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 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>

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: name of main class  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

Jar file and Jar Commands Next, create a jar file using the “jar” command in java. Here is the command. jar cvmf.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 sub- directories. If you have trouble, put all your files in your default Web directory.

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, Packaging Programs in JAR Files, and Running JAR-Packaged Software ment/jar/index.html ment/jar/index.html