UDP程序設計基礎技术頭條網

UDP程序設計基礎

UDP與TCP不同，基於UDP的信息傳遞更快，但是使用UDP傳遞數據的時候，用戶無法知道數據能否正確的到達主機，也並不能確定到達的目的地的順序是否和發送的順序相同，但是他快啊！！

基本模式

將數據打包(成為數據包)，然後然後將數據發往目的地。

接受別人發來的數據包，然後查看數據包

程序步驟

使用DatagramSocket()創建一個數據報套接字

使用DatagramPacket(byte[ ] buf,int offset , int length , InterAddress address , int port ),創建要發送的數據包

使用DatagramSocket類的send方法發送數據包

使用DatagramSocket( int port )創建數據報套接字，綁定到指定的端口

使用DatagramPacket(byte[ ] buf,int offset , int length)創建字節數組來接收數據包

使用DatagramPacket類的receive（）方法接受UDP包

DatagramPacket類

用來表示數據包

DatagramPacket(byte[ ] buf , int length )//指定數據包的內存空間和大小

DatagramPacket(byte[ ] buf , int length ， InterAddress address , int port)//指定數據包的內存空間和大小還制定了數據包的目的地址和端口。在發送數據時，必須指定接收方的Socket地址和端口號，因此使用這種構造函數可以創建發送數據的DataPacket對象。

DatagramSocket類

用於表示發送和接受數據包的套接字。

DatagramSocket()//構造數據報套接字並將其綁定到本地主機上任意可用的端口

DatagramSocket( int port )///創建數據報套接字並將其綁定到本地主機上指定的端口

DatagramSocket( int port ， InterAddress addr)

//創建數據報套接字並將其綁定到指定的本地地址，適用於有多個網卡和多個IP地址的情況

例題

<code>import java.net.*;

public class Weather extends Thread { 
\tString weather = "josephous handsome";
\tint port = 9898; 
\tInetAddress iaddress = null; 
\tMulticastSocket socket = null; 
\t
\tWeather() { 
\t\ttry {
\t\t\tiaddress = InetAddress.getByName("224.255.10.0");
\t\t\tsocket = new MulticastSocket(port); 
\t\t\tsocket.setTimeToLive(1); 
\t\t\tsocket.joinGroup(iaddress); 
\t\t} catch (Exception e) {
\t\t\te.printStackTrace(); 
\t\t}
\t}
\t
\tpublic void run() { 
\t\twhile (true) {
\t\t\tDatagramPacket packet = null; 
\t\t\tbyte data[] = weather.getBytes(); 
\t\t\tpacket = new DatagramPacket(data, data.length, iaddress, port);
\t\t\tSystem.out.println(new String(data)); 
\t\t\ttry {
\t\t\t\tsocket.send(packet); 
\t\t\t\tsleep(3000);
\t\t\t} catch (Exception e) {
\t\t\t\te.printStackTrace(); 
\t\t\t}
\t\t}
\t}
\tpublic static void main(String[] args) { 
\t\tWeather w = new Weather(); 
\t\tw.start(); 
\t}
}/<code>

<code>import java.awt.*;
import java.awt.event.*;
import java.net.*;

import javax.swing.*;

public class Receive extends JFrame implements Runnable, ActionListener {
\t/**
\t * 
\t */
\tprivate static final long serialVersionUID = 1L;
\tint port; 
\tInetAddress group = null; 
\tMulticastSocket socket = null; 
\tJButton ince = new JButton("開始接收");
\tJButton stop = new JButton("停止接收");
\tJTextArea inceAr = new JTextArea(10, 10);
\tJTextArea inced = new JTextArea(10, 10); 

\tThread thread; 
\tboolean b = false;
\t
\tpublic Receive() { 
\t\tsuper("廣播數據報"); 
\t\tsetDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
\t\tthread = new Thread(this);
\t\tince.addActionListener(this); 
\t\tstop.addActionListener(this); 
\t\tinceAr.setForeground(Color.blue); 
\t\tJPanel north = new JPanel(); 
\t\tnorth.add(ince); 
\t\tnorth.add(stop);
\t\tadd(north, BorderLayout.NORTH);
\t\tJPanel center = new JPanel();
\t\tcenter.setLayout(new GridLayout(1, 2));
\t\tcenter.add(inceAr); 

\t\tfinal JScrollPane scrollPane = new JScrollPane();
\t\tcenter.add(scrollPane);
\t\tscrollPane.setViewportView(inced);
\t\tadd(center, BorderLayout.CENTER); 
\t\tvalidate(); 
\t\tport = 9898;
\t\ttry {
\t\t\tgroup = InetAddress.getByName("224.255.10.0"); 
\t\t\tsocket = new MulticastSocket(port); 
\t\t\tsocket.joinGroup(group); 
\t\t} catch (Exception e) {
\t\t\te.printStackTrace(); 
\t\t}
\t\tsetBounds(100, 50, 360, 380); 
\t\tsetVisible(true); 
\t}
\t
\tpublic void run() {
\t\twhile (true) {
\t\t\tbyte data[] = new byte[1024]; 
\t\t\tDatagramPacket packet = null; 
\t\t\tpacket = new DatagramPacket(data, data.length, group, port);
\t\t\ttry {
\t\t\t\tsocket.receive(packet); 
\t\t\t\tString message = new String(packet.getData(), 0, packet
\t\t\t\t\t\t.getLength()); 
\t\t\t
\t\t\t\tinceAr.setText("正在接收的內容：\\n" + message);
\t\t\t\tinced.append(message + "\\n");
\t\t\t} catch (Exception e) {
\t\t\t\te.printStackTrace(); 

\t\t\t}
\t\t\tif (b == true) {
\t\t\t\tbreak;
\t\t\t}
\t\t}
\t}
\t
\tpublic void actionPerformed(ActionEvent e) { 
\t\tif (e.getSource() == ince) {
\t\t\tince.setBackground(Color.red); 
\t\t\tstop.setBackground(Color.yellow);
\t\t\tif (!(thread.isAlive())) { 
\t\t\t\tthread = new Thread(this); 
\t\t\t}
\t\t\tthread.start(); 
\t\t\tb = false; 
\t\t}
\t\tif (e.getSource() == stop) { 
\t\t\tince.setBackground(Color.blue); 
\t\t\tstop.setBackground(Color.red);
\t\t\tb = true; 
\t\t}
\t}
\t
\tpublic static void main(String[] args) { 
\t\tReceive rec = new Receive(); 
\t\trec.setSize(460, 200); 
\t}
}/<code>