Here you can find the source of getNextAvailablePort(InetAddress address, int port)
| Parameter | Description |
|---|---|
| address | The address on which to find the next available port |
| port | The number of the port on which to start looking |
public static int getNextAvailablePort(InetAddress address, int port)
//package com.java2s; /*//from www . ja va 2s . co m * Copyright (c) 2006 Stephan D. Cote' - All rights reserved. * * This program and the accompanying materials are made available under the * terms of the MIT License which accompanies this distribution, and is * available at http://creativecommons.org/licenses/MIT/ * * Contributors: * Stephan D. Cote * - Initial API and implementation */ import java.io.IOException; import java.net.InetAddress; import java.net.ServerSocket; import java.net.UnknownHostException; public class Main { private static InetAddress localAddress = null; /** * Return a port number that can be used to create a socket on the given * address starting with port 1. * * @param address The address on which to find the next available port * * @return the next available port on the given address */ public static int getNextAvailablePort(InetAddress address) { return getNextAvailablePort(address, 1); } /** * Return a port number that can be used to create a socket with the given * port on the local address. * * <p>If you are looking for port 80, but it is taken, this method will * return the next higher port starting with that port. This will keep your * ports grouped together. * * @param port The number of the port on which to start looking * * @return the next available port on the local address. */ public static int getNextAvailablePort(int port) { return getNextAvailablePort(null, port); } /** * Return a port number that can be used to create a socket on the given * address starting with the given port. * * <p>If the given port can be used to create a server socket (TCP) then that * port number will be used, otherwise, the port number will be incremented * and tested until a free port is found. * * <p>This is not thread-safe nor fool-proof. A valid value can be returned, * yet when a call is made to open a socket at that port, another thread may * have already opened a socket on that port. A better way would be to use * the <code>getNextServerSocket(address,port)</code> method if it desired to * obtain the next available server. * * @param address The address on which to find the next available port * @param port The number of the port on which to start looking * * @return the next available port on the given address. */ public static int getNextAvailablePort(InetAddress address, int port) { ServerSocket socket = getNextServerSocket(address, port, 0); int retval = -1; if (socket != null) { // Get the port as a return value retval = socket.getLocalPort(); // Close the un-needed socket try { socket.close(); } catch (IOException e) { // Ignore it } } return retval; } /** * Return a TCP server socket on the given address and port, incrementing the * port until a server socket can be opened. * * @param address The address on which to find the next available port * @param port The number of the port on which to start looking * @param backlog requested maximum length of the queue of incoming connections. * * @return the next available port on the local address. */ public static ServerSocket getNextServerSocket(InetAddress address, int port, int backlog) { int i = port; ServerSocket socket = null; // If no address was given, then try to determine our local address so we // can use our main address instead of 127.0.0.1 which may be chosen by the // VM if it is not specified in the ServerSocket constructor if (address == null) { address = getLocalAddress(); } while (validatePort(i) != 0) { try { if (address == null) { socket = new ServerSocket(i, backlog); } else { socket = new ServerSocket(i, backlog, address); } if (socket != null) { return socket; } } catch (IOException e) { i++; } } return null; } /** * Get the IP Address by which the rest of the world knows us. * * <p>This is useful in helping insure that we don't accidently start binding * to or otherwise using the local loopback address. * * <p>This requires some type of IP address resolver to be installed, like * DNS, NIS or at least hostname lookup. * * @return The InetAddress representing the host on the network and NOT the * loopback address. */ public static InetAddress getLocalAddress() { // If we already looked this up, use the cached result to save time if (localAddress != null) { return localAddress; } // No cached result, figure it out and cache it for later InetAddress addr = null; // Make sure we get the IP Address by which the rest of the world knows us // or at least, our host's default network interface try { // This helps insure that we do not get localhost (127.0.0.1) addr = InetAddress.getByName(InetAddress.getLocalHost().getHostName()); } catch (UnknownHostException e) { // Aaaaww Phooey! DNS is not working or we are not in it. addr = null; } // If it looks like a unique address, return it, otherwise try again if ((addr != null) && !addr.getHostAddress().equals("127.0.0.1") && !addr.getHostAddress().equals("0.0.0.0")) { localAddress = addr; return addr; } // Try it the way it's supposed to work try { addr = InetAddress.getLocalHost(); } catch (Exception ex) { addr = null; } localAddress = addr; return addr; } /** * Validate if the port is within the valid range for an IP port. * * @param port the port to check * * @return the value of the port if it is within range, 0 otherwise. */ public static int validatePort(int port) { if ((port < 0) || (port > 0xFFFF)) { return 0; } else { return port; } } }