方法一：如果你不介意获取的端口号范围，可以使用 DatagramSocket 的构造方法定义 0 为其端口号，系统将为其分配一个闲置的端口号：

 public static DatagramSocket getRandomPort() throws SocketException {  DatagramSocket s = new DatagramSocket(0);  return s; }

方法二：如果你想使用一套特定范围的端口号，最简单的办法就是依次遍历这些端口号直到有一个可用：

 public static DatagramSocket getRangePort(int[] ports) throws IOException {  for (int port : ports) {         try {             return new DatagramSocket(port);         } catch (IOException ex) {             continue; // try next port         }     }     // if the program gets here, no port in the range was found     throw new IOException("no free port found"); }

测试代码：

import java.io.IOException;import java.net.DatagramSocket;import java.net.SocketException;public class UdpPortTest { public static void main(String[] args) throws IOException {  DatagramSocket socket = getRandomPort();  System.out.println("__________socket.getLocalPort():" + socket.getLocalPort());    DatagramSocket socket2 = getRangePort(new int[] { 3843, 4584, 4843 });  System.out.println("__________socket2.getLocalPort():" + socket2.getLocalPort()); }  public static DatagramSocket getRandomPort() throws SocketException {  DatagramSocket s = new DatagramSocket(0);  return s; }  public static DatagramSocket getRangePort(int[] ports) throws IOException {  for (int port : ports) {         try {             return new DatagramSocket(port);         } catch (IOException ex) {             continue; // try next port         }     }     // if the program gets here, no port in the range was found     throw new IOException("no free port found"); } }