spurious java.util.NoSuchElementExceptions should be flagged.
     * If future JVMs fix this bug, this should be set false or the code
     * removed.
     */
    public static boolean WARN_ABOUT_NOSUCHELEMENTEXCEPTIONS = true;

    /**
     * Returns an unused port number on the local host.
     *
     * @param   startPort  suggested port number; ports nearby will be
     *          chosen if this is in use
     */
    static int getUnusedPort(int startPort) throws IOException {
        final int nTry = 20;
        for (int iPort = startPort; iPort < startPort + nTry; iPort++) {
            try {
                Socket trySocket = new Socket("localhost", iPort);
                if (!trySocket.isClosed()) {

                    /* This line causes "java.util.NoSuchElementException" to
                     * be written to System.err, at least at J2SE1.4.
                     * Not my fault! */
                    if (WARN_ABOUT_NOSUCHELEMENTEXCEPTIONS) {
                        WARN_ABOUT_NOSUCHELEMENTEXCEPTIONS = false;
                        System.err.println(
                                "Please ignore spurious \"" + "java.util.NoSuchElementException\" messages.");
                    }
                    trySocket.close();
                }
            } catch (ConnectException e) {

                /* Can't connect - this hopefully means that the socket is
                 * unused. */
                return iPort;
            }
        }
        throw new IOException("Can't locate an unused port in range " + startPort + " ... " + (startPort + nTry));
    }
}

Related

1. getServerPort()
2. getSupportedConnectionTypes(Map map)
3. getSupportedEntityTypes()
4. getUnusedPort()
5. getUnusedPort(final int start)
6. getUnusedPorts(final int count, final int start)
7. getValidZooKeeperPort()
8. getWsdlLocation(String portPrefix)
9. getXmlReport(String fileName)