Java Unit Viii

8/3/2019 Java Unit Viii

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Basics of network programming

IP Address

32-bit identifier

Dotted-quad: 192.118.56.25 Identifies a host

192.118.56.25


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Ports

Identifying the specific application

IP addresses identify hosts

Host has many applications Ports (16-bit identifier)

192.18.22.13

Port 80 25 23

Application WWW E-mail Telnet


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Sockets Socket is an object used for network programming.

A socket is bound to a specific port number

Network communication using Sockets is very much

similar to performing file I/O

The streams used in file I/O operation are also

applicable to socket-based I/O


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Socket Communication

A server (program) runs on a specific

computer and has a socket that is bound

to a specific port. The server waits andlistens to the socket for a client to make a

connection request.

serverClient

Connection requestport


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Contd..

If everything goes well, the server accepts theconnection. Upon acceptance, the server gets a newsocket bounds to a different port. It needs a new socket(consequently a different port number) so that it can

continue to listen to the original socket for connectionrequests while serving the connected client.

server

Client

Connection

p

ort

port port


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Client-Server communication

socket()

bind()

listen()

accept()

read()

write()

Server

block

processrequest

Client

socket()

connect()

write()

read()


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Javas .net package

Javas .net package provides two classes:

Socket for implementing a client

ServerSocket for implementing a server


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Implementing a Server1. Open the ServerSocket:

ServerSocket server;

DataOutputStream os;

DataInputStream is;

server = new ServerSocket( PORT );

2. Wait for the Client Request:

Socket s = server.accept();

3. Create I/O streams for communicating to the client

is = new DataInputStream( s.getInputStream() );

os = new DataOutputStream( s.getOutputStream() );

4. Perform communication with client

Receive from client: String line = is.readLine();

Send to client: os.write ("Hello\n");

5. Close sockets: client.close();For multithreaded server:

while(true) {

i. wait for client requests (step 2 above)

ii. create a thread with client socket as parameter (the thread creates streams (as in step(3) and does communication as stated in (4). Remove thread once service is provided.

}


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Implementing a Client

1. Create a Socket Object:client = new Socket( server, port_id );

2. Create I/O streams for communicating with the server.

is = new DataInputStream(client.getInputStream() );

os = new DataOutputStream( client.getOutputStream() );

3. Perform I/O or communication with the server: Receive data from the server:

String line = is.readLine(); Send data to the server:

os.write ("Hello\n");4. Close the socket when done:client.close();


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Simple client-serever program

A simple server (simplified code)

// SimpleServer.java:asimpleserverprogram

importjava.net.*;

importjava.io.*;

publicclassSimpleServer {

publicstaticvoidmain(Stringargs[])throws IOException {

// Registerserviceonport 1234ServerSocketserver = newServerSocket(1234);

Sockets=server.accept(); // Waitandacceptaconnection

// Getacommunicationstreamassociatedwiththesocket

OutputStreamsout = s.getOutputStream();

DataOutputStreamdos = newDataOutputStream(sout);

// Sendastring!

dos.write("Hithere");

// Closetheconnection,butnottheserversocket

dos.close();

s1out.close();

s1.close();

}

}


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A simple client (simplified code)

// SimpleClient.java:asimpleclientprogram

importjava.net.*;

importjava.io.*;

publicclassSimpleClient {

publicstaticvoidmain(Stringargs[])throws IOException {

// Open yourconnectiontoaserver,atport 1234Socketclient = newSocket(server_IP",1234);

// Getaninput filehandle fromthesocketandreadtheinput

InputStreamsIn = client.getInputStream();

DataInputStreamdis = newDataInputStream(sIn);

Stringst = newString(dis.read());

System.out.println(st);

// Whendone,justclosetheconnectionandexit

dis.close();

sIn.close();

client.close();

}

}

Java Unit Viii

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