Java--scoket Communications

Socket

The two programs on the network realize the exchange of data through a two-way communication connection, one end of this connection is called a socket.

Sockets are the abstraction layer of TCP/IP Protocol communication, so we also need to understand the TCP protocol

Transport Layer Protocol

1. TCP: Connection-oriented, experienced three handshake, the advantage is reliable transmission (to ensure data correctness, ensure the order of data), for the transmission of large amounts of data (stream mode), the disadvantage is that slow, the establishment of a connection requires more overhead time and system resources.

2. UDP: For non-connected, transport unreliable drops (data loss), for transmitting small amounts of data (packet mode), fast.

Add: The so-called three-time handshake (Three-way handshake), which is when a TCP connection is established, requires a total of 3 packets sent by the client and the server.

The purpose of the three-time handshake is to connect the server to the specified port, establish a TCP connection, and synchronize the serial number and confirmation number of both parties and Exchange TCP window size information. In socket programming, the client executes connect (). Will trigger a three-time handshake.

Let's implement the following server-to-client communication:

Server: Server.class

Package sc_test;

Import Java.io.BufferedWriter;

Import Java.io.DataOutputStream;

Import java.io.IOException;

Import Java.io.OutputStreamWriter;

Import Java.net.ServerSocket;

Import Java.net.Socket;

public class Server {

public static void Main (string[] args) throws IOException {

ServerSocket Server =new serversocket (8888); Create a server-specific port

System.out.println ("The server has been created waiting for the client ... ");

Socket socket =server.accept (); receiving connections from clients

System.out.println (" a client establishes a connection ");

Send Data

String msg = " Welcome connection Server ";

output Stream

Output Method One

BufferedWriter bwriter = new BufferedWriter (New OutputStreamWriter (Socket.getoutputstream ()));

//

Bwriter.write (msg);

Bwriter.newline ();

Bwriter.flush ();

Output Method Two

DataOutputStream dos = new DataOutputStream (Socket.getoutputstream ());

Dos.writeutf (msg);

Dos.flush ();

}

}

Client: Client.class

Package sc_test;

Import Java.io.BufferedReader;

import Java.io.DataInputStream;

import java.io.IOException;

Import Java.io.InputStreamReader;

import Java.net.Socket;

import java.net.UnknownHostException;

Public class Client {

Public Static void Main (string[] args) throws Unknownhostexception, IOException {

Socket Client = new socket ("localhost", 8888); To create a client, you must specify a server + port to establish a connection

Receive Data

BufferedReader br= new BufferedReader (New InputStreamReader (Client.getinputstream ()));

String echo = Br.readline (); Blocking Method

the corresponding method two

DataInputStream dis = new datainputstream (Client.getinputstream ());

String echo = Dis.readutf ();

System. out. println (ECHO);

}

}

Experimental results:

Open the server thread, the following occurs, into the blocking state, waiting for the client to connect as follows:

The server has been created waiting for the client ...

Then run the client program and receive the following information sent to the client by the server:

Welcome to connect to server

The server receives the printing information as follows:

The server has been created waiting for the client ...
A client establishes a connection

Java--scoket Communications