Cup 10: Networking

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Cup 10 Networking

• Special Topics Java

Dr. Tim Margush Department of Mathematics and
Computer Science The University of Akron
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java.net

• Contains classes related to networking
• IP Address
• Uniform Resource Locator (URL)
• Sockets
• Server and regular sockets
• Transmission Protocols
• TCP/IP
• UDP

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IP Addresses

• 130.101.5.4
• dotted quad format
• kira.cc.uakron.edu
• domain name format
• The following ststic methods return a new
  InetAddress object
• InetAddress.getByName(String)
• InetAddress.getLocalHost()

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InetAddress Class

• getAllByName(String)
• returns an array of InetAddress objects
• UnknownHostException
• getHostAddress()
• returns the IP address as a String in dotted quad
  format
• getHostName()
• returns the domain name

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Uniform Resource Locator

• Protocol
• HTTP, FTP, GOPHER, FILE, NEWS
• Host
• dotted quad or domain name format
• Port
• 0-1024 are more or less reserved
• File
• A String representing the resource

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URL Class

• URL(String, String, int, String)
• URL(String, String, String)
• port number is implied by the protocol
• URL(String)
• "http//www.cs.uakron.edu/index.html"
• URL(URL, String)
• creates a relative URL, parsing the String within
  the context of the given URL

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Establishing a Connection with a URL

• URLConnection openConnection()
• Instantiates a connection Object for the the URL
• connection settings are manipulated before the
  actual connection is established
• Method connect() establishes the connection using
  the appropriate protocol handler and settings of
  the URLConnection object

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Using a Connection with a URL

• Object getContent()
• InputStream getInputStream()
• A URL's openStream() method is a shortcut for the
  two-step process URL.openConnection().getInputStr
  eam()
• OutputStream getOutputStream()
• String getVariousHeaderInfo()

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Sockets

• Stream - supports active communications between
  two computers
• a route is established
• data is streamed in packets
• receipt is verified before the next packet is sent

• Datagram - supports connectionless communication
  (UDP)
• message is broken into packets and sent to a
  router
• packets bounce between routers until they arrive
  at their destination
• packets must be reassembled to retrieve the
  message

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Client Sockets

• Socket cs new Socket(addr, port)
• applt-gtclientlt------gtserverlt-gtapp
• InputSream and OutputStream objects are
  constructed from the socket to support transfer
  of data
• The remote socket is usually created by a server
  to form the other end of the connection

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Boilerplate Server

• ServerSocket server new ServerSocket(1234)
• Socket sock server.accept()
• Thread is blocked at this statement until a
  connection request occurs which causes a new
  Socket to be created to form the other end of the
  communications stream
• InputStream in sock.getInputStream()
• OutputStream out sock.getOutputStream()

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Datagram Client/Server

• The server and client simply create a Datagram
  socket
• Datagram socket new DatagramSocket(port)
• The system will assign a port number if you do
  not request one
• The server should specify a port number so the
  client knows where to send the datagrams

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DatagramPacket

• new DatagramPacket(msg, len, addr, port)
• This creates a packet to be sent
• msg is a byte array
• len is the size of the msg (in bytes)
• addr is the InetAddress the package is going to
• port is the port number on the receiving end

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Sending and Receiving Datagrams

• socket.send(aPacket)
• Packet is sent out on the Internet and is routed
  toward the destination
• socket.receive(anotherPacket)
• This is a blocking statement that waits for a
  datagram to be received.
• anotherPacket was created with no address info,
  just a byte array and length

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Decoding a Received DatagramPacket

• pack.getAddress()
• pack.getPort()
• pack.getLength()
• pack.getData()
• set methods