Creating Jar Files. Based on slides by: Jin Hung, Gregory Olds, George Blank, Sun Java Web Site

Transcription

1 Creating Jar Files Based on slides by: Jin Hung, Gregory Olds, George Blank, Sun Java Web Site

2 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.

3 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.

4 Flow Chart Create a manifest.mf file Create a jar file Basic jar commands JAR subdirectories Execute the jar file Common mistakes Bibliography

5 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

6 Executing Jar Application Many Operating systems such as the Mac OS will allow the execution of jar applications by simply double clicking on them.

7 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.

8 Executing Jar Applets For example, using the applet tag for your Foo.jar archive, you would use the following: <applet code=tictactoe.class </applet> archive= foo.jar" width=120 height=120>

9 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.

10 Create manifest.mf Create a new notepad file named manifest.mf. This file contains two lines that define the author and the main class and a third line that is blank: Created By:<space>Name ( student number ) Main-Class:<Space>name of main class <blank line> For example: for the demo program manifest.mf is: Created By: Hugh Murrell ( ) Main-Class: BigIntegerDemo <blank line>

11 Jar file and Jar Commands Next, create a jar file using the jar command in java. Here is the command. jar cvfm <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

12 JAR Subdirectories The JAR format also support storing files in a directory structure. Consider the following structure:

13 JAR Subdirectories

14 JAR Subdirectories If we want to keep the same structure, we can compress files by typing: jar cvfm Sample.jar Sample.mf Sample.class Turtle.class Sample.java Turtle.java images

15 JAR Subdirectories -3 / 2.:: : /. - /.. :

16 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

17 Viewing manifest information To view then contents of your manifest file I will issue the shell command: unzip p demo.jar META-INF/MANIFEST.MF the p option for unzip causes output to be sent to the console.

18 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.

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