Networking

1
Networking

• Robert Salkin
• CSI 445 Advanced Java
• Summer 2006, 6W3

2
What is Networking?

• Networking is the ability for threads of
  execution to communicate with other threads of
  execution on the same computer or another
  computer using Internet facilities.
• java.net contains many useful classes for this
  task.

3
Network Participants

• Client
• Attempts to connect.
• Requests information.
• Server
• Accepts a connection.
• Responds to requests.
• Together, they make a client-server relationship.

4
Communication Types

• Stream or Socket-based
• A connection is established between client and
  server.
• Data is guaranteed to arrive.
• The connection type most often used.
• Datagram or Packet-based
• Connectionless.
• Packets may be lost, disordered, or duplicated.
• Not often used, except for streaming data where
  packet loss is preferred over the slow down due
  to the connections overhead.

5
World Wide Web

• The protocol used on the World Wide Web (WWW) is
  HTTP (Hypertext Transfer Protocol).
• Resources may be accessed on the WWW via HTTP
  using a URL (Uniform Resource Locator).
• A URL is a URI (Uniform Resource Identifier) for
  documents.

6
WWW Components

• A URL object can be used to represent a document
  location.
• URL url new URL( http//java.sun.com/ )
• The contents of the page represented by the URL
  can be retrieved and displayed in different ways
• In a JApplet
• getAppletContext().showDocument(url)
• In a JEditorPane
• ep.setPage(url)
• Storing the data
• Object o url.getContent()
• Assuming it is HTML, cast it to a string.

7
Addresses and Ports

• An IP (Internet Protocol) address is a unique
  series of numbers used to identify a specific
  computer on the internet.
• A (software) port is an address internal to a
  computer, used to route incoming data to the
  correct application.

8
Stream Sockets (Server)

• Create a ServerSocket
• ServerSocket server new ServerSocket(port)
• Wait for a connection (and accept it)
• Socket sock server.accept()

9
Stream Sockets (Client)

• Open a Socket connection with the server address
  and port
• Socket conn new Socket( addr, port)
• Or, create the socket, then open the connection
• conn.connect(address)

10
Address Conversion

• The InetAddress class has useful methods to
  specify addresses
• getByName(localhost)
• getLocalHost()

11
Data Transfer

• To send and receive data, use the input and
  output streams
• conn.getInputStream()
• conn.getOutputStream()
• Wrap those streams with
• ObjectInputStream
• ObjectOutputStream
• or
• Scanner
• Formatter

12
Remember to Close

• As with a file (and streams!), close sockets when
  they are no longer needed
• conn.close()