Download Creating Jar Files

Creating Jar Files
Jin Hung, Gregory Olds, George Blank,
Sun Java Web Site
What is a Jar File?
• Java archive (jar) files are compressed files that
can store one or many files.
• Jar files normally contain java or class files, but
other files may also be included.
• Jar files can be run on Windows by double
clicking jar files if the JVM is installed.
Why use a JAR File?
• Compression:Jar files reduce the size of the original files.
• Speed: The applet can be downloaded in one http
transaction.
• Security: Jar files can be signed digitally. Users who
recognize the signature can optionally grant permission to
run the file or refuse.
• Package sealing: Sealing a package within the jar file
means that all classes defined in that package are found
in the same jar file.
Flow Chart
• Create a manifest.mf file
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•
•
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•
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Create a jar file
Basic jar commands
JAR subdirectories
Execute the jar file
Common mistakes
Bibliography
How to create a jar file:
Simple Method
• The jar command a utility that comes with the
JDK.
• The format of the basic format of the jar
command is:
Jar cf jar-file input-files
How to create a jar file
• Take as an example the Java application
made from the files
– Foo.class
– Foobar.class
• To make a jar file use the command
Jar cvf Foo.jar Foo.class Foobar.class
• Note that each file is separated by a space
How to create a jar file
• The execution of this command creates the
file:
– Foo.jar
Executing Jar Application
• Jar applications can be run with the following
basic command:
– java -jar jar-file
• So to run our Foo.jar if it was an application
use:
– java -jar Foo.jar
Executing Jar Application
• Many Operating systems such as the Mac OS
will allow the execution of jar applications by
simply double clicking on them.
Executing Jar Applets
• Applets are invoked from applet tags in HTML
code.
• To execute an Applet simply add the name of
the jar file into the applet tag is under the
archive parameter.
Executing Jar Applets
• For example, using the applet tag for your
Foo.jar archive, you would use the following:
<applet code=TicTacToe.class
archive=”Foo.jar"
width=120 height=120>
</applet>
Creating Jar Files:
Advanced method
• The more formal and complete way to create
a jar file is described in the following slides.
• Note that the more complex your process, the
more difficulty a beginning Java user is going
to have with it.
Create manifest.mf
• Create a new notepad file named manifest.mf. This file
contains a signal line that points out the main class. Here
is the signal line.
Main-Class:<Space>name of main class
<blank line>
 Blank line must be included because some Windows OS
versions need it.
For example: myClass is my main Class. So manifest.mf is
following.
Main-Class: myClass
<blank line is here>
Jar file and Jar Commands
• Next, create a jar file using the “jar” command in java.
Here is the command.
jar cvmf <the jar file name>.jar manifest.mf
A.class B.class……..
There are spaces between each file and class name.
 Here are the basic jar commands
Create Jar file => jar cf jar-file input-file
View Jar file => jar tf jar-file
Extract Jar file => jar xf jar-file
JAR Subdirectories
• The JAR format also support storing files in a
directory structure. Consider the following
structure.
• Note: CS 602 students have had a lot of
difficulty getting files to work in subdirectories. If you have trouble, put all your
files in your default Web directory.
JAR Subdirectories
JAR Subdirectories
• If we want to keep the same structure, we can
compress files by typing:
jar cmf Sample.mf Sample.jar Sample.class
Turtle.class Sample.java Turtle.java images
JAR Subdirectories
• The contents listing appears as:
META-INF/
META-INF/MANIFEST.MF
Sample.class
Turtle.class
Sample.java
Turtle.java
images/ images/image1.gif
images/image2.gif
images/image3.gif
Executing the Jar File
• There are two ways to execute jar files.
• 1. If an OS can read *.jar as javaw.exe or
java.exe, users can double click jar files on
the window. Otherwise:
• 2. In a command window, type in
java –jar jar-file
Common Mistakes
• Forgetting to leave a blank line after the main class
declaration in the manifest.mf. OS may return “Fail to
load Main-Class manifest attribute” error in Windows
machines.
• Failing to compress all your files. You have to type in
all the files you want to compress. Separate these
files with a space.
Bibliography
• Xiaoping Jia, Object-Oriented Software
Development Using Java, Addison Wesley,
2nd Edition, 2003.
• Packaging Programs in JAR Files, and
Running JAR-Packaged Software
http://java.sun.com/docs/books/tutorial/deploy
ment/jar/index.html