Advance Computer Programming Networking Basics – explores the java.net package which provides support for networking. – Also Called “programming for the Internet” – Java.net Package is basically a collection of Networking classes – These networking classes encapsulate the “socket” paradigm.

Advance Computer Programming – The networking support first found in 4.2 BSD eventually became the de facto standard for the Internet – TCP/IP remains the primary standard for communications within the Internet

Advance Computer Programming Socket Overview – A network socket is a lot like an electrical socket – Think how your electric bill is created e.g. – Sockets are simply the end-points of a connection between two devices – In fact, the Socket has no idea what’s coming it just sees a stream of bytes – When the server gets the bytes, it’s up to your server code to figure out what those bytes are supposed to mean

Advance Computer Programming – The same idea applies to network sockets, except we talk about TCP/IP packets and IP addresses rather than electrons and street addresses – Internet Protocol (IP) is a low-level routing protocol that breaks data into small packets and sends them to an address across a network but no guarantee to deliver said packets – Transmission Control Protocol (TCP) is a higher- level protocol that manages to robustly string together these packets

– sorting and retransmitting them as necessary to reliably transmit your data – A third protocol, User Datagram Protocol (UDP), sits next to TCP and can be used directly to support fast, connectionless, unreliable transport of packets.

Advance Computer Programming Client / Server – It seems complicated when you read about it in corporate marketing statements but it is actually quite simple. – 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; web servers, which store web pages.

Advance Computer Programming – A client is simply any other entity that wants to gain access to a particular server. – The interaction between client and server is just like the interaction between a lamp and an electrical socket. – The power grid of the house is the server, and the lamp is a power client. – The server is a permanently available resource, while the client is free to “unplug” after it is has been served

Advance Computer Programming – In Berkeley sockets, 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.

Advance Computer Programming Reserved Sockets – TCP/IP reserves the lower 1,024 ports for specific protocols – if you have spent any time surfing the Internet. Port number 21 is for FTP 23 is for Telnet 25 is for 79 is for finger 80 is for HTTP 119 is for netnews

Advance Computer Programming – Here’s an example of a client requesting a single file, /index.html, and the server replying that it has successfully found the file and is sending it to the client:

Advance Computer Programming Proxy Servers – A proxy server speaks the client side of a protocol to another server – This is often required when clients have certain restrictions on which servers they can connect to. – A proxy server has the additional ability to filter certain requests or cache the results of those requests for future use. – When a popular web site is being hit by hundreds of users, a proxy server can get the contents of the web server’s popular pages once, saving expensive internetwork transfers while providing faster access to those pages to the clients.

Advance Computer Programming Internet Addressing – Every computer on the Internet has an address. – An Internet address is a number that uniquely identifies each computer on the Net. – all Internet addresses consisted of 32-bit values. – This address type was specified by IPv4 (Internet Protocol, version 4) – However, a new addressing scheme, called IPv6 (Internet Protocol, version 6) has come into play – IPv6 uses a 128-bit value to represent an address. Although there are several reasons for and advantages to IPv6,

Advance Computer Programming Domain Naming Service (DNS) – The Internet wouldn’t be a very friendly place to navigate if everyone had to refer to their addresses as numbers. – For example, it is difficult to imagine seeing “ at the bottom of an advertisement.

Advance Computer Programming The Networking Classes and Interfaces

Advance Computer Programming – several new classes were added by Java 2 – Some of these are to support the new IPv6 addressing scheme – three new classes, Inet4Address, Inet6Address, and URI, are briefly we will be discussing at the end. – java.net package’s interfaces are listed here

Advance Computer Programming InetAddress – making a phone call, sending mail, or establishing a connection across the Internet, addresses are fundamental – The InetAddress class is used to encapsulate – both the numerical IP address and the domain name for that address – Java 2, version 1.4, InetAddress can handle both IPv4 and IPv6 addresses. – We will be studying IPv4 addressing scheme.

Advance Computer Programming Factory Methods – The InetAddress class has no visible constructors. – To create an InetAddress object, you have to use one of the available factory methods – Factory methods are convention, whereby static methods in a class return an instance of that class. – Three commonly used InetAddress factory methods are

Advance Computer Programming // Demonstrate InetAddress. import java.net.*; class InetAddressTest { public static void main(String args[]) throws UnknownHostException { InetAddress Address = InetAddress.getLocalHost(); System.out.println(Address); Address = InetAddress.getByName("osborne.com"); System.out.println(Address); InetAddress SW[] = InetAddress.getAllByName(" for (int i=0; i<SW.length; i++) System.out.println(SW[i]); } Output: – default/ – osborne.com/ – –

Advance Computer Programming Instance Methods

Advance Computer Programming

TCP/IP Client Sockets – 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. – There are two kinds of TCP sockets in Java One is for servers other is for clients

Advance Computer Programming – The ServerSocket class is designed to be a “listener,” – The Socket class is designed to connect to server sockets and initiate protocol exchanges. – There are no methods or constructors that explicitly expose the details of establishing that connection