Networking with Java

CSc 335Object-Oriented Programming and Design

Spring 2009

Networking with Java N-2

Acknowledgements

• These slides were written by Craig Barber.

• Some slides from Martin Stepp were used.

• The slides were modified slightly by Richard Snodgrass and reorganized by Ivan Vazquez.

Networking

Refactoring Y-3Refactoring Y-3Refactoring Y-3

ConcurrencyNetworksSerialization

Javadoc

JUnitEclipse

Debugging

Testing &Maintaing

LargePrograms

Teams

Reading others’code

MVC

ObserverObservable

DesignPatterns

UML

ClassDiagrams

InheritanceHierarchy

Coupling/Cohesion

OO Design

PITL

SequenceDiagrams

PackageDiagrams

AnonymousClasses

AbstractClasses

Packages

JDK/JRE

Java Language

Compile-TimeRun-Time

Type ResolutionType Checking

Java Swing

Frameworks

Java API

Inversionof Control

Layout Manager

ListenersEvents

I/O

Iterator

Collection

Exceptions

Composite

CommandTemplate

Decorator

N-3

Networking with Java N-4

Outline

• Introduction to Networking Concepts Client-Server and Peer-to-Peer Sockets Streams

• Networking in Java

• Summary

Networking with Java N-5

What is “Networking”• What is “Networking”?

Basic: getting two or more computers to send data to each other

Practical: having programs on separate computers interact with one another

• Types of Networking Client - Server

Many clients connect with one server. Clients communicate only with server.

Peer-to-Peer Clients connect to a group of other clients, with no server. Clients communicating directly with each-other.

Networking with Java N-6

Client - Server Networking• Advantages:

Easier to implement Less coordination

involved Easier to maintain

control of users

• Disadvantage: Relies on one main

server for entire operation

Networking with Java N-7

Peer-to-Peer Networking• Advantages:

No main server Easier for clients to enter and

leave Easier for spreading updates

• Disadvantages: Less control over users Harder to coordinate More difficult to implement

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Networking with Java N-8

How Does Networking Work?

• Computers connect to each other through links called sockets, each associated with a single computer.

• A network stream is created by connecting a socket on one computer to a socket on another computer.

• Applications communicate by sending data through streams to each other.

• Note: streams are also used in Java for input and output.

Networking with Java N-9

Sockets• A socket is a connection on one computer used to send

data back and forth

• The application consists of multiple processes, one running on each computer.

• Sockets are created by the process on each computer.

• The sockets then establish a connection to each other. One process sets up a server socket to receive a connection. The other process sets up a client socket to establish the

connection with the server socket.

Networking with Java N-10

Outline

• Introduction to Networking Concepts

• Networking in Java Sockets Streams Decorating Streams

• Summary

Networking with Java N-11

Sockets in Java

• Found in java.net package

• java.net.ServerSocket Accepts new incoming connections Creates new ServerSocket for each connection

• java.net.Socket Connects to an existing ServerSocket, through the network

Networking with Java

Sockets in Java

N-12

Host Machine

Process

Host Machine

Process

ServerSocket

InputSocket

OutputSocket

Socket

Socket

Socket

InputSocket

Process

Socket

Host Machine

Networking with Java N-13

java.net.ServerSocket• public ServerSocket( int port )

Throws IOException Creates a ServerSocket to accept new connections at the specified

port

• public Socket accept( ) Throws IOException Waits for an incoming connection, establishes the new connection, and

returns a socket for that connection Multiple applications can connect to the same ServerSocket

• public void close( ) Throws IOException Closes the server socket. Does not close open sockets.

Networking with Java N-14

java.net.Socket• public Socket( String host, int port )

Throws IOException, UnknownHostException Connects to a server socket at the provided address (host) on the provided

port

• public InputStream getInputStream( ) Throws IOException Returns the input stream from the socket

• public OutputStream getOutputStream( ) Throws IOException Returns the output stream from the socket

• public void close( ) Throws IOException Closes the connection

Networking with Java N-15

Summary

• Networking is actually doable, when using Java’s convenient API.

• Networking is integrated with input and output: both use streams.

• Decorators make your life much easier.

• Advanced applications often use serialization and threads.