Download 1 jar-files

1
jar-files
1.1
Summary
Jar files are a way of packaging a java application as a single executable file. A jar file can contain
bytecode (.class files) as well as data files, graphics images and other resources belonging to a java
application.
A jar-file is essentially a zip file with special features. You can easily view the contents of a jar file by
renaming the file to .zip ( or adding the .zip extension) and the use software like WinZip of Windows
XP’s internal. Zip file viewer. Zip tools cannot create jar files! Jar files contains features not
implemented in standard zip tools.
The purpose of this document is to provide a brioef description of jar-files and to provide an example
of how a executable application in the form of a jar file can be created.
1.2
Thje structure of a jar file
The netbeans environment creates jar-files whenever a project is successfully built. This example is
given for the .jar file provided by netbeans building the KeyboardReading example. You find the jar
file in your Project directory in the subdirectory named dist, see below.
The jar-file is renamed with a .zip extension for easy viewing in WinXP.
Thi zip-file displays the package created in the keyboardreading example, keyboardreading.
1.3
The jar manifest
Most of the features provided by the jar format are contained within the folder META-INF. The
META-INF folder contains metadata (information about the jar-file and the application). Nothing
required by the application itself is located within this folder.
The information is containg in a file called MANIFEST.MF. Manifest.mf is a plain text file with the
.mf extension. The format of the Manifest.mf file is defined by jar. Example
This instruction are created by the NetBeans environment. The information in the manifest is linebased key-value pairs.
Manifestets form
NAME: VALUE
The key name/value pairs being
Manifest-Version: 1.0
Main-Class: keyboardreading.KeyboardReading
This provides the java environment with the instructions required to execute the application.
In particular the class containing the public static void main(String[]arg) method.
1.4
Creating jar files
You create a jar file by using the tool jar.exe. jar.exe is a command-line tool located in the java bin
directory. Locate you java installation directory and locate the bin/jar.exe file. You command tool
should have a path set to the java installation directory.
Example 2 the help for creating the .jar file. Execute the command in your environment to get the help
contents given in english.
jar cvfm ApplicationName Mainfest-file Class-files
Suppose we have written an application where the class containing the main method is named
StartClass (of StartClass.class) and the required files, including StartClass.class, are located in
a directory java.
1 – Create the manifest file using Notepad or similar suitable tool. The manifest must contain at a
minimum.
Manifest-Version: 1.0
Main-Class: StartClass
Create this file in the same directory as the class files.
2 – Type the following command while in the directory java/
jar cvfm MyApplication.jar manifest.txt *.class
The order of cvfm is important. c-create, v-verbose, f-file (supply a filename for the application/jar
file), m-manifest(add a given manifest file).
Something similar to the above will display..
The jar tool creates a file MyApplication.jar. You can execute this application by issuing the command
java –jar MyApplication.jar
1.4.1
Configuring windows to execute –jar files
You java install procedure may already have provoded you with this particular feature. If this is the
case you shold not execute these instructions.
In the explorer interface select menu Tools – select Folder Options – select tab File Types – select
New... type jar and Ok.
With the jar filetype selected select Advanced
If the open action is nonexistent select New… If it exist select Edit…
In the edit field Application used … navigate to your java installation directory. Select the java
interpreter javaw.exe. Add the parameters -jar "%1" %*
"C:\Program Files\Java\jre1.5.0_05\bin\javaw.exe" -jar "%1" %*
or
"C:\Program Files\Java\jre1.5.0_05\bin\java.exe" -jar "%1" %*
Java.exe should be used if you would like to be able to execute console based applications.
This will associate .jar files with the java runtime environment. Now your .jar files will be
executable. You can execute you jar application file by double-clicking your .jar file or by
writing
start MyApplication.jar
or just
MyApplication.jar
At a command prompt. The first statement will execute the application in a new process(own
window in the console case), the second executes the application in the same console.