1. Appendix F: Network Programming in Java ©SoftMoore ConsultingSlide 1

2. Basic Network Concepts Packet (or datagram) –little bundle of information –sent from one node to another –each packet is delivered separately (possibly by different routes) Protocol –roles, vocabulary, rules for communication –network protocols (e.g., IP) versus application protocol (e.g., HTTP) IP –Internet Protocol –enables different local area networks to communicate –basis for connecting computers around the world Slide 2©SoftMoore Consulting

3. Two Types of Information Application data –the information one computer wants to send to another Network protocol data –describes how to reach the intended computer –describes how to check for errors in the transmission Slide 3©SoftMoore Consulting

4. TCP/IP: The Internet Protocol Slide 4©SoftMoore Consulting Physical Network Transport Layer (TCP, UDP) Internet Layer (IP) Application Layer (HTTP, FTP, SMTP)

5. IP Addresses IP Address –identifies a host –serves as a destination address for a packet –IPv4 (most widely deployed) 4 bytes/32 bits for an IP address Expressed using “dot” notation: 192.168.0.13 –IPv6 (the next generation) 16 bytes/128 bits for an IP address Domain name –easy-to-remember name for a host –Example: www.google.com Domain Naming Service (DNS) –translates from domain names to IP addresses Slide 5©SoftMoore Consulting

6. Socket Two-way connection Provides inter-process communication using IP Derived from BSD (UNIX) sockets Read/write streams between hosts –use either UDP and TCP protocols (layered on top of IP) –uses IP addresses and port numbers to locate servers Slide 6©SoftMoore Consulting

7. Port Meeting place on a host –one service per port Port numbers identify services on a server Range from 1 to 65535 (use type int ) Port numbers 1 through 255 are reserved for well-known services –HTTP is 80 –TELNET is 23 –etc. Port numbers less than 1024 are privileged Slide 7©SoftMoore Consulting

8. Sockets and Ports (Diagram) Slide 8©SoftMoore Consulting Client port 13 port 80 Time Service Web Service Socket Server Socket

9. Well-Known Ports 13: time 20,21: FTP 23: telnet 25: SMTP 43: whois 80: HTTP 119: NNTP 1099: RMI Slide 9©SoftMoore Consulting

10. Time of Day Service From the command prompt, enter the following command: telnet time-A.timefreq.bldrdoc.gov 13 Connects to the time-of-day service on a computer operated by the National Institute of Standards and Technology in Boulder, Colorado Gives time based on a Cesium atomic clock –result not completely accurate due to network delays Slide 10©SoftMoore Consulting By default, the telnet client is not installed on Windows Vista. To install telnet Start→ Control Panel → Programs and Features → Turn Windows features on or off → Telnet Client option

11. The Socket Class Hides the complexities of establishing a network connection and sending information across it Provides the same programming interface used for working with files Primary constructor/methods Socket(String host, int port) InputStream getInputStream() OutputStream getOutputStream() void close() Slide 11©SoftMoore Consulting

12. Streams A stream is a sequence of bytes I/O from disk, network, memory, etc. is handled in exactly the same way. Class InputStream abstract int read() abstract void close() Class OutputStream abstract void write(int b) abstract void close() Slide 12©SoftMoore Consulting

13. Class PrintStream Method print() outputs an object, primitive, or string. Method println() does the same thing, but it adds a newline at the end. Object System.out is a PrintStream. Example PrintStream ps = new PrintStream(outputstream); Slide 13©SoftMoore Consulting

14. Class BufferedReader Provides method String readLine() Examples InputStreamReader isReader = new InputStreamReader(System.in); BufferedReader reader = new BufferedReader(isReader) Slide 14©SoftMoore Consulting

15. Example: Using Sockets import java.io.*; import java.net.*;... Socket s = new Socket("time-A.timefreq.bldrdoc.gov", 13); InputStream is = s.getInputStream(); InputStreamReader isReader = new InputStreamReader(is); BufferedReader in = new BufferedReader(isReader); String line; while ((line = in.readLine()) != null) System.out.println(line); in.close();... Slide 15©SoftMoore Consulting

16. Example: Simple Browser Using Sockets import java.net.*; import java.io.*; public class SimpleHttpBrowser { public static void main(String[] args) throws Exception { String host = args[0]; int port = Integer.parseInt(args[1]); Socket s = new Socket(host, port); InputStream inStream = s.getInputStream(); OutputStream outStream = s.getOutputStream(); Slide 16©SoftMoore Consulting

