// This is a java program to display the use of the java.net.Socket class

import java.io.BufferedInputStream;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.IOException;

import java.nio.charset.StandardCharsets;

// import java server socket

import java.net.ServerSocket;

// import java client socket

import java.net.Socket;

/**

* Example using sockets Client/Server

*/

public class SocketExample {

public static void main(String[] args) {

SocketServerExample server = new SocketServerExample(); // Aways need new intance to use in static context

SocketClientExample client = new SocketClientExample(); // Aways need new instance to use in static context

// Run server in a new Thread.

new Thread(() -> server.startServer(9191)).start(); // Lambda expression to instantiate new Thread

// Run cliente

client.runClient("127.0.0.1", 9191);

}

}

/**

* SocketServer example class

* This example consists in one Socket Server to be a road of data

* and two Socket Clients, one for send data between socket server and other to recive this data.

*/

class SocketServerExample {

public void startServer(int port) { // method startServer recive int port value

try {

//Start the server in informed port and wait for connection to initiate

ServerSocket server = new ServerSocket(port);

System.out.println("Server Started. Waiting for connection ...");

// Accept new cliente connection

Socket socket = server.accept();

System.out.println("Got connection from client.");

//Get input stream from socket variable and convert the same to DataInputStream

DataInputStream in = new DataInputStream(new BufferedInputStream(socket.getInputStream()));

//Read type and length of data transmited

char dataType = in.readChar();

int length = in.readInt();

System.out.println("Type : "+ dataType);

System.out.println("Lenght :"+ length);

if(dataType == 's') { // 's' is a String

//Read String data in bytes

byte[] messageByte = new byte[length];

boolean end = false;

StringBuilder dataString = new StringBuilder(length); // Initiate StringBuild with pre aloccated size of length

int totalBytesRead = 0;

//We need to run while loop, to read all data in that stream

while(!end) {

// read byte

int currentBytesRead = in.read(messageByte);

// Add add to counter

totalBytesRead = currentBytesRead + totalBytesRead;

if(totalBytesRead <= length) { // have more bytes in message?

// yes add final byte

dataString.append(new String(messageByte,0,currentBytesRead,StandardCharsets.UTF_8));

} else {

// no, add byte to dataString

dataString.append(new String(messageByte,0,length - totalBytesRead + currentBytesRead,StandardCharsets.UTF_8));

}

// Verify end of messsage.

if(dataString.length()>=length) {

end = true;

}

}

// Show content of bytes recieved

System.out.println("Read "+length+" bytes of message from client. Message = "+dataString);

}

} catch (Exception e) {

e.printStackTrace();

}

}

}

/**

* Client Socket class to sending data in TLV format.

*/

class SocketClientExample {

public void runClient(String ip, int port) {

try {

// New Socket client

Socket socket = new Socket(ip, port);

System.out.println("Connected to server ...");

// Instance of DataStream in/out

DataInputStream in = new DataInputStream(System.in);

DataOutputStream out = new DataOutputStream(socket.getOutputStream());

char type = 's'; // s for string

String data = "This is a string of length 29";

int length = data.length(); // length of pack to send

// Convert String to bytes to transmit

// Charset is importante to reciver

byte[] dataInBytes = data.getBytes(StandardCharsets.UTF_8);

//Sending data in TLV format

//TLV (type-length-value) is an encoding scheme used for optional information element in a certain protocol.

out.writeChar(type);

out.writeInt(length);

out.write(dataInBytes);

} catch (IOException e) {

e.printStackTrace();

}

}

}