网络编程之UDP程序数据包的发送

public DatagramPacket
(byte[] buf, int length)  用来就收数据包的大小

public DatagramPacket
(byte[] buf,  int length,  InetAddress
address,  int port) 用来指定数据包发送的大小和目的主机的地址和端口，

总结：一个是用来接受数据包，一个是用来发送数据包

普通方法：

public InetAddress
getAddress
() 获得发送方的IP地址

public byte[] getData
() 获得就收数据包的缓冲区大小

public int getLength
() 获得实际数据包的长度

InetAddress类：可以理解java为IP封装的类

其中有个方法常用：

public static InetAddress
getByName
(String
host) 给定主机名返回IP地址

实例程序代码：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
public class Sender {
public static void main(String[] args) {
try {
DatagramSocket ds = new DatagramSocket();
byte[] buf = new byte[1024];
DatagramPacket dp = new DatagramPacket("www.csdn.net".getBytes(), "www.csdn.net".length(), InetAddress.getByName("127.0.0.1"), 3000);
ds.send(dp);
ds.close();
} catch (SocketException e) {
e.printStackTrace();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

package cn.itcast.socket.udp;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
public class Receiver {
public static void main(String[] args) {
try {
DatagramSocket ds = new DatagramSocket(3000);
byte[] buf = new byte[1024];
DatagramPacket dp = new DatagramPacket(buf, buf.length);
ds.receive(dp);
System.out.println(dp.getData().length);
System.out.println(dp.getSocketAddress());
System.out.println(ds.getInetAddress());
String data = " form :" + dp.getAddress().getHostAddress() + new String(dp.getData(), 0, dp.getLength());
System.out.println(data);
} catch (SocketException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}