Networking in java, Advanced programming

Advanced Programming
Networking in Java
Gera
2020
1

Networking in Java
•The Java programming language is supposed to
become the premier tool for connecting
computers over the Internet and corporate
intranets and, in this realm, Java mostly lives up to
the hype.
•If you are accustomed to programming network
connections in C or C++, you will be pleasantly
surprised at how easy it is to program them in the
Java programming language.
2

Networking in Java…
•The term network programming refers to writing
programs that execute across multiple devices
(computers), in which the devices are all
connected to each other using a network.
•The java.net package of the J2SE APIs contains a
collection of classes and interfaces that provide
the low-level communication details, allowing you
to write programs that focus on solving the
problem at hand.
3

Networking in Java…
• The java.net package provides support for the two
common network protocols:
• TCP: TCP stands for Transmission Control Protocol,
which allows for reliable communication between
two applications. TCP is typically used over the
Internet Protocol, which is referred to as TCP/IP.
• UDP: UDP stands for User Datagram Protocol, a
connection-less protocol that allows for packets of
data to be transmitted between applications.
4

Implementing Servers in Java
• To implement a basic network client that receives data from the
Net, let’s implement a simple server that can send information
out to the Net.
• Once you start the server program, it waits for some client to
attach to its port.
• We chose port number 8189, which is not used by any of the
standard services.
• The ServerSocket class is used to establish a socket.
• In our case, the command establishes a server that monitors port
8189
• ServerSocket s = new ServerSocker (8189);
5

Socket Programming
•Sockets provide the communication mechanism
between two computers using TCP.
•A client program creates a socket on its end of the
communication and attempts to connect that
socket to a server.
•When the connection is made, the server creates a
socket object on its end of the communication.
• The client and server can now communicate by
writing to and reading from the socket. 6

Socket Programming…
• The java.net.Socket class represents a socket, and the
java.net.ServerSocket class provides a mechanism for the
server program to listen for clients and establish
connections with them.
• The following steps occur when establishing a TCP
connection between two computers using sockets:
• The server instantiates a ServerSocket object, denoting which
port number communication is to occur on.
• The server invokes the accept() method of the ServerSocket
class. This method waits until a client connects to the server
on the given port.
7

• After the server is waiting, a client instantiates a Socket
object, specifying the server name and port number to
connect to.
• The constructor of the Socket class attempts to connect the
client to the specified server and port number. If
communication is established, the client now has a Socket
object capable of communicating with the server.
• On the server side, the accept() method returns a reference to
a new socket on the server that is connected to the client's
socket.
8

• After the connections are established, communication
can occur using I/O streams. Each socket has both an
OutputStream and an InputStream. The client's
OutputStream is connected to the server's InputStream,
and the client's InputStream is connected to the server's
OutputStream.
• The following GreetingServer program is an example of a
server application that uses the Socket class to listen for
clients on a port number specified by a command-line
argument:
9

Manipulating URLs…
10
Compile client and Server and then start server as follows:

Manipulating URLs
• The Internet offers many protocols.
• The Hypertext Transfer Protocol (HTTP), which forms the basis of
the World Wide Web, uses URIs (Uniform Resource Identifiers)
to identify data on the Internet.
• URIs that specify the locations of documents are called URLs
(Uniform Resource Locators).
• Common URLs refer to files or directories and can reference
objects that perform complex tasks, such as database lookups
and Internet searches.
• If you know the HTTP URL of a publicly available HTML document
anywhere on the web, you can access it through HTTP.
11

•Java makes it easy to manipulate URLs.
•When you use a URL that refers to the exact
location of a resource (e.g., a web page) as an
argument to the showDocument method of
interface AppletContext, the browser in which
the applet is executing will display that resource.
12

URL Processing
•URL stands for Uniform Resource Locator and
represents a resource on the World Wide Web,
such as a Web page or FTP directory.
•The following URLDemo program demonstrates
the various parts of a URL.
•A URL is entered on the command line, and the
URLDemo program outputs each part of the given
URL. 13

14
A sample run of the program would produce the
following result:

URL Connections Class Methods:
•The openConnection() method returns a
java.net.URLConnection, an abstract class whose
subclasses represent the various types of URL
connections.
• The following URLConnectionDemo program connects to
a URL entered from the command line.
• If the URL represents an HTTP resource, the connection is
cast to HttpURLConnection, and the data in the resource
is read one line at a time. 15

16
A sample run of the program would produce the
following result:

References
➢S. Horstmann and Gary Cornell, Core Java 2 – Volume II-
Advanced Features, Sun Microsystems Press
➢Harvey M. Deitel and Paul J. Deitel, Java How to
Program, Deitel & Associates
➢Tutorials Point “Java Tutorial,” tutorialspoint.com
17
Gerabirhan Paulos
ToCourseInfo@gmail.com

Networking in java, Advanced programming

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