[Dark horse programmer Java training and Android training] network programming video learning

/*
Requirement: establish communication between computers through the network.
Steps:
1. First, find the computer of the other party through the IP address,
2. Find the application to receive through the port number,
3. Finally, you can establish communication.
*/

1. Basic network programming knowledge
Local Loop IP Address: 127.0.0.1;
The port number ranges from 0 ~ 65535,0 ~ 1023 used for well-known network services and applications;
TCP: Transmission Control Protocol, connection-oriented reliable and error-free communication protocol;
UDP: user data packet protocol, non-connection, unguaranteed communication protocol, fast speed
Data frame format: [protocol type | source IP address | destination IP address | source port | destination port | frame number | frame data]

2. Socket data transmission process
The application generates a socket;
Use a program to send socket information to the driver;
The application sends data to the socket;
The driver extracts data from the socket and sends it through the NIC.

3. Socket data receiving process
The application generates a socket;
The application sends the socket information to the driver;
The driver transmits data packets sent from the NIC to the corresponding socket;
The application extracts data from the socket.

4. datagramsocket class
Three constructors;
Close () method, send (datagrampacketp), receive (datagrampacket P)
 
5. datagrampacket class
Two constructors;
Getinetaddress (), getport ();
Getdata (), getlength ()

6. inetaddress class
Getbyname ();
Gethostaddress ();

7. simple UDP Program

Import java.net .*;
Class udpsendtest
{
Public static void main (string [] ARGs)
{
Try
{
Datagramsocket DST = new datagramsocket ();
DST. Send (New datagrampacket ("A". getbytes (), "A". getbytes (). length, inetaddress. getbyname ("192.168.1.100"), 3000 ));
DST. Close ();
}
Catch (Exception e)
{
}
}
}

Import java.net .*;
Class UDPRecvTest
{
Public static void main (String [] args)
{
Try
{
DatagramSocket dst = new DatagramSocket (3000 );
Byte [] buf = new byte [1, 1024];
DatagramPacket dpt = new DatagramPacket (buf, 1024 );
Dst. receive (dpt );
System. out. println (new String (dpt. getData (), 0, dpt. getLength ()));
}
Catch (Exception e)
{
}
}
}

8. Interaction between the TCP client and the TCP Server
The server program creates a ServerSocket and calls accept () to wait for the client to connect;
The client creates a Socket and requests to connect to the server;
The server receives client connection requests and creates a new Socket;
The two sockets that have established the connection are in a separate thread.

9. ServerSocket
Four Constructors
Close () method and accept () method

10. Socket
Five Constructors
GetInputStream () method and getOutputStream () method

11. Simple Tcp Program

Import java.net .*;
Import java. io .*;
Class TcpServer
{
Public static void main (String [] args)
{
Try
{
ServerSocket ss = new ServerSocket (8001 );
Socket s = ss. accept ();
InputStream ips = s. getInputStream ();
OutputStream ops = s. getOutputStream ();
Ops. write ("Hello World". getBytes ());
BufferedReader br = new BufferedReader (new InputStreamReader (ips ));
System. out. println (br. readLine ());

Br. close ();
Ops. close ();
S. close ();
Ss. close ();
}
Catch (Exception e)
{
E. printStackTrace ();
}
}
}