m11 - networking

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Module 11Core Java API: Networking

Java Course


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Module Objectives

At the end of this module, participants will beable to:

Define the basic concepts about TCP/IP

networking.

Establish a network connection.

Send data across the network.


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TCP/IP and UDP Networking

Applications that communicate over the Internet use the TCPprotocol or the UDP protocol.

TCP is a protocol that is best applicable for connections thatrequire reliability and guaranteed sequence of delivery.

UDP is a connectionless protocol. It does not care about the

sequence that the data is sent, or even if it was received at all.


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TCP/IP and UDP Networking (cont.)

9999

3333

80

Server IP: 192.168.0.1

80

Server IP: 192.168.0.2

9999

Client App

Client App

Client App

Client App

Client App

Individual nodes in anetwork are identified by

an IP address.

Network connections

created by applications

running on a singlecomputer on the network

can be further identified by

an assignedport number.

The data is transferredthrough streams.


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Establishing a Connection

For TCP connections, the URL, URLConnection, Socket, andServerSocket classes are used.

For UDP connections, the DatagramPacket, DatagramSocket,

and MulticastSocket are used.


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Using URLs

A URL is a Uniform Resource Locator and is used as areference to any resource on the Internet.

A URL is composed of aprotocol and a resource identifier.

The protocol refers to a set of rules governing the format of

messages that are exchanged between computers.

The resource identifier indicates where the resource is to be

found.

Protocol Resource Name URL

http www.accenture.com http://www.accenture.com


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Using URLs (cont.)

Create an instance representing a specific URL using the URLandURLConnection classes.

URL accentureURL = newURL ("http://www.accenture.com");

URLConnection connection = accentureURL.openConnection();

Open a stream in order to obtain that resource from thespecified URL.

BufferedReader in = newBufferedReader(newInputStreamReader(accentureURL.openStream()));


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Using URLs (cont.)

To send data to a URL resource, set the connection object to beable to send data and obtain an output stream instead.

connection.setDoOutput(t rue );

OutputStreamWriter out = newOutputStreamWriter(connection.getOutputStream());

After reading/writing to the URL, close the stream.

in.close();

out.close();

** Refer to the URLSample.java sample code


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Using Sockets

Sockets represent the end points between two applications in anetwork.

When a socket is created it is bound to an IP address and a port

number.

One end point acts as the server that waits for connections

(represented by ServerSocket class).

One or more end points acts as a client and that seeks to

connect to a server (represented by Socket class).

** Refer to the ServerSample.java and ClientSample.java sample code


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The InetAddress Class

The InetAddress class is the representation of an IP addressthat is used by the TCP and UDP protocols.

Instances of this class are returned by various factory methods:

InetAddress.getLocalHost()returns the InetAddress of the local

machine.

InetAddress.getByAddress()

returns an InetAddress based on thehost name given.

InetAddress.getByAddress(byte[])returns an InetAddress based

on the IP address passed as an array of bytes.

** Refer to the InetAddressSample.java sample code


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Creating a ServerSocket

Instantiate a ServerSocket instance and bind it to a specific portnumber.

ServerSocket server = newServerSocket(9999);

Wait for a connection from a client.

client = server.accept();

Use the returned Socket object to obtain an output or input

stream to the client.

out = newPrintWriter(client.getOutputStream(), t rue );

Close any open streams, Sockets, and ServerSockets when

finished.


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Creating a Client Socket

Instantiate an instance of the Socket class and pass the networkaddress and the port of the server the application.

Socket socket = newSocket(InetAddress.getLocalHost(), 9999);

Retrieve input or output streams bound to the socket.

BufferedReader in = newBufferedReader(newInputStreamReader(socket.getInputStream()));

Close all the streams and sockets when finished.


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Questions and Comments


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Activity

1) Create a simple chat server that will allow

multiple telnet clients to connect to your

server and chat.

2) Text entered through the telnet client

should be broadcast to all other clients

connected to the server.

3) To open a telnet client just type telnet in the console Substitute

the host and part values with whatever

you are using.

Hint: A common algorithm for the server is1) Create a ServerSocket.

2) Wait for connections.

3) For every client that connects, create a

new thread to read input from that client.

4) Go back to step 2.

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