Java Network Programming

Transcription

1 CPSC 360 Network Programming Java Network Programming Michele Weigle Department of Computer Science Clemson University January 24, The Application Layer The client-server paradigm Typical network has two pieces: client and server :» Initiates contact with server ( speaks first )» Requests service from server» For Web, client is implemented in browser; for , in mail er :» Provides requested service to client» Always running» May also include a client interface transport network link physical local ISP company network reply request regional ISP transport network link physical 2

2 / Paradigm Socket programming Sockets are the fundamental building block for client/server systems Sockets are created and managed by s» Strong analogies with files a host-local, created/released, OS-controlled interface into which an can both send and receive messages to/from another (remote or local) Two types of transport services are available via the API:» UDP s: unreliable, datagram-oriented communications» TCP s: reliable, stream-oriented communications 3 / Paradigm Socket-programming using TCP A is an created, OS-controlled interface into which an can both send and receive messages to and from another» A door between es and end-to-end transport protocols developer operating system developer operating system 4

3 Socket-programming using TCP TCP programming model A TCP provides a reliable bi-directional communications channel from one to another» A pair of pipes abstraction 5 Socket-programming using TCP Network addressing for s Sockets are addressed using an IP address and port number End System Local port numbers (e.g., 6500) addresses of hosts (e.g., ) End System domain name of host e.g., access.cs.clemson.edu DNS 6

4 Socket-programming using TCP Socket programming in Java creates a local TCP specifying the host and port number of server» Java resolves host names to IP addresses using DNS contacts server» must be running» must have created that welcomes client s contact When the client creates a, the client s TCP establishes connection to server s TCP When contacted by a client, server creates a new for server to communicate with client» This allows the server to talk with multiple clients 7 Socket-programming using TCP Socket creation in the client-server model 3-way handshake client host or server TCP 3-way handshake welcoming connection 8

5 Socket-programming using TCP Simple client-server example stdin stdout client welcoming connection The client s a line of text from standard input and sends the text to the server via a The server receives the line of text from the client and converts the line of characters to all uppercase The server sends the converted line back to the client The client receives the converted text and s it to standard output 9 Socket programming with TCP Example structure s from standard input (infromuser stream), s to server via a (outto stream) s line from a converts line to uppercase and s back to client s from, (infrom stream) prints modified line to standard output outto infrom client (2) (3) Standard output (4) Standard input infromuser (1) 10

6 Socket programming with TCP Example /server TCP interaction in Java (running on torpedo1.cs.clemson.edu) create for incoming request (port=6789) welcomesocket = new Socket(...) wait for incoming TCP connection request connection setup connectionsocket = welcomesocket.accept() request from connectionsocket (running on shadow1.cs...) create, connect to torpedo1.cs.clemson.edu, port=6789 = new Socket(...) request using reply to connectionsocket reply from program flow close connectionsocket close data flow 11 Socket-programming using UDP UDP programming model A UDP provides an unreliable bi-directional communication channel from one to another» A datagram abstraction 12

7 Socket programming with UDP Example /server UDP interaction in Java (running on torpedo1.cs.clemson.edu) create for incoming request (port=9876) serversocket = new DatagramSocket() request from serversocket create, = new DatagramSocket() create address (torpedo1.cs.clemson.edu, port = 9876) and send datagram using reply to serversocket specifying client IP address and port number reply from close program flow data flow 13