17. Example: Simple Browser Using Sockets (continued) PrintWriter out = new PrintWriter( new OutputStreamWriter(outStream), true); BufferedReader in = new BufferedReader( new InputStreamReader(inStream)); out.println("GET / HTTP/1.1"); out.println("Host: " + host + ":" + port); out.println(); String line; while ((line = in.readLine()) != null) System.out.println(line); in.close(); out.close(); } Slide 17©SoftMoore Consulting

18. Client/Server Overview Can communicate with remote file systems using a client/server model Server listens for connection requests from clients Clients know how to connect to the server via a port number Upon connection, server processes the request coming across the network from the client Connection can remain open or shut down after each transaction Slide 18©SoftMoore Consulting

19. Client-Server Client – initiates connection –retrieves data –displays data –responds to user input –requests more data Examples –web browser –chat program –PC accessing files Server – responds to connection –receives data request –looks up data –delivers it Examples –web server –database server –email server –domain name server Slide 19©SoftMoore Consulting Difference between client and server is relative – it’s just peers talking to each other.

20. URL Format –protocol://host[:port][/path/][file][#anchor] Examples –http://www.softmoore.com –http://www.softmoore.com/Bib-5.2-JavaAdvanced.html –http://java.sun.com/sfaq/index.html –http://java.sun.com/sfaq/ –ftp://ftp.cs.rpi.edu/pub/stl/ –http://64.233.187.99:80/ (same as http://www.google.com) Slide 20©SoftMoore Consulting

21. java.net.URL URL(String) –creates a URL object from the String representation URL(String, String, int, String) –creates a URL object from the specified protocol, host, port number, and file URL(URL context, String spec) –creates a URL by parsing the specification spec within a specified context. InputStream openStream() –opens a connection to this URL and returns an InputStream for reading from that connection Slide 21©SoftMoore Consulting

22. java.net.URL (continued) URLConnection openConnection() –Returns a URLConnection object that represents a connection to the remote object referred to by the URL. MalformedURLException –thrown if you try to create a bogus URL –usually means bad user input, so fail gracefully and informatively accessor methods –getProtocol()– getHost() –getPort()– getFile() –getRef() Slide 22©SoftMoore Consulting

23. java.net.URLConnection InputStream getInputStream() –returns an input stream that reads from this open connection –makes the connection if it has not already been made URLConnection creates the socket and handles the protocol (e.g. HTTP) for you There are also handlers for other protocols –ftp, gopher, file, mailto, or you can write your own –getOutputStream() Handles relative URLs via CodeBase/DocumentBase Slide 23©SoftMoore Consulting

24. java.net.URLConnection (continued) Object getContent() Makes the connection if it hasn’t already been made Returns an object that’s appropriate for this file’s MIME type For text, returns an InputStream For images, returns an ImageObserver Only supports text/plain, text/Generic, image/gif, and image/jpeg You can add your own ContentHandler if you like Slide 24©SoftMoore Consulting

25. Example: Simple Browser Using URLs import java.net.*; import java.io.*; public class SimpleBrowser { public static void main(String[] args) throws Exception { URL url = new URL(args[0]); InputStream is = url.openStream(); InputStreamReader isReader = new InputStreamReader(is); BufferedReader in = new BufferedReader(isReader); String line; while ((line = in.readLine()) != null) System.out.println(line); in.close(); } Slide 25©SoftMoore Consulting

26. java.net.HttpURLConnection Extends URLConnection with additional support for HTTP connections. Usage: Cast a URLConnection URL url = new URL("http://www.android.com/"); HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); Selected methods in HttpURLConnection –int getResponseCode() –String getResponseMessage() –String getHeaderField(int n) –String getHeaderFieldKey(int n) Slide 26©SoftMoore Consulting

27. Slide 27 Networking Application: Checking URLs URLConnection conn = url.openConnection(); if (conn instanceof HttpURLConnection) { HttpURLConnection httpConn = (HttpURLConnection) conn; // response code 400 or higher is bad if (httpConn.getResponseCode() >= 400) printBadUrl(url, httpConn.getResponseCode(), httpConn.getResponseMessage()); } else printFeedback("Skipping " + url + ": not HTTP protocol");

28. java.net.URLEncoder static String encode(String) The ASCII characters ‘a’ through ‘z’, ‘A’ through ‘Z’, and ‘0’ through ‘9’ remain the same. The space character is converted into a plus sign ‘+’. All other characters are converted into the 3-character string “%xy”, where xy is the two-digit hexadecimal representation of the lower 8-bits of the character. Slide 28©SoftMoore Consulting