Java Programming TCP IP Server and Client

What is TCP/IP?

TCP/IP ( Transmission Control Protocol/Internet Protocol ) is a suite of communication protocols used to interconnect network devices on the internet.

How to implement TCP/IP in java program?

  • Java has a different socket class that must be used for creating server applications.
  • ServerSocket class is used to create servers that listen for either local or remote client programs to connect to them on published ports.

ServerSocket Class

ServerSocket is quite different from normal socket. When creating a ServerSocket, it will register itself with the system having an interest in client connections.

ServerSocket Constructors

Constructors might throw an IOException under adverse conditions. Below are the different constructor types for ServerSocket Class.
ServerSocket(int port)
Creates a server socket on the specified port and queue length of 50.
ServerSocket(int port, int maxQueue)
Creates a server socket on the specified port with a maximum queue length (maxQueue).
ServerSocket(int port, int maxQueue, InetAddress address)
Creates a server socket on the specified port with a maximum queue length on a specified host address.

TCP/IP Server Java program

// TCP/IP Server Program                                                        
import java.io.*;                                                               
import java.net.*;                                                              
                                                                                
class Server                                                                    
{                                                                               
   public static void main(String args[])throws Exception                       
   {                                                                            
        try                                                                     
        {                                                                       
                String line, newLine;                                           
                ServerSocket ss=new ServerSocket(6789);                         
                // Communication Endpoint for the client and server.            
                while(true)                                                     
                {                                                               
                  // Waiting for socket connection                              
                  Socket s=ss.accept();                                         
                  System.out.println("Server Started...");                      
                  // DataInputStream to read data from input stream             
                  DataInputStream inp=new DataInputStream(s.getInputStream());  
                  // DataOutputStream to write data on outut stream             
                  DataOutputStream out = new DataOutputStream(s.getOutputStream());
                  DataInputStream in=new DataInputStream(System.in);            
                  // Rads a line text                                           
                  while(true) {                                                 
                   System.out.println("Press 'q' if you want to exit server");  
                   line = inp.readLine();                                       
                   // Writes in output stream as bytes                          
                   //out.writeBytes(line +'\n');                                  
                   System.out.println("Received from client: " + line);         
                   newLine = in.readLine();                                     
                   if (newLine.equals("q")) {                                   
                    out.writeBytes("Server is down..." +'\n');                  
                    return;                                                     
                   } else {                                                     
                     out.writeBytes(newLine + '\n');                            
                   }                                                            
                  }                                                             
                }                                                               
        }                                                                       
        catch(Exception e)                                                      
        {                                                                       
                                                                                
        }                                                                       
   }                                                                            
}  

TCP/IP Client Java program

// TCP/IP Client program                                                        
import java.io.*;                                                               
import java.net.*;                                                              
class Client                                                                    
{                                                                               
        public static void main(String args[])throws Exception                  
        {                                                                       
                String line, newLine;                                           
                try                                                             
                {                                                               
                        DataInputStream in=new DataInputStream(System.in);      
                        // Communication Endpoint for client and server         
                        Socket cs=new Socket("LocalHost",6789);                 
                        System.out.println("Client Started...");          
                        // DataInputStream to read data from input stream       
                        DataInputStream inp=new DataInputStream (cs.getInputStream());
                        // DataOutputStream to write data on outut stream   
                        DataOutputStream out=new DataOutputStream(cs.getOutputStream());
                        while(true) {                                           
                         newLine = in.readLine();                               
                         if (newLine.equals("q")) {                             
                            out.writeBytes("Client is down..." +'\n');          
                            return;                                             
                         } else {                                               
                           out.writeBytes(newLine + '\n');                      
                         }                                                      
                         line = inp.readLine();                                 
                         System.out.println("Received from server: "+line);     
                        }                                                       
                }                                                               
                catch(Exception e)                                              
                {                                                               
                }                                                               
        }                                                                       
}     
Server Output:
// Compile and Run server program first
$ javac Server.java 
Note: Server.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
$ java Server
Server Started...
Press 'q' if you want to exit server
Received from client: hi
how are you?
Press 'q' if you want to exit server
Received from client: i am fine, how is going
q
Client Output:
// Compile and Run client program when server program is running
$ javac Client.java 
Note: Client.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
$ java Client
Client Started...
hi
Received from server: how are you?
i am fine, how is going
Received from server: Server is down...

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