关于Java的UDP通信连接实现

知识点：

1.关于TCP与UDP的主要区别：

TCP—传输控制协议,提供的是面向连接、可靠的字节流服务。当客户和服务器彼此交换数据前，必须先在双方之间建立一个TCP连接，之后才能传输数据。TCP提供超时重发，丢弃重复数据，检验数据，流量控制等功能，保证数据能从一端传到另一端。

UDP—用户数据报协议，是一个简单的面向数据报的运输层协议。UDP不提供可靠性，它只是把应用程序传给IP层的数据报发送出去，但是并不能保证它们能到达目的地。由于UDP在传输数据报前不用在客户和服务器之间建立一个连接，且没有超时重发等机制，故而传输速度很快.

2.关于InetAddress的用法：

IP地址是IP使用的32位（IPv4）或者128位（IPv6）位无符号数字，它是传输层协议TCP，UDP的基础。InetAddress是Java 对IP地址的封装，在java.net中有许多类都使用到了InetAddress，包括 ServerSocket，Socket，DatagramSocket等等。

InetAddress的实例对象包含以数字形式保存的 IP地址，同时还可能包含主机名（如果使用主机名来获取InetAddress的实例，或者使用数字来构造，并且启用了反向主机名解析的功能）。 InetAddress类提供了将主机名解析为IP地址（或反之）的方法。

InetAddress对域名进行解析是使用本地机器配置或者网络命名服务（如域名系统（Domain Name System，DNS）和网络信息服务（Network Information Service，NIS））来实现。对于DNS来说，本地需要向DNS服务器发送查询的请求，然后服务器根据一系列的操作，返回对应的IP地址，为了提高效率，通常本地会缓存一些主机名与IP地址的映射，这样访问相同的地址，就不需要重复发送DNS请求了。在java.net.InetAddress类同样采用了这种策略。在默认情况下，会缓存一段有限时间的映射，对于主机名解析不成功的结果，会缓存非常短的时间（10秒）来提高性能。

3.Java中的DatagramPacket与DatagramSocket的初步

DatagramPacket表示存放数据的数据报，DatagramSocket表示接受或发送数据报的套接字

代码实现

1.构建UDP服务器

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package udp;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

/**
*
* @author Administrator
*/
public class EchoUDPServer {
private int port=6666;
private DatagramSocket socket;
public EchoUDPServer() throws IOException{
socket =new DatagramSocket(port);
System.out.println("UDP服务器已启动.....");
}
public String echo(String msg){
return "server ："+msg;
}
public void service(){
while(true){
try{
DatagramPacket packet =new DatagramPacket(new byte[512],512);
socket.receive(packet);
String msg = new String(packet.getData(),0,packet.getLength(),"GB2312");
System.out.println(packet.getAddress()+" : "+packet.getPort()+">"+msg);
packet.setData(echo(msg).getBytes("GB2312"));
socket.send(packet);
}catch(IOException e){
System.out.println(e);
}
}
}
public static void main(String args[])throws IOException{
new EchoUDPServer().service();
}
}

2.UDP客户端

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package udp;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

/**
*
* @author Administrator
*/
public class EchoUDPClient {
private int       remotePort;
private InetAddress remoteIP;

private DatagramSocket socket; //UDP套接字

public EchoUDPClient(String ip,String port)throws IOException{
this.remotePort=Integer.parseInt(port);
this.remoteIP=InetAddress.getByName(ip);

//创建一个UDP套接字，与本地任意一个未使用的UDP端口绑定
socket=new DatagramSocket();
//与本地一个固定的UDP端口绑定
//   socket=new DatagramSocket(9000);
}

//定义一个数据的发送方法。
public void send(String msg){
try {
//先准备一个待发送的数据报
byte[] outputData=msg.getBytes("GB2312");
//构建一个数据报文。
DatagramPacket outputPacket=new DatagramPacket(outputData,
outputData.length,remoteIP,remotePort);
//给EchoUDPServer发送数据报
socket.send(outputPacket);  //给EchoUDPServer发送数据报
} catch (IOException ex) { }
}

//定义一个数据的接收方法。
public String receive(){//throws IOException{
String msg;
//先准备一个空数据报文
DatagramPacket inputPacket=new DatagramPacket(new byte[512],512);
try {
//阻塞语句，有数据就装包，以装完或装满为此.
socket.receive(inputPacket);
//从报文中取出字节数据并装饰成字符。
msg=new String(inputPacket.getData(),
0,inputPacket.getLength(),"GB2312");
} catch (IOException ex) {
msg=null;
}
return msg;
}

public void close(){
if(socket!=null)
socket.close();//释放本地端口.
}
}

3.用户界面

代码：

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package udp;

import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
*
* @author Administrator
*/
public class EchoUDPClinetFrame extends javax.swing.JFrame {
private EchoUDPClient ec;
private String msg;
/**
* Creates new form IOJFrame
*/
public EchoUDPClinetFrame() throws IOException {
initComponents();
}

