Creating an Executable Jar File
In Java, it is common to combine several
classes in one .jar ("java archive") file.
Library classes are stored that way.
Larger projects use jar files.
You can create your own jar file combining several classes, too.
jar files are created using the
jar.exe
utility program from
the JDK.
You can make your jar file runnable by telling jar.exe
which
class has main
.
To do that, you need to create a manifest file.
A manifest is a one-line text file with a "Main-Class" directive.
For example:
Main-Class: Craps
This line must end with a newline.
A jar file created with a main class manifest can be used both
as a library and a runnable jar.
If you use it as a library, you can edit and compile
any of the classes included in the jar, and add it to
your project.
Then it will override the one in the jar file.
You can create a manifest file in any text editor,
or even by using the MS-DOS
echo
command.
You can give your manifest file any name, but it's better
to use something standard, such as manifest.txt
.
Once you have a manifest and all your classes
have been compiled, you need to run JDK's
jar.exe
utility.
It is located in the JDK’s bin
folder, the same place
where javac.exe
and java.exe
are.
jar.exe
takes command-line arguments;
if you run it without any arguments, it will
display the usage information and examples.
You need
C\mywork> jar cvfm MyJarName.jar manifest.txt *.class
cvfm
means "create a jar;
show verbose output;
specify the output jar file name;
specify the manifest file name."
This is followed by the name you wish to give to your jar file,
the name of your manifest file, and the list of
.class
files
that you want included in the jar.
*.class
means all class files in the current directory.
Actually, if your manifest contains only the Main-Class directive,
you can specify the
main
class directly on the jar.exe
's
command line, using the e
switch, instead of m
.
Then you do not need a separate manifest file; jar
will
add the required manifest to your jar file for you.
For example:
C\mywork> jar cvfe MyJarName.jar MyMainClass *.class
Below is a reference for creating a jar file in Eclipse
and the detailed steps for doing this
in Command Prompt and in JCreator.
Creating a jar File in Eclipse
In Eclipse Help contents, expand "Java development user guide" ==> "Tasks" ==> "Creating JAR files." Follow the instructions for "Creating a new JAR file" or "Creating a new runnable JAR file."
The
JAR File
and Runnable JAR File
commands
are for some reason located under the File
menu:
click on Export...
and expand the Java
node.
Creating a jar File in JCreator
You can configure a "tool" that will automate the jar creation process. You only need to do it once.- Click on
Configure/Options
. - Click on
Tools
in the left column. - Click
New
, and chooseCreate Jar file
. - Click on the newly created entry
Create Jar File
in the left column underTools
. - Edit the middle line labeled
Arguments:
it should havecvfm $[PrjName].jar manifest.txt *.class
- Click OK.
Now set up a project for your program,
create a manifest file
manifest.txt
or copy
and edit an existing one.
Place manifest.txt
in the same folder
where the .class
files go.
Under View/Toolbars
check the Tools
toolbar.
Click on the corresponding tool button or press Ctrl-1
(or Ctrl-n
if this is the n-th tool)
to run the Create Jar File
tool.
With Windows Explorer, go to the jar file
that you just created and double click on it to run.
Creating a jar File in Command Prompt
- Start Command Prompt.
- Navigate to the folder that holds your class files:
C:\>cd \mywork
- Set path to include JDK’s bin.
For example:
C:\mywork> path c:\Program Files\Java\jdk1.7.0_25\bin;%path%
- Compile your class(es):
C:\mywork> javac *.java
- Create a manifest file and your jar file:
C:\mywork> echo Main-Class: Craps >manifest.txt
C:\mywork> jar cvfm Craps.jar manifest.txt *.class
orC:\mywork> jar cvfe Craps.jar Craps *.class
- Test your jar:
C:\mywork> Craps.jar
orC:\mywork> java -jar Craps.jar
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