Find next available TCP port.

PortUtil.java

import java.net.ServerSocket;

class PortUtil {

  private PortUtil() {}

  /**
   * Recursively loops until finding a available TCP port, locks it, get 
   * its value and then releases it.
   * 
   * @return next available port.
   */
  static int nextAvailablePort() {
    try (var s = new ServerSocket(0)) {
      return s.getLocalPort();
    } catch (final IOException e) {
      return nextAvailablePort();
    }
  }
}