Download - Networking in java
Networking
Shravan Upadhayay
Shravan Upadhayay
Introduction
Java.net package provides support for networking.
What makes Java a good language for networking are the classes defined in the java.net package.
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Concept of Networking
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Sockets
Socket is the name given , in one particular programming model, to the end points of a communication link between processes.
When processes communicate over a network, Java Technology uses streams model.
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Sockets
Sockets: Sockets hold two streams: an input
stream and an output stream. Each end of the socket has a pair of
streams.
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Socket A process send data to another process
through a network by writing to the output stream associated with the Socket.
A process reads data written by another process by reading from the input stream associated with the Socket.
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Setting Up the Connection To setup the network connection, one
machine must run a program that is waiting for a connection, and a second machine must try to reach the first.
Set up of a network connection is similar to a telephone system: One end must dial the other end, which must be listening.
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Networking
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Addressing the Connection
When you make a network connection, you need to know the address or the name of the remote machine.
In addition, a network connection, requires a port number, which you can think of as a telephone extension number.
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Port Numbers Port numbers in TCP/IP systems are
16-bit numbers and the values range from 0-65535. Port numbers below 1024 are reserved
for predefined services. Client port numbers are allocated by the
host OS to something not in use, while server port numbers are specified by the programmer, and are used to identify a particular service.
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Both client and server must agree in advance on which port to use.
If the port numbers used by the two parts of the system do not agree, communication does not occur.
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Server
A server is anything that has some resource that can be shared. There are compute servers, which
provide computing power; print servers, which manage a collection
of printers; disk servers, which provide networked
disk space; and web servers, which store web pages.
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Client
A client is simply any other entity that wants to gain access to a particular server.
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The notion of a socket allows a single computer to serve many different clients at once, as well as serving many different types of information.
This feat is managed by the introduction of a port, which is a numbered socket on a particular machine.
A server process is said to "listen" to a port until a client connects to it. A server is allowed to accept multiple clients connected to the same port number, although each session is unique.
To manage multiple client connections, a server process must be multithreaded or have some other means of multiplexing the simultaneous I/O.
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Local Host Info// Demonstrate InetAddress.import java.net.*;class InetAddressTest{public static void main(String args[]) throwsUnknownHostException{InetAddress Address = InetAddress.getLocalHost();System.out.println(Address.getHostName());System.out.println(Address.getHostAddress());}}
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TCP/IP TCP/IP sockets are used to implement
reliable, bidirectional, persistent, point-to- point, stream-based connections between hosts on the
Internet. A socket can be used to connect Java's I/O
system to other programs that may reside either on the local machine or on any other machine on the Internet.
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There are two kinds of TCP sockets in Java. One is for servers, and the other is for
clients. The ServerSocket class is designed to be
a "listener," which waits for clients to connect before doing anything.
The Socket class is designed to connect to server sockets and initiate protocol exchanges.
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The creation of a Socket object implicitly establishes a connection between the client and server.
There are no methods or constructors that explicitly expose the details of establishing that connection.
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Here are two constructors used to create client sockets: Socket(String hostName, int port) Creates a socket connecting the local host to the
named host and port; can throw an UnknownHostException or an IOException.
Socket(InetAddress ipAddress, int port) Creates a socket using a preexisting
InetAddress object and a port; can throw an IOException.
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A socket can be examined at any time for the address and port information associated with it, by use of the following methods: InetAddress getInetAddress( )
Returns the InetAddress associated with the Socket object. int getPort( )
Returns the remote port to which this Socket object is connected. int getLocalPort( )
Returns the local port to which this Socket object is connected.
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Once the Socket object has been created, it can also be examined to gain access to the input and output streams associated with it.
Each of these methods can throw an IOException if the sockets have been invalidated by a loss of connection on the Net.
These streams are used exactly like the I/O streams receive data.
InputStream getInputStream( ) Returns the InputStream
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InputStream getInputStream( ) Returns the InputStream associated
with the invoking socket. OutputStream getOutputStream() Returns the OutputStream
associated with the invoking socket. void close() Closes both the InputStream and
OutputStream.
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Socket functional calls socket (): Create a socket bind(): bind a socket to a local IP address and port # listen(): passively waiting for connections connect(): initiating connection to another socket accept(): accept a new connection Write(): write data to a socket Read(): read data from a socket close(): close a socket (tear down the connection)
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Socket-programming using TCPTCP service: reliable byte stream transfer
process
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variables
socket
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variables
socket
internet
clientserversocket( )
bind( )connect( )
socket( )bind( )listen( )
accept( )send( )
recv( )
close( ) close( )
recv( )send( )
TCP conn. request
TCP ACK
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Socket programming with TCP
Example client-server app: client reads line from
standard input (inFromUser stream) , sends to server via socket (outToServer stream)
server reads line from socket
server converts line to uppercase, sends back to client
client reads, prints modified line from socket (inFromServer stream)
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Process
clientSocket
inputstream
inputstream
outputstream
TCPsocket
Input stream: sequence of bytesinto process
output stream: sequence of bytes out of process
Clientprocess
client TCP socket
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Client/server socket interaction: TCP
wait for incomingconnection requestconnectionSocket =welcomeSocket.accept()
create socket,port=x, forincoming request:welcomeSocket =
ServerSocket()
create socket,connect to hostid, port=xclientSocket =
Socket()
closeconnectionSocket
read reply fromclientSocket
closeclientSocket
Server (running on hostid) Client
send request usingclientSocketread request from
connectionSocket
write reply toconnectionSocket
TCP connection setup
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TCPClient.javaimport java.io.*; import java.net.*;
class TCPClient { public static void main(String argv[]) throws Exception{ String sentence; String modifiedSentence;
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("hostname", 6789);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
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TCPClient.javaBufferedReader inFromServer =
new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + '\n');
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
clientSocket.close(); }
}
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TCPServer.javaimport java.io.*; import java.net.*; class TCPServer { public static void main(String argv[]) throws Exception
{ String clientSentence; String capitalizedSentence;
ServerSocket welcomeSocket = new
ServerSocket(6789);
while(true) {
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new
InputStreamReader(connectionSocket.getInputStream()));
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TCPServer.java
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
capitalizedSentence = clientSentence.toUpperCase() + '\n';
outToClient.writeBytes(capitalizedSentence); } }
}