Can you explain what a JAR metadata file is and what it is used for?

A JAR manifest file is a file named MANIFEST.MF located inside the JAR archive in the META-INF folder. It contains metadata about the contents of the JAR file, such as the version, the main class to launch (Main-Class), dependencies, and other parameters.

This file is used by the JVM and build tools to correctly load and execute the application. For example, specifying the main class allows the JAR to be run as an executable with the command java -jar app.jar.

An example of MANIFEST.MF content:

Manifest-Version: 1.0
Main-Class: com.example.Main
Class-Path: lib/dependency.jar