Objectives:1. Archiving and Packaging Java Code

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JAR Files

• Objectives 1. Archiving and Packaging Java Code
• 2. The jar Program
• 3. Example Applet

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JAR Files

• JAR file archives provide packaging for
  applications, applets, JavaBeans
• Multiple classes can be packaged in JAR files
• JAR Files specified within HTML
• Manifest file
• JAR files use ZIP compression format

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JAR Files

• provide a delivery mechanism for JavaBeans,
  packaging all the necessary resources together in
  a single file. Multiple Beans may be contained
  in a single JAR file, and the file may also
  contain an optional manifest which lists the
  contents.
• help transport Beans over the Internet in
  easy-to-manage packages, and they are also used
  to archive applets for more efficient downloading
  performance.

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The jar Utility

• Creates JAR files
• Adds to existing archives
• Extracts items in an archive
• Lists archive contents
• Syntax
• jar ctux vfm0M jar-file manifest-file
  files

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jar Command jar ctux vfm0M jar-file
manifest-file files

• jar-file specifies the name of the archive
  file. No required naming conventions exist for
  Java archive files, although you will most likely
  see the file extension .jar associated with them.
  
• The manifest-file argument is a file containing a
  list of the jar file contents. A manifest file is
  required when using the m command line option.
• More...

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jar Command jar ctux vfm0M jar-file
manifest-file files

• files to be archived are listed at the end of the
  command and are separated by whitespace.
• Wildcard characters are accepted
• directory names are followed recursively, i.e.,
  all files in subdirectories will also be
  archived.
• File names are relative to the directory from
  which you run the jar command
• special C option introduced in Java 1.2 to
  change the relative directory.
• forward or backward slashes are accepted, making
  the jar command operating-system independent.

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jar command line options

• Only one of the following
• c Create a new archive file
• t List the table of contents for the archive
  file
• u Update the contents of the archive or manifest
• x Extract named files (or all) from the archive
• Other options can be combined or omitted
• v Verbose output
• f Specify jar-file
• m Include information from manifest-file
• 0 Do not use compression
• M Do not create a manifest file for the archive
  entries

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Examples of jar command

• Create an archive called Simulator.jar that
  contained the single class Machine.class
• jar cf Simulator.jar Machine.class
• List the table of contents of Simulator.jar
  using verbose output
• jar tvf Simulator.jar
• Extract all contents of Simulator.jar
• jar xvf Simulator.jar

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JAR Files HTML

• Improve Applet download performance
• compression of JAR files allows efficient
  downloading of applets over the Web.
• entire archive may be downloaded in a single HTTP
  transaction.
• avoids reconnect each time a specific .class file
  or resource is needed.
• ARCHIVE Tag
• ltAPPLET ARCHIVESimulator.jar CODEStock.class
  WIDTH350 HEIGHT250gt
• lt/APPLETgt
• filename is relative to the location of the HTML
  page.
• still need a CODE tag to indicate which class
  within the archive starts the applet.

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The Manifest

• The manifest file exists to provide information
  about the contents of its associated jar file.
• Automatically created
• if not specified otherwise, named manifest.mf
• placed in the archive under a directory called
  /META-INF
• M option in jar command suppresses creation.
• Lists the entries in the archive
• First entry identifies manifest version Example
• Manifest-Version 1.0
• Created-By 1.5.0 (Sun Microsystems Inc.)
• applies to the entire JAR file

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Manifest Contents

• Subsequent sections must begin with
• Name ltentrygt
• describe individual elements JavaBeans, files,
  packages, and URLs.
• Each section of the manifest file refers to an
  entry in the archive and is separated by a blank
  line.
• Attribute-value pairs of the format attribute
  value are used in each section to give
  information about that particular entry.
• Name Calculator.class
• lines describing this file
• Name edu/weber/mypkg
• lines describing this package

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Manifest Contents

• Attribute/Value pairs
• Note Java-Bean attribute in example
• Name StockBroker/Simulator/Stock.class
• Digest-Algorithms MD5 SHA
• MD5-Digest wuXrtYN-56Nn4rtDFewq-tr
• SHA-Digest fg67tKdkfR65-SRkdrslegvY-tyK
• Java-Bean True

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Custom Manifest File Indicating Beans

• Manifest-Version 1.0
• Name StockBroker/Simulator/Stock.class
• Java-Bean True
• Name StockBroker/Simulator/Helper.class
• Java-Bean False
• Name StockBroker/Simulator/Price.class
• Java-Bean True

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Creating the Archive File

• create an archive file with a customized
  manifest file by using both the m and f options
  and giving the required arguments as shown in the
  slide. The generated manifest.mf file in the
  archive should have the information given in
  Simulator.mf (which you write).
• gtjar cfm Simulator.jar Simulator.mf
  StockBroker/Simulator/Stock.class
  StockBroker/Simulator/Helper.class
  StockBroker/Simulator/Price.class
• if the jar options contain both the letters f and
  m, the JAR and manifest files listed in the
  command line should be in the same order. For
  example, if f comes before m, the JAR filename
  should come before the manifest filename.

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Examples

• See Composites using a jar in the Mastermind
  Directory
• See Animation Demo using a jar at
• http//acad.kutztown.edu/spiegel/cis421/Animation
  /AppletJAR/ball.htm
• inner classes specified in a manifest