[网络协议]2021-11-16

计算机网络-自顶向下 udp,tcp套接字编程 Java版

io异常处理均是throws，更应该改为try-catch形式

UDP客户服务端
udp以数据包的形式传输，而且是无连接的，所以每次传输均需指明对方端口和IP

//客户端
DatagramSocket clientSocket=new DatagramSocket(8888);//创建客户端套接字并绑定端口号
        Scanner scan=new Scanner(System.in);
        System.out.println("input lowercase sentence:");
        String str=scan.nextLine();                              //输入字符串
        byte [] bytes=str.getBytes();                            //转化为字节
        InetAddress serverIP=InetAddress.getLocalHost();         //获取服务器IP，此时为本机
        DatagramPacket sendPacket=new DatagramPacket(bytes,0,bytes.length,serverIP,6688);//将字节放入包，并写入服务器端口和IP
        clientSocket.send(sendPacket);                           //发送
        byte [] bytes1=new byte[1024];
        DatagramPacket recPacket=new DatagramPacket(bytes1,0,bytes.length); //创建包以接受服务器返回的数据
        clientSocket.receive(recPacket);                         //获取服务器返回的数据包并存放在上创建的
        String upstr=new String(recPacket.getData(),0,recPacket.getLength());//转化为字符串
        System.out.println(upstr);
        clientSocket.close();           

//服务端
DatagramSocket serverSocket=new DatagramSocket(6688);
        byte [] bytes1=new byte[1024];
        byte [] bytes2;
        DatagramPacket recpacket=new DatagramPacket(bytes1,0,bytes1.length);
        while (true){
            serverSocket.receive(recpacket);        //接受客户端发来的包
            InetAddress  clientIP=recpacket.getAddress();//从包中获取客户端的IP
            int clientPort=recpacket.getPort();//从包中获取客户端的端口
            String str=new String(recpacket.getData(),0,recpacket.getLength());
            String upstr=str.toUpperCase();
            bytes2=upstr.getBytes();
            DatagramPacket sendPacket=new DatagramPacket(bytes2,0,bytes2.length,clientIP,clientPort);
            serverSocket.send(sendPacket);

TCP客户服务端
tcp是需要建立连接的，连接建立后便可顺着连接进行全双工传输，连接建立后两个主机之间类似形成io流，可通过各自套接字获取输入，输出流。注意点是tcp服务端有一个面向所有客户的套接字用于建立连接，还有为每个客户单独分配的套接字用于传输数据

//客户端
Socket socket =new Socket(InetAddress.getLocalHost(),9898);//创建套接字绑定对方IP，端口
        OutputStream o =socket.getOutputStream();//握手过程，获取输出流
        Scanner scan=new Scanner(System.in);
        System.out.println("input lowercase sentence:");
        String str=scan.nextLine();
        o.write(str.getBytes());
        socket.shutdownOutput();
        InputStream i=socket.getInputStream();
        byte [] bytes=new byte[1024];
        int len;
        while ((len=i.read(bytes))!=-1){
             System.out.println(new String(bytes,0,len));
        }
        i.close();
        o.close();
        socket.close();              //关闭套接字

//服务端
ServerSocket serverSocket=new ServerSocket(9898);
        while (true){
        Socket newsocket=serverSocket.accept();
        InputStream inputStream=newsocket.getInputStream();
        byte[] bytes=new byte[1024];
        int len;
        while ((len=inputStream.read(bytes))!=-1){
            String  upstr=new String(bytes,0,len).toUpperCase();
            OutputStream outputStream=newsocket.getOutputStream();
            outputStream.write(upstr.getBytes());
            outputStream.close();
        }
        inputStream.close();
        newsocket.close();
        }