Modifying a Manifest File

You can modify the contents of a JAR file in 2 ways:

Use the m option to add custom information to the manifest during creation of a JAR file. The m option is described in this section.
Use the u option to update the contents of an existing JAR file, including its manifest.

The u option is covered in the section called Updating a JAR File.

The Jar tool puts a default manifest with pathname META-INF/MANIFEST.MF into any JAR file you create.
You can add JAR file functionality, such as specifying an entry point, by modifying the default manifest.
The m option allows you to add information to the default manifest while creating a JAR file.
First, create a text file, manifest-addition, with the information you wish to add (see Example below).
The basic command has this format:

jar cmf manifest-addition jar-file input-file(s)

The options and arguments used in this command:

The m option indicates that you want to merge information from an existing manifest file into the manifest file of the JAR file you're creating.
manifest-addition is the name (or path/name) of the existing text file whose contents you want included in the JAR file's manifest.

Example

To indicate which class is the project's entry point, add a Main-Class header to the JAR file's manifest. The header takes the form:
Main-Class: classname

The header's value, classname, is the name of the class that's the project's entry point.

Prepare a text file, say manifest-addition consisting of the line with the Main-Class header and value.
For example, if your project's main class is Main, your text file has this line:

Main-Class: Main

Merge the information in file manifest-addition into a JAR file's manifest:

jar cmf manifest-addition <project_name>.jar class

where class is the directory with your class files.

You now can run your project from the command line:

java -jar <project_name>.jar

Warning: The manifest text file must end with a new line or carriage return.

Exercise

Make a file indicating that teamname.projectname.Main is the entry point for your project.
Modify the jar command that creates the projectname.jar so that it includes this manifest information.
Give a command to run your project, given the projectname.jar file.