Download Creating Jar Files

 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.
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.

 Create
a manifest.mf file
 Create a jar file
 Basic jar commands
 JAR subdirectories
 Execute the jar file
 Common mistakes
 Bibliography
 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
 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
 The execution of this command creates the
file:

Foo.jar
 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
Many Operating systems such as the Mac OS will allow the
execution of jar applications by simply double clicking
on them.
 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.
 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>
 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 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>


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
 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.
 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

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
 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
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.
