CS51 - Spring 2010 - Lecture 25

  • administrative
       - if you're a senior and I haven't talked to you, let me know ASAP
       - last CS lunch of the semester on Thursday at noon in Frank West

  • sending/receiving data externally
       - What type of data am I sending?
          - characters/strings
             - use Readers and Writers
          - built-in types
             - use DataInputStream/DataOutputStream
          - objects and or a mixtures of types
             - use ObjectInputStream/ObjectOutputStream
       - Buffered or unbuffered?
          - Unbuffered data sends immediately
          - Buffered data queues it up and then sends it in larger chunks
          - Often we'll want to buffer our data, but sometimes immediate action is necessary
          - For reader/writers
             - BufferedReader
             - PrintWriter
          - For streams
             - BufferedInputStream
             - BufferedOutputStream

  • show SimpleIM demo
       - only need client/server relationship to know who should contact who
       - how does this work for most IM clients?

  • what needs in happen in IM program?
       - establish a connection (should look similar to DrawingPanelNetwork)
          - from these we get a socket (multidirectional)
       - both the client and the server now should do the same thing
          - get reader/writers for both input and output
          - if we have text to write, send it out
          - if we receive text, display it
       - what type of I/O classes should we use (Streams or Reader/Writer)?

  • show SimpleIM code
       - SimpleIM.actionPerformed
          - what are the actions?
          - notice that we use the same class for both the server and the client
          - when the user enters text, we set the text for the message handler
       - IMMessageHandler
          - again, random port
             - http://en.wikipedia.org/wiki/TCP_and_UDP_port
             - http://www.iana.org/assignments/port-numbers
          - after establishing a connection, they do the same thing
          - use BufferedReader and PrintWriter because we're dealing with Strings/characters
             - also give us the ability to send a line at a time
             - use InputStreamReader to go from a stream to a reader
          - ready() returns true if there is data to read, false otherwise
          - see if we have text to send, if so, send it
          - just keep looping

  • Look at the mystery method in Mystery class
       - what does it do?

  • show HTMLLinkFinderBufferedReader demo

  • show HTMLLinkFinderBufferedReader code
       - getWebPage method
          - creates a new URL object
             - URL = uniform resource locator
          - url.openStream()
          - read the data using a BufferedReader
          - new String(buildpage), could also have used builldpage.toString()
          - throws MalformedURLException

  • show HTMLLinkFinderUsingSockets code
       - does the same thing, but we've implemented the interaction in the HTTPConnection class
       - notice it call getHost() on the url, then calls getPage
       - what is the difference between a host and a page?
       - why does this version of the URL constructor have two parameters?

  • show HTTPConnection class in HTMLLinkFinderUsingSockets code
       - constructor
          - uses sockets
          - we're the client
          - open a socket to the host at port 80
             - port 80 is the standard port for http, which is for web data
          - need to open both input and output streams, why?
          - true specifies autoflush, i.e. println() flushes the buffer
       - getWebPage
          - we have a connection to the server, but need to tell it what we want
          - "GET pagename" tells the server we want the html for pagename
          - web servers automatically disconnect after sending data. Why do you think this is?
       - readResponse

  • telnet
       - telnet is a command line program with similar functionality to HTTPConnection
       - "telnet <host_name> <port>" will open a connection
       - standard web server port is 80
          - "telnet www.google.edu 80"
       - to fetch a web page once you have a connection open:
          GET <page_name> HTTP/1.1
       - a common page is "/index.html"
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