Lab#3 Sockets (i) Book reading: Kurose 2.7

Other info: •

http://download.oracle.com/javase/6/docs/api/index.html

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The Sockets API ◦ What is a Socket? What identifies a socket? ◦ Types of sockets

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Sockets in Java ◦ TCP Sockets ▪ Socket class. Use of close. ▪ TCP Clients •

Exception handling with try … catch

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Readin from a socket: getInputStream. Line oriented reading with Scanner class. Methods: next, nextInt, nextLine, hasNext …. ◦ Reading from the keyboard.

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Writing to a socket: getOuputStream. Text-oriented write : PrintWriter class. ◦ print & println. Warning: platform-depented end-of-line. ▪ Warning: The need of flushing buffers to avoid a deadlock. método flush (flush method on clases OutputStream & PrintWriter).

◦ InetAddress class for Internet Addresses in Java. ▪ How to learn about addresses in use in the current connection: métodos getLocalPort, getPort, getLocalAddress and getInetAddress. ▪ Getting parameters from standard input. Convert an String into an int for port numbers.

Exercises: •

Exercise#1: Write a program that will connect to port 80 at server “www.upv.es”, printing the message “Connected!” after establishing the connection and next closing the connection and ending. (No need to include exception handling code).

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Exercise#2: Add another method to the program above. This new method will do as #1 but now exception handling is required (using try … catch). Change the connected message to string “Connected again!”. •

Run it and check it works too.

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Now change port number to 81 and try again. What happens?

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Restore port number to 80. Change the server name adding an additional “w” to the name. Try again to see what happens.

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When trying to connect a socket, when do UnknownHostException and IOException happen?

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Exercise#3: Add a new method to your program that will connect to port 25 on “smtp.upv.es” server, after the connection is made, it will read the first text line from the socket and it will print it to the standard output.

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Exercise#4: Daytime client. It just connects to port 13 on “ntp.upv.es” server and it prints a single line to stdout.

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Exercise#5: Basic HTTP/1.0 client. It will connect to port 80 on “www.upv.es” server and it will transmit the text “GET / HTTP/1.0\r\n\r\n”. Next it will wait for any received text over the socket that will be printed to stdout.

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Excercise#6: Add yet another method to your program. This time it will be a client connecting to port 25 on UPV STMP server (smtp.upv.es). Once the connection is established, the program will show the values of local and remote port and the IP address of the server. Run it three times and notice the changes in the values shown.

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Exercise#7(optional): Make changes to the program above so it will accept server name and port number as command line arguments.