DatagramSocket 实例代码

常用类构造方法 参数传递

DatagramPacket(byte[] buf, int length); //没有地址信息的数据报构造器，用于接收端，等着接受无需指向地址，这个很好理解

DatagramPacket(byte[] buf,int length ,InetAddress address,int port);//有地址信息，用于发送端，发送到一个特定Ip上的特定端口上

DatagramSocket();//该Socket构造器无需制定端口号，用于发送端

DatagramSocket(int port);//该构造器用于接收端，绑定一个特定的本地端口.the port number can then be specified in a datagram packet destined for this socket.

void close();//

void receive(DatagramPacket p);

void send(DatagramPacket p);

void setSoTimeout(int timeout); //单位是秒，设定最长等待时间

//receiver.java
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class Receiver {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
final int MAXLEN = 100;
byte[] buffer = new byte[MAXLEN];//字符数组初始化
//byte[] buffer=new String().getBytes();//初始化字节数组
DatagramSocket ds = new DatagramSocket(2345);//接收端初始化Socket的时候一般需要绑定一个本地端口
DatagramPacket dp = new DatagramPacket(buffer,buffer.length);
//注意DS和DP的构造方法分别有两种，一种是参数里面有地址信息，一种是无地址信息，比如
//DatagramSocket 接收端需要端口信息，来绑定一个本地端口，以方便发送端制定特定的端口
//而DatagramPacket得接收端不需要地址信息，而发送端则需要地址信息，这里需要形象记忆，才能不搞混
ds.receive(dp);
int len=dp.getLength();
System.out.println(len+" bytes received.\n");
String s = new String(dp.getData(),0,len);//字节流转化为字符串的构造方法
System.out.println(dp.getAddress()+"at port"+dp.getPort()+" says:"+s);

} catch (SocketException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

}

//sender.java
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 {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
InetAddress receiveHost = InetAddress.getByName("localHost");//类静态方法

DatagramSocket theSocket = new DatagramSocket();
String message = "Hello world!";
byte[]data  = message.getBytes();
//data = theLine.getBytes();
DatagramPacket thePacket =new DatagramPacket(data,data.length,receiveHost,2345);
theSocket.send(thePacket);

} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (SocketException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

}

需要总结的几点Java小知识，

字符串转为整形函数：int receiverPort = Integer.parseInt(arg[1]);

字符串转为字节流 byte [] buffer = message.getBytes();

字节流转化为字符串 String message = new String(buffer);

字节数组初始化：byte[] buffer = new byte[MAX_SIZE];

获得数据报的相关信息，dp.getAddress();

　　　　　　　　　　　dp.getPort();

改进版本二

//MyDatagramSocket.java
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;

public class MyDatagramSocket extends DatagramSocket{
final int MAX_LEN = 100;

public MyDatagramSocket(int portNum) throws SocketException {
super(portNum);
// TODO Auto-generated constructor stub
}
public void sendMessage(InetAddress receiveHost,int receivePort,String message) throws IOException{
byte[] buffer = message.getBytes();
DatagramPacket datagram  =  new DatagramPacket(buffer,buffer.length,receiveHost,receivePort);
this.send(datagram);
}

public String receiveMessage() throws IOException{
byte[] buffer = new byte[MAX_LEN];
DatagramPacket datagram = new DatagramPacket(buffer,buffer.length);
this.receive(datagram);
String message = new String(buffer);
return message;
}

}

//ReceiverToSocket.java
import java.io.IOException;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;

public class ReceiverToSender {

/**
* @param args
* @throws IOException
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
if(args.length!=4)
System.out.println("Need four parameters!");
else{
InetAddress receiverHost = InetAddress.getByName(args[0]);
int receiverPort = Integer.parseInt(args[1]);
int myPort = Integer.parseInt(args[2]);
String message = args[3];

MyDatagramSocket mds = new MyDatagramSocket(myPort);

System.out.println(mds.receiveMessage());//不能和下一句调换，
//因为启动的时候先启动这个类，receive()方法是阻塞式的，所以会
//停留在此举，而不会发送下面的信息，另一端还未打开，所以如果现在就
//发送的话，会出现数据报丢失现象

mds.sendMessage(receiverHost, receiverPort, message);

mds.close();

}

}

}

//SenderToReceiver.java
import java.io.IOException;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;

public class SenderToReceiver {

/**
* @param args
* @throws IOException
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
if(args.length!=4)
System.out.println("Need four parameters!");
else{
InetAddress receiveHost = InetAddress.getByName(args[0]);
int receivePort = Integer.parseInt(args[1]);
int myPort= Integer.parseInt(args[2]);
String message = args[3];

MyDatagramSocket mds = new MyDatagramSocket(myPort);//此处标志自己的端口号，因为此例子是双向信息传递

mds.sendMessage(receiveHost, receivePort, message);

System.out.println(mds.receiveMessage());

mds.close();//记得关闭socket
}

}

}