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

A Manifest File plays very important role in streaming media content. Because it is the one file which tells subscriber end devices what about the streaming content is.

This manifest file contains Resolution of content, Codecs of content and adaptive bitrate.

If still you wants to understand it in details then you can visit this brief article which will make your all confusion clear : What Is Manifest File Explain In Details with Diagram

Answer 2

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.)

Answer 3

The manifest is a special file that can contain information about the files packaged in a JAR file. By tailoring this "meta" information that the manifest contains, you enable the JAR file to serve a variety of purposes.

Mainfest file is mainly known for contains the name of the class that holds the main function, among various classes in the package...

When you create a JAR file, it automatically receives a default manifest file. There can be only one manifest file in an archive, and it always has the pathname

META-INF/MANIFEST.MF

Answer 4

The manifest is a specific no-class file assembled within a Jar, which contains the descriptive pairs of keys and values of this Jar and we usually called it metadata, it tells end users or callers:

what the propose of Jar? who is the writer? when it was created? what is creation env? what is JDK version? and even more...(Assuming have these values in manifest)

Answer 5

Manifest file provides the meta data for a file. The meta data is in form of name-value pairs. In your above example they have provided the MD5 hash of the class file which is calculated without the manifest file. This is a security measure so that if someone modifies the file and adds some hackish code, you can detect it with the signatures.

It plays no role in updating the file.