Java 獲取可用 UDP 端口號的方法

Java 獲取可用 UDP 端口號的方法。TCP 獲取的辦法類似於這個。

方法一：如果你不介意獲取的端口號范圍，可以使用 DatagramSocket 的構造方法定義 0 為其端口號，系統將為其分配一個閒置的端口號：

 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圍的端口號，最簡單的辦法就是依次遍歷這些端口號直到有一個可用：

 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");
 }

測試代碼：

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");
 }
 
}

打印結果：
 __________socket.getLocalPort():2156
 __________socket2.getLocalPort():3843