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
