Jar Archiving

Jussi Pohjolainen

Tampere Polytechnic University of Applied Sciences » ICT

Intro to Jar packaging

• Java Archive File (JAR)
• Archives multiple files into a single file
• Why JAR?
  • Security
  • Decreased download time
  • Compression
  • Package sealing
  • Package versioning

Using JAR-files

• JAR-files are just ZIP-files!
  • For example, it is possible to decompress .jar file with winzip
• Basic operations
  • jar cf my.jar foo.class bar.class - Creating
  • jar tf my.jar - View contents
  • jar xf my.jar - Extract contents
  • java -jar my.jar - Run app

Creating a JAR-file

• Format: jar cf jar-file input-file(s)
  • c - creates a new archive
  • f - spesify archive name
• In practice: jar cf MyJar.jar MyClass.class1 MyClass2.class
• The command generates a default manifest - file for the JAR archive (We'll discuss this later)

        v - Tells the name of each file it's added to the JAR-file
        0 - Store only, does not use ZIP compressioin
        M - Does not create default manifest file
        m - Includes given manifest file
        

Example creating JAR-file

• Java-Swing App contains several files:
  • Application.class - Starts the app
  • MyWindow.class - App's Window
  • MyWindow$1.class - Event Handling (Inner Class)
  • bird.png - Bird's picture
  • birdpeck.png - Bird pecking picture
• Archiving all the files into a single JAR

  jar cvf BirdApp.jar *.class *.png
  added manifest
  adding: Application.class(in = 428) (out= 321)(deflated 25%)
  adding: MyWindow$1.class(in = 556) (out= 377)(deflated 32%)
  adding: MyWindow.class(in = 1289) (out= 774)(deflated 39%)
  adding: bird.png(in = 8059) (out= 7976)(deflated 1%)
  adding: birdpeck.png(in = 8552) (out= 8472)(deflated 0%)
  

META-INF/MANIFEST.MF
Application.class
MyWindow.class
MyWindow$1.class
bird.png
birdpeck.png

Showing contents and extracting

• Contents: jar tf jar-file
• Example:

  • jar tf BirdApp.jar
    META-INF/
    META-INF/MANIFEST.MF
    Application.class
    MyWindow$1.class
    MyWindow.class
    bird.png
    birdpeck.png
    		

• Extracting: jar xf jar-file

Running JAR file (as App)

• Basic command: java -jar jar-file
• This command works only if entry point is defined in the JAR-file's manifest
• Entry point? The class that has your main-method
• You have to update or create your own manifest file..

Intro to Manifest files

• Electronic signing, version control and package sealing is defined in manifest file
• Manifest file gives information about the files in the JAR package
• File is saved in META-INF/MANIFEST.MF path of your JAR package
• Default manifest file contains:

  • Manifest-Version: 1.0
    Created-By: 1.5.0_01 (Sun Microsystems Inc.)
    

• Consists of header: value pairs.

Creating your own manifest file

• Create manifest-file with some text-editor.
• Give command jar cfm jar-file manifestfile input-file(s)
• Manifest file must be encoded using UTF-8

Example

• Create manifest.txt file that contains

  • Main-Class: Application
    

• Important: Manifest-file must end with return ("\n")!
• Create jar-package: jar cfm BirdApp.jar manifest.txt *.class *.png
• This creates JAR file with following contents.

  • Manifest-Version: 1.0
    Created-By: 1.5.0_01 (Sun Microsystems Inc.)
    Main-Class: Application
    

• Run the app java -jar BirdApp.jar

Files

• JarExample.java
• Manifest.txt
• bird.png
• birdpeck.png