Updating a jar file
See the section on Understanding the Manifest for information about special headers.) You would first prepare a text file containing the headers that you wish to add to the default manifest.
If manually, a JAR file is really just a ZIP file, so you should be able to open it with any ZIP reader.
It's a lot more important when we start to deal with more advanced JAR functionality, such as signing and authenticating JAR files.
Now that you have a base foundation of knowledge of the JAR format, let's address some of that advanced functionality now.
This tool is provided by the Java Development Kit (JDK)We use jar cf command to create this file.
Syntax –With the help of this article, you can create, view, extract, update, and run JAR files in Java.
Paths in JAR files are always relative; you'll never see a path beginning with 68 Thu Nov 01 PDT 2012 META-INF/MANIFEST.
All pathnames are displayed with forward slashes, regardless of the platform or operating system you're using.
As you can see, manifest entries take the form of name-value pairs, using the form: "headername: value".
The manifest file does not really play a role for basic JAR functionality.
Such type of files is used in the JAR file for making it executable.
It used for collecting additional files associated with the components. These types of files are mainly used for implementing libraries.