1. 1 Network Programming Introduction zBased on Classes in the java.net package zLecture focuses on: yTCP and UDP yNetwork programming basics yIdentifying a machine yServers and Clients yPorts and sockets yData transfer using sockets

2. zLots of java programs use Transmission Control Protocol (TCP) zConnection-based (where java stream sockets provides continuous data stream), reliable, data streams will always get there. Also high overhead. We will focus on TCP/IP sockets. zUser Datagram Protocol (UDP) is not connection-based (connectionless service with datagram sockets allowing one message, an unreliable protocol which is much faster, but the message won’t always get there TCP and UDP

3. Network Programming Basics The classes in java.net : Java programs can use TCP or UDP to communicate over the Internet. The URL, URLConnection (for Web applications), Socket, and ServerSocket (client-server applications) classes all use TCP to communicate over the network. The DatagramPacket, DatagramSocket, and MulticastSocket classes are for use with UDP.

4. Network Programming Basics zHistorically error-prone, difficult, complex zJAVA has complete network package, java.net zI/O stream library works quite well for TCP/IP zThreading is also very useful and relatively easy here

5. Identifying a Machine zUniquely identify a machine from all the others in the world zIP (Internet Protocol) address that can exist in two forms:

6. Identify a Machine (Continue) ÀDNS(Domain Name Service) form xjava.sun.com Á“Dotted quad” form: x123.255.28.120 y static InetAddress.getByName() produces java object containing address

7. Servers and Clients zTwo machines must connect zServer waits for connection zClient initiates connection (create socket) zOnce the connection is made, server & client look identical

8. Testing w/o a network zFor testing your program, you can do it w/o network. (server & client on same machine) zLocalhost: the IP address for testing without a network zThree ways to identify:

9. Test w/o networking (Continue) zInetAddress y addr=InetAddress.getByName(null); zEquivalently: yInetAddress.getByName(“localhost”); zOr using the reserved IP number for the loopback: yInetAddress.getByName(“127.0.0.1”);

10. Port number zIP address isn’t enough to identify a unique server zmany servers can exist on one machine zport number: Unique in a Machine zNot a physical location, but a software abstraction to represent a service

11. Port number (Continue) zWhen set up client and server, you must specify IP address and port. zPort number range: 0 to 65,535 z1-1024 are reserved, others may be used.

12. Sockets z Software abstraction used to represent the connection between two machines z Socket is the actual 2-way connector.

13. Sockets z The following sequence establishes a socket from the client class InetAddress addr = InetAddress.getByName(null); Socket socket = new Socket(addr, 8080);

14. Sockets z At the server class, the following establishes the server port, and waits for a client request to establish a socket ServerSocket s = new ServerSocket(8080); Socket socket = s.accept();

15. Data transfer using sockets zOnce you have a Socket, you call getInputStream() and getOutputStream() to produce the corresponding InputStream and OutputStream objects zYou can convert these to readers and writers, wrap them in a BufferedReader or BufferedWriter and PrintWriter

16. Data transfer using sockets (continue) z At the server and client classes BufferedReader in = new BufferedReader( new InputStreamReader( socket.getInputStream())); PrintWriter out = new PrintWriter( new BufferedWriter( new OutputStreamWriter( socket.getOutputStream())),true);

17. Data transfer using sockets (continue) zFrom then on, it’s like reading and writing any other I/O stream! while (true) { String str = in.readLine(); if (str.equals("END")) break; System.out.println("Echoing: " + str); out.println(str); } Example: JabberClient JabberServerJabberClientJabberServer