(七)数据报通信

• 目录

  数据报通信

  TCP和UDP的建立时间

  构造UDP的通信

  收数据报

  发数据报

  ---

UDP:非面向连接的提供不可靠的数据包式的数据传输的协议.类似于从邮局发送信件的过程

DatagramPacket,DatagramSocket,MulticastSocket等类使用UDP协议进行网络通讯

TCP:面向连接的能够提供可靠地流式数据的传输协议,类似于打电话的过程.

URL,URLConnection,Socket,ServerSocket等类都使用TCP协议进行网络通讯.

• TCP和UDP的建立时间

TCP有建立时间,UDP没有建立时间

UDP传输大小有限制:64K以内

TCP的应用:Telent,ftp

UDP的应用:ping

• 构造UDP的通信

DatagramSocket()
DatagramSocket(int port)
DatagramPacket(byte ibuf[],int ilength)//接收
DatagramPacket(byte ibuf[],int ilength,InetAddress iaddr,int iport)//发送

• 收数据报

DatagramPacket packet=new DatagramPacket(buf,256);
socket.receive(packet);

• 发数据报

​
DatagramPacket packet=new DatagramPacket(buf,buf.length,address,port);
socket.send(packet);

客户方程序:

public class QuoteClient{
public static void main(String[] args)throws IOException{
 if(args.length!=1){
System.out.println("Usage:java QuoteClient<hostname>");
 return;
}
DatagramSocket socket=new DatagramSocket();
//send request
 byte[]buf=new byte[256];
 InetAddress address=InetAddress.getByName(args[0]);
 DatagramPacket packet=new DatagramPacket(buf,buf.length,address,4445);
 Socket.send(Packet);
 //get response
 packet=new DatagramPacket(buf,buf.length);
 socket.receive(packet);
 //display responese
 String received=new String(packet.getData());
 System.out.println("Quote of the Moment:"+received);
socket.close();
  }
 }

服务器程序:

public class QuoteServer {
    public static void main(String[] args) throws java.io.IOException {
        new QuoteServerThread().start();
    }
} 

程序QuoteServerThread

public  class QuoteServerThread extends Thread {
        protected DatagramSocket socket = null;
        protected BufferedReader in = null;
        protected boolean moreQuotes = true;

        public QuoteServerThread() throws IOException {
            this("QuoteServerThread");
        }
public QuoteServerThread(String name) throws IOException {
            super(name);
            socket = new DatagramSocket(4445);
            try {
                in = new BufferedReader(new FileReader("one-liners.txt"));
            } catch (FileNotFoundException e) {
                System.err.println("Could not open quote file.Serving time instead");
            }
        }
        public void run (){
            while (moreQuotes){
                try {
                    byte[] buf = new byte[256];
                    DatagramPacket packet = new DatagramPacket(buf, buf.length);
                    socket.receive(packet);
                    String dString=null;
                    if (in==null)
                    dString=new Date().toString();
 else dString=getNextQuote();
                     buf = dString.getBytes();
                     //发送响应客户端的地址和端口号
                    InetAddress address = packet.getAddress();
                    int port = packet.getPort();
                    packet = new DatagramPacket(buf, buf.length, address, port);
                    socket.send(packet);
                }catch (IOException e){
                    e.printStackTrace();
                    moreQuotes=false;
                }
            }
socket.close();
        }
protected String getNextQuote(){
    String returnValue=null;
    try{
        if((returnValue=in.readLine())==null){
            in.close();
            moreQuotes=false;
            returnValue="No more quotes.Goodbye.";
        }
        
        
        }catch(IOException e){
        returnValue="IOException occurred in server";
        }
        return returnValue;
        }
        }
    }