在 Oracle 網站上，有個簡單的 UDP 程式範例 --- Lesson: All About Datagrams，這個程式和前一個程式基本上是差不多的，差別在於，它是由
client 先送個 request 給 server 端，server 端接收到後，回應訊息給 client 端，下面是 Oracle 的範例程式。
1 package idv.steven;
2
3 import java.io.*;
4 import java.net.*;
5 import java.util.*;
6
7 public class QuoteClient {
8 public static void main(String[] args) throws IOException {
9
10 if (args.length != 1) {
11 System.out.println("Usage: java QuoteClient <hostname>");
12 return;
13 }
14
15 //get a datagram socket
16 DatagramSocket socket = new DatagramSocket();
17
18 //send request
19 byte[] buf = new byte[256];
20 InetAddress address = InetAddress.getByName(args[0]);
21 DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 4445);
22 socket.send(packet);
23
24 //get response
25 packet = new DatagramPacket(buf, buf.length);
26 socket.receive(packet);
27
28 //display response
29 String received = new String(packet.getData(), 0, packet.getLength());
30 System.out.println("Quote of the Moment: " + received);
31
32 socket.close();
33 }
34 }
client 端程式在送出 request 後，會停在第 26 行，以等待 server 端的 response。
1 package idv.steven;
2
3 import java.io.IOException;
4
5 public class QuoteServer {
6
7 public static void main(String[] args) throws IOException {
8 new QuoteServerThread().start();
9 }
10 }
1 package idv.steven;
2
3 import java.io.*;
4 import java.net.*;
5 import java.util.*;
6
7 public class QuoteServerThread extends Thread {
8
9 protected DatagramSocket socket = null;
10 protected BufferedReader in = null;
11 protected boolean moreQuotes = true;
12
13 public QuoteServerThread() throws IOException {
14 this("QuoteServerThread");
15 }
16
17 public QuoteServerThread(String name) throws IOException {
18 super(name);
19 socket = new DatagramSocket(4445);
20
21 try {
22 in = new BufferedReader(new FileReader("one-liners.txt"));
23 } catch (FileNotFoundException e) {
24 System.err.println("Could not open quote file. Serving time instead.");
25 }
26 }
27
28 public void run() {
29
30 while (moreQuotes) {
31 try {
32 byte[] buf = new byte[256];
33
34 // receive request
35 DatagramPacket packet = new DatagramPacket(buf, buf.length);
36 socket.receive(packet);
37
38 // figure out response
39 String dString = null;
40 if (in == null)
41 dString = new Date().toString();
42 else
43 dString = getNextQuote();
44
45 buf = dString.getBytes();
46
47 // send the response to the client at "address" and "port"
48 InetAddress address = packet.getAddress();
49 int port = packet.getPort();
50 packet = new DatagramPacket(buf, buf.length, address, port);
51 socket.send(packet);
52 } catch (IOException e) {
53 e.printStackTrace();
54 moreQuotes = false;
55 }
56 }
57 socket.close();
58 }
59
60 protected String getNextQuote() {
61 String returnValue = null;
62 try {
63 if ((returnValue = in.readLine()) == null) {
64 in.close();
65 moreQuotes = false;
66 returnValue = "No more quotes. Goodbye.";
67 }
68 } catch (IOException e) {
69 returnValue = "IOException occurred in server.";
70 }
71 return returnValue;
72 }
73 }
server 端程式啟動後，會先停在第 36 行以等待 request，當收到 request 後程式立即往下執行，server
端的回應內容只是由文字檔 one-liners.txt 中抓取一行文字將它回傳給 client 端。至於 client 端在那? 從程式第 48、49
行可以看到，由 client 端傳來的封包中，可以解析出 client 端的網址和 port 號，因此，server 端知道要將回應值傳向那裡。
UDP 網路程式設計 (2) --- request / response,布布扣,bubuko.com
时间： 2025-01-04 07:27:20