ServerSocketUtil.java

/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2013, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.net.server;

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

import javax.net.ServerSocketFactory;

/**
 * Static utility methods for obtaining a {@link ServerSocket} bound to
 * a random unused port.
 *
 * @author Carl Harris
 */
public class ServerSocketUtil {

  /**
   * Creates a new {@link ServerSocket} bound to a random unused port.
   * <p>
   * This method is a convenience overload for
   * {@link #createServerSocket(ServerSocketFactory)} using the platform's
   * default {@link ServerSocketFactory}.
   * @return socket
   * @throws IOException
   */
  public static ServerSocket createServerSocket() throws IOException {
    return createServerSocket(ServerSocketFactory.getDefault());
  }

  /**
   * Creates a new {@link ServerSocket} bound to a random unused port.
   * @param socketFactory socket factory that will be used to create the
   *    socket
   * @return socket
   * @throws IOException
   */
  public static ServerSocket createServerSocket(
      ServerSocketFactory socketFactory) throws IOException {
    ServerSocket socket = null;
    int retries = 10;
    while (retries-- > 0 && socket == null) {
      int port = (int)((65536 - 1024) * Math.random()) + 1024;
      try {
        socket = socketFactory.createServerSocket(port);
      }
      catch (BindException ex) {
        // try again with different port
      }
    }
    if (socket == null) {
      throw new BindException("cannot find an unused port to bind");
    }
    return socket;
  }

}