/**
* This method is called from within the constructor to initialize the form.
* WARNING: Do NOT modify this code. The content of this method is always
* regenerated by the Form Editor.
*/
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

jLabel1 = new javax.swing.JLabel();
jTextField1 = new javax.swing.JTextField();
jLabel2 = new javax.swing.JLabel();
jTextField2 = new javax.swing.JTextField();
jButton2 = new javax.swing.JButton();
jScrollPane1 = new javax.swing.JScrollPane();
jTextArea1 = new javax.swing.JTextArea();
jLabel3 = new javax.swing.JLabel();
jLabel4 = new javax.swing.JLabel();
jScrollPane2 = new javax.swing.JScrollPane();
jTextArea2 = new javax.swing.JTextArea();
jButton3 = new javax.swing.JButton();
jButton4 = new javax.swing.JButton();

setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

jLabel1.setText("IP地址");

jTextField1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jTextField1ActionPerformed(evt);
}
});

jLabel2.setText("端口");

jTextField2.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jTextField2ActionPerformed(evt);
}
});

jButton2.setText("连接");
jButton2.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton2ActionPerformed(evt);
}
});

jTextArea1.setEditable(false);
jTextArea1.setColumns(20);
jTextArea1.setRows(5);
jTextArea1.addCaretListener(new javax.swing.event.CaretListener() {
public void caretUpdate(javax.swing.event.CaretEvent evt) {
jTextArea1CaretUpdate(evt);
}
});
jTextArea1.addAncestorListener(new javax.swing.event.AncestorListener() {
public void ancestorMoved(javax.swing.event.AncestorEvent evt) {
}
public void ancestorAdded(javax.swing.event.AncestorEvent evt) {
jTextArea1AncestorAdded(evt);
}
public void ancestorRemoved(javax.swing.event.AncestorEvent evt) {
}
});
jScrollPane1.setViewportView(jTextArea1);

jLabel3.setText("信息显示区");

jLabel4.setText("信息录入区");

jScrollPane2.setAutoscrolls(true);

jTextArea2.setColumns(20);
jTextArea2.setRows(5);
jTextArea2.setAutoscrolls(false);
jScrollPane2.setViewportView(jTextArea2);

jButton3.setText("发送");
jButton3.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton3ActionPerformed(evt);
}
});

jButton4.setText("退出");

javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jLabel1)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 121, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(18, 18, 18)
.addComponent(jLabel2)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, 63, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jButton2, javax.swing.GroupLayout.PREFERRED_SIZE, 83, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 467, Short.MAX_VALUE)
.addComponent(jLabel3)
.addComponent(jLabel4)
.addComponent(jScrollPane2))
.addGap(0, 0, Short.MAX_VALUE))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addGap(0, 0, Short.MAX_VALUE)
.addComponent(jButton3)
.addGap(38, 38, 38)
.addComponent(jButton4)))
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel1)
.addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel2)
.addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jButton2))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jLabel3)
.addGap(8, 8, 8)
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 154, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(18, 18, 18)
.addComponent(jLabel4)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jScrollPane2, javax.swing.GroupLayout.PREFERRED_SIZE, 21, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 27, Short.MAX_VALUE)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jButton3)
.addComponent(jButton4))
.addGap(22, 22, 22))
);

pack();
}// </editor-fold>

private void jTextField2ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}

private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}

private void jButton3ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
//发送按钮
msg=jTextArea2.getText();
jTextArea1.append("已发送 : "+msg+"\n");
jTextArea2.setText(null);
try {
ec.send(msg);//发送一串字符。
} catch (Exception ex) {
Logger.getLogger(EchoUDPClinetFrame.class.getName()).log(Level.SEVERE, null, ex);
}
}

private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
//连接按钮
String ip;
String port;
if(!jTextField1.getText().equals("")){
ip=jTextField1.getText();
port=jTextField2.getText();
}
else{
ip = "222.201.101.15";
port = "6666";
}
try {
ec=new EchoUDPClient(ip,port);
jTextArea1.append("UDP创建成功.\r\n");
Thread receiver = new Thread(){
@Override
public void run(){
String msg = null;
while(true){
try{
msg = ec.receive();
} catch(Exception ex){
jTextArea1.append("套接字异常关闭"+"\n");
}
if(msg!=null){
jTextArea1.append(msg+"\n");
}
else{
jTextArea1.append("你的对话已关闭！"+"\n");
break;
}
}
}};
receiver.start();
} catch (IOException ex) {
jTextArea1.append("UDP创建失败.\r\n");
}

}

private void jTextArea1CaretUpdate(javax.swing.event.CaretEvent evt) {
// TODO add your handling code her
}

private void jTextArea1AncestorAdded(javax.swing.event.AncestorEvent evt) {
// TODO add your handling code here:
}

/**
* @param args the command line arguments
*/
public static void main(String args[]) throws IOException {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html */
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(EchoUDPClinetFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(EchoUDPClinetFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(EchoUDPClinetFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(EchoUDPClinetFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
EchoUDPClinetFrame ioj =new EchoUDPClinetFrame();
ioj.setVisible(true);

} catch (IOException ex) {
Logger.getLogger(EchoUDPClinetFrame.class.getName()).log(Level.SEVERE, null, ex);
}
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton jButton2;
private javax.swing.JButton jButton3;
private javax.swing.JButton jButton4;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JScrollPane jScrollPane2;
private javax.swing.JTextArea jTextArea1;
private javax.swing.JTextArea jTextArea2;
private javax.swing.JTextField jTextField1;
private javax.swing.JTextField jTextField2;
// End of variables declaration
}