Misc. Java

1
Misc. Java

• Alittle more network programming
• Using jar files to share your work

2
Socket Java Network Connection

• Analogous to an electrical socket, the client can
  plug into the server
• This creates a connection along which information
  can flow
• When the client disconnects, the socket is free
  for the next client to use
• Input and output streams can be created to allow
  communication over the socket.
• But I want to experiment at home

3
You know an IP number
4
Date Server Example (unchanged)

• import java.util.Dateimport java.net.import
  java.io.public class DateServer static
  final public int portNumber 4291 public
  static void main(String args) try
  DateServer world new DateServer()
  catch (IOException e) System.out.println("IO
  exception " e) // end try-catch //
  end main public DateServer ( ) throws
  IOException ServerSocket server new
  ServerSocket(portNumber) for (int i 0 i lt
  3 i) System.out.println("Waiting for a
  client") Socket sock server.accept() Sys
  tem.out.println("Got client "
  i) OutputStreamWriter out new
  OutputStreamWriter(sock.getOutputStream())
  String message "Current date and time is "
  new Date() "\n" out.write(message) out
  .close() // end for // end DateServer
  // end class DateServer

5
Date Client Example

• import java.net.import java.io.public
  class DateClient static final public int
  portNumber 4291 public static void
  main(String args) try DateClient
  world new DateClient() catch (IOException
  e) System.out.println("Received an IO
  exception " e) // end try-catch //
  end main public DateClient ( ) throws
  IOException // Socket sock new
  Socket(InetAddress.getLocalHost(), portNumber)
  byte ipAddr (byte) 134, (byte) 161,
  (byte) 243, (byte) 240 Socket sock new
  Socket(InetAddress.getByAddress(ipAddr),
  portNumber)// Socket sock new
  Socket(InetAddress.getByName("fienup2.cs.uni.edu")
  ,
• portNumber) Reader
  isread new InputStreamReader(sock.getInputStream
  ()) BufferedReader input new
  BufferedReader(isread) System.out.println("
  message is " input.readLine()) // end
  DateClient // end class DateClient

6
Possible Limitations/Problems

• Your internet service provider might only give
  you one IP address. That you share between
  machines.
• The IP address might vary, i.e., assigned
  dynamically each time you connect.

7
Making a Double-Clickable .jar File

• Some of you have written Frogger games of which
  you are quite proud. You want to share your
  handiwork with your friends, family, potential
  employers.
• How you can you make a double-clickable
  application from your Java program?
• Many industry-grade development environments
  include tools for creating double-clickable apps.
  But we are not using one.
• Many of these professional tools are quite
  complex. Learning them just for the sake of
  creating a double-clickable app seems crazy.
• Without making a double-clickable app, your
  program will be hard or impossible for many
  others to use.
• Therefore, use the Java Development Kit's jar
  tool to create a double-clickable Java archive
  file.
• jar packages a bunch of files into a single
  archive file that you can give to another or
  offer for download on the web.
• If we tell the archive which class file contains
  the main() method, then users will be able to
  double-click on the file's icon and run it like a
  standalone application.
• The file that tells the archive this information
  is called a manifest file.
• The manifest acts like a "read me" file for the
  Java virtual machine can read. When we run jar,
  it automatically creates a manifest file for the
  archive. Unfortunately, the default manifest file
  does not include a definition of the class that
  contains the main() method.

8
Making a Double-Clickable .jar File

• Here are the steps you can use to create a
  double-clickable jar file. I'll illustrate them
  by creating the double-clickable cannonworld.jar.
  
• Create a manifest file, manifest.mf for your
  application and place it in the directory with
  .class files
• Manifest-Version 1.0
• Created-By 1.5.0_06
• Main-Class CannonGameDriver
• Go to your Unix shell (or perhaps Windows DOS
  window). Change into the directory containing
  your .class files and manifest.mf.
• Use jar to create your archive. The command you
  need is
• jar cfm jarFileName manifest.mf .class
• where jarFileName is what you want to call your
  archive.
• To create my archive, I entered
• jar cfm cannonworld.jar manifest.mf .class
• Move your jar file to whatever location you
  desire.
• It's also fun to make your own icon for the
  double-clickable file. That's another one of
  those things that industrial-strength IDEs offer
  do for us. jar does not.
• You can read more about jar by typing "man jar"
  at your Unix prompt, or by visiting the JDK
  documentation.