What is the purpose of Manifest file

Question

http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html

What does a manifest file do? What is the purpose of it?

Manifest-Version: 1         


        

Answer 1

What does a manifest file do? What is the purpose of it?

The purpose is to hold metadata about the JAR file and the classes that it contains. The metadata is used for a variety of things, including tracking the origin of the JAR, protecting against tampering, and providing the extra information needed for an executable JAR.

The link in your question is broken. Here are a couple of alternatives:

• Working with Manifest Files: The Basics
• JAR File Specification

Does it update these classes in the jar automatically if there any changes in the server?

No.

Those entries are part of a scheme for detecting tampering with JAR files; e.g. someone replacing those classes with modified versions. (The other parts of the scheme are a digital signature of the hashes, and stuff in the launcher that checks the signatures and hashes before launching.)