Using jar utility in Java - A jar tutorial

By: Emiley J Emailed: 1768 times Printed: 2515 times    

Latest comments
By: rohit kumar - how this program is work
By: Kirti - Hi..thx for the hadoop in
By: Spijker - I have altered the code a
By: ali mohammed - why we use the java in ne
By: ali mohammed - why we use the java in ne
By: mizhelle - when I exported the data
By: raul - no output as well, i'm ge
By: Rajesh - thanx very much...
By: Suindu De - Suppose we are executing

The jar tool combines multiple files into a single JAR archive file. jar is a general-purpose archiving and compression tool, based on ZIP and the ZLIB compression format. However, jar was designed mainly to facilitate the packaging of java applets or applications into a single archive. When the components of an applet or application (.class files, images and sounds) are combined into a single archive, they may be downloaded by a java agent (like a browser) in a single HTTP transaction, rather than requiring a new connection for each piece. This dramatically improves download times. jar also compresses files and so further improves download time. In addition, it allows individual entries in a file to be signed by the applet author so that their origin can be authenticated. The syntax for the jar tool is almost identical to the syntax for the tar command. A jar archive can be used as a class path entry, whether or not it is compressed.

Typical usage to combine files into a jar file is:

C:\Java> jar cf myFile.jar *.class

In this example, all the class files in the current directory are placed into the file named "myFile.jar". A manifest file entry named META-INF/MANIFEST.MF is automatically generated by the jar tool and is always the first entry in the jar file. The manifest file is the place where any meta-information about the archive is stored as name : value pairs.

To add all the files in a particular directory to an archive (overwriting contents if the archive already exists). Enumerating verbosely (with the v option) will tell you more information about the files in the archive, such as their size and last modified date.

C:\Java> dir

12/09/96  12:20a        <DIR>          .    
12/09/96  12:17a        <DIR>          ..  
12/09/96  12:18a                   946 1.au
12/09/96  12:18a                 1,039 2.au
12/09/96  12:18a                   993 3.au
12/09/96  12:19a                48,072 spacemusic.au
12/09/96  12:19a                   527 at_work.gif
12/09/96  12:19a                12,818 monkey.jpg
12/09/96  12:19a                16,242 Animator.class
12/09/96  12:20a                 3,368 Wave.class

              10 File(s)        91,118 bytes

C:\Java> jar cvf bundle.jar *

adding manifest
adding: 1.au
adding: 2.au
adding: 3.au
adding: Animator.class
adding: Wave.class
adding: at_work.gif
adding: monkey.jpg
adding: spacemusic.au

If you already have separate subdirectories for images, audio files and classes, you can combine them into a single jar file:

C:\Java> dir

12/09/96  12:11a        <DIR>          .
12/09/96  12:17a        <DIR>          ..
12/03/96  06:54p        <DIR>          audio
12/06/96  02:02p        <DIR>          images
12/09/96  12:10a        <DIR>          classes

               5 File(s)        207,360 bytes

C:\Java> jar cvf bundle.jar audio classes images

adding: audio/1.au
adding: audio/2.au
adding: audio/3.au
adding: audio/spacemusic.au
adding: classes/Animator.class
adding: classes/Wave.class
adding: images/monkey.jpg
adding: images/at_work.gif

C:\Java> dir 

12/09/96  12:11a        <DIR>          .
12/09/96  12:17a        <DIR>          ..
12/09/96  12:11a               207,360 bundle.jar
12/03/96  06:54p        <DIR>          audio
12/06/96  02:02p        <DIR>          images
12/09/96  12:10a        <DIR>          classes

               6 File(s)        207,360 bytes

To see the entry names in the jarfile, use the "t" option:

C:\Java> jar tf bundle.jar

META-INF/
META-INF/MANIFEST.MF
audio/1.au
audio/2.au
audio/3.au
audio/spacemusic.au
classes/Animator.class
classes/Wave.class
images/monkey.jpg
images/at_work.gif

To add an index file to the jar file for speeding up class loading, use the -i option.

Let's say you split the inter-dependent classes for a stock trade application, into three jar files:  main.jar, buy.jar, and sell.jar. If you specify the Class-path attribute in the main.jar manifest as:
Class-Path: buy.jar sell.jar
then you can use the -i option to speed up your application's class loading time:
C:\Java> jar i main.jar
An INDEX.LIST file is inserted to the META-INF directory which will enable the application class loader to download the specified jar files when it is searching for classes or resources.

Java Home | All Java Tutorials | Latest Java Tutorials

Sponsored Links

If this tutorial doesn't answer your question, or you have a specific question, just ask an expert here. Post your question to get a direct answer.



Bookmark and Share

Comments(0)


Be the first one to add a comment

Your name (required):


Your email(required, will not be shown to the public):


Your sites URL (optional):


Your comments:



More Tutorials by Emiley J
Password must include both numeric and alphabetic characters - Magento
What is Hadoop?
Returning multiple values from a web service
Tomcat and httpd configured in port 8080 and 80
Java Webservices using Netbeans and Tomcat
Java WebService connected to Database
How to Deploy a Java Web Service
Call a webservice in Java
Java WebService - Create your first web service in Java
package javax.jws does not exist
Getting Started with Android
HTML5 Location - getCurrentPosition() in HTML5
HTML5 Canvas - Using Canvas in HTML5
HTML5 - Introduction
HTML5 Video - Handling video in HTML5

More Tutorials in Java
Update contents of a file within a jar file
Tomcat and httpd configured in port 8080 and 80
Java File
Java String
Count number of vowels, consonants and digits in a String in Java
Reverse a number in Java
Student marks calculation program in Java
Handling Fractions in Java
Calculate gross salary in Java
Calculate average sale of the week in Java
Vector in Java - Sample Program
MultiLevel Inheritance sample in Java
Multiple Inheritance sample in Java
Java program using Method Overriding
Java program to check if user input is an even number

More Latest News
Most Viewed Articles (in Java )
InetAddress Example program in Java
Read from a COM port using Java program
Stack example in Java - push(), pop(), empty(), search()
How to use ArrayList in Java
The Basic Structure of a Simple Java program
Using StringTokenizer in Java
FileReader and FileWriter example program in Java
Transient vs Volatile modifiers in Java
Vector example in Java
Method Overriding in Java
Method Overloading (function overloading) in Java
instanceof sample program in Java
append() in Java
Student marks calculation program in Java
Reading from a file and writing to a file using Java program
Most Emailed Articles (in Java)
Text to Speech conversion program in Java
inheritance in Java
How to initialize an Array and how to copy the array
Using Charts in JasperReports
What is Unicode?
Operator Precedence in Java
Of Object, equals (), == and hashCode ()
DateFormat sample program in Java
A Simple whois program in Java
PushbackReader sample program in Java
CharArrayReader example program in Java
ByteArrayOutputStream - sample program in Java
Vector example in Java
Arrays example in Java - asList(), binarySearch(), fill(), sort(), equals()
HashSet Sample program in Java