1. Networking with Java CSc 335 Object-Oriented Programming and Design Spring 2009

2. Networking with JavaN-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.

3. Networking RefactoringY-3RefactoringY-3RefactoringY-3 ConcurrencyNetworksSerialization Javadoc JUnit Eclipse Debugging Testing & Maintaing Large Programs Teams Reading others’ code Reading others’ code MVC Observer Observable Design Patterns Design Patterns UML Class Diagrams Inheritance Hierarchy Inheritance Hierarchy Coupling/ Cohesion OO Design PITL Sequence Diagrams Package Diagrams Anonymous Classes Abstract Classes Packages JDK/JRE Java Language Compile-Time Run-Time Type Resolution Type Checking Java Swing Frameworks Java API Inversion of Control Layout Manager Listeners Events I/O Iterator Collection Exceptions Composite Command Template Decorator N-3

4. Networking with JavaN-4 Outline Introduction to Networking Concepts Client-Server and Peer-to-Peer Sockets Streams Networking in Java Summary

5. Networking with JavaN-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 u Many clients connect with one server. u Clients communicate only with server. Peer-to-Peer u Clients connect to a group of other clients, with no server. u Clients communicating directly with each-other.

6. Networking with JavaN-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

7. Networking with JavaN-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 code

8. Networking with JavaN-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.

9. Networking with JavaN-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.

10. Networking with JavaN-10 Outline Introduction to Networking Concepts Networking in Java Sockets Streams Decorating Streams Summary

11. Networking with JavaN-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

12. Sockets in Java Networking with JavaN-12 Host Machine Process Host Machine Process Server Socket Input Socket Output Socket Input Socket Process Socket Host Machine

13. Networking with JavaN-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.

14. Networking with JavaN-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

15. Networking with JavaN-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.