CSC 480Software Engineering

Socket

What is Socket?

A socket is one end-point of a two-way communication link between two programs running on the network.

Socket classes are used to represent the connection between a client program and a server program. The java.net package provides two classes Socket – implement the server side of the

connection ServerSocket – that implement the client side of

the connection

The Socket Server

Normally, a server runs on a specific computer and has a socket that is bound to a specific port number.

The server just waits, listening to the socket for a client to make a connection request.

The Socket Client

The client knows the hostname of the machine on which the server is

running, and the port number to which the server is connected

To make a connection request, the client tries to rendezvous with the server on the server's machine and port.

http://java.sun.com/docs/books/tutorial/networking/sockets/index.html

Communication through Socket

Upon acceptance, the server gets a new socket bound to a different port

On the client side, if the connection is accepted, a socket is successfully created and the client can use the socket to communicate with the server

Client’s Responsibilities

Open a socket. Open an input stream and output stream to the

socket. Read from and write to the stream according to

the server's protocol. Close the streams. Close the socket.

Set up Connection

Open a socket. an input stream and output stream to the socket.

try{ aSocket = new Socket(hostName, portNumber); out = new PrintWriter(aSocket.getOutputStream(), true); in = new BufferedReader(new InputStreamReader(

aSocket.getInputStream())); } catch (IOException ex) { //error handling … }

Talk Based on Protocol

Using the out writer object to read text messages

out.println(userInput);

in.readLine();

Using the in reader object to print text messages

Clean up

Close the connection objects so that they are subject to garbage collection

out.close(); in.close(); aSocket.close();

Server’s Responsibilities

Open a ServerSocket Wait until a client request arrives

Accept the client open an input stream and output stream designated

to this client Read from and write to the stream according to

the server's protocol. Close the streams, when shutting down Close the socket.

Open a ServerSocket

Open a ServerSocket which listens to a designated port

Avoid using well-known port numbers, such as 80 for web servers

try { serverSocket = new ServerSocket(4444); } catch (IOException e) { System.out.println("Could not listen on port: 4444"); System.exit(-1); }

Accept a Client Request

Waiting for client request and accept it

Socket clientSocket = null; try { clientSocket = serverSocket.accept(); } catch (IOException e) { System.out.println("Accept failed: 4444"); System.exit(-1); }

Set up Connection to a Client

Gets the socket's input and output stream and opens readers and writers on them. To facilitate text-based communication

PrintWriter out = new PrintWriter( clientSocket.getOutputStream(), true); BufferedReader in = new BufferedReader( new InputStreamReader( clientSocket.getInputStream()));

Client-Server Communication

Design pattern: generate response by invoking the processInput method of the protocol class

// initiate conversation with client KnockKnockProtocol kkp = new KnockKnockProtocol(); outputLine = kkp.processInput(null); out.println(outputLine);

// conduct conversation with client until the finish is signaled by clientwhile ((inputLine = in.readLine()) != null) { outputLine = kkp.processInput(inputLine); out.println(outputLine); if (outputLine.equals("Bye.")) break; }

KnockKnockProtocol

This class provides All constants for this application Clues and corresponding answers The processInput method which

Reply with an answer if theInput is in the expected format Reply with the expected input

public String processInput(String theInput);

Team Formation

The whole class is divided into 3 teams Each team has

2 developers works in pair on the client app in the Windows (or RedHat Linux) environment

2 developers works in pair on the server app on Cobra

Part I – The Knock Knock App

Build up confidence Activities

Set up environment for server and client Compile and execute Add a couple of new clue-answer pairs (optional)

Part II – A Simple ATM App

Purpose: upgrade an existing client-server application to include a GUI

Code bases available A bank application with a client and a server talking

through socket A simple GUI app managing phone directory entries,

A working GUI ready for modification A method facilitating file access

The Bank Server App

The server app includes A BankServer class (with main)

A Bank class (holds an array of BankAccounts)

A BankService class (takes charge of socket communication)

A BankAccount class (facilitates balance, deposit, and withdraw)

Association – The Bank Server App

BankServer Bank

BankAccountBankService

doService()processCommand()

The Existing GUI

A list to hold names Two text fields to display

and accept a name and a number

Three buttons for clearing fields, and add and delete the current entry

A method accessing loading entries from a file

Tasks – client side

Develop a bank client with a GUI Change the List to a TextArea to display messages

from server Change the labels Name and Number to Account #

and Amount, respectively Change the button labels to Balance, Deposit, and

Withdraw, respectively; and change the control logic Write a class designated to socket connection with

the server

Tasks – server side

Modify the server so that account information can be read from a file Write a utility class which has a static method

designated for file accessing, or Write a method for BankServer to access the account

file Create a file with 10 account records

Association – The Bank Client App

BankClientMain BankClientFrame

BankClientConnector

request(String cmd):String

A Sample Screenshot

A Possible Approach

Set up environment and run the whole application

Read the existing code base Modify the client app and the server app

separatelyThe server team may take over the connector

class from the client team Integrate and test