What is the file format of jar?

jar is a software package file format, usually used to aggregate a large number of Java class files, related metadata and resource (text, images, etc.) files into one file; JAR file is an archive file. Built in ZIP format, with ".jar" as the file extension.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

In the software field, JAR file (Java Archive, English: Java Archive) is a software package file format that is usually used to aggregate a large number of Java class files, related metadata and resources (text, pictures, etc. ) file to a file for developing Java platform applications or libraries.

A JAR file is an archive file built in ZIP format with a .jar file extension. Users can use the JDK's own jar command to create or extract JAR files. You can also use other zip compression tools, but the order of entries in the zip file header is important when compressing, because the Manifest file often needs to be placed first. File names within JAR files are Unicode text.

The JAR file format is based on the popular ZIP file format. Unlike ZIP files, JAR files are not only used for compression and distribution, but also for deployment and packaging of libraries, components and plug-ins, and can be used directly by tools like compilers and JVM. Special files, such as manifests and deployment descriptors, are included in a JAR to instruct tools on how to process a particular JAR.

Features:

• Security

  You can add digital signatures to the contents of JAR files. This way, a tool that recognizes the signature can selectively grant you software security privileges that no other file can, and it can also detect whether the code has been tampered with.

• Reduce download time

  If an applet is bundled into a JAR file, the browser can download the applet's class files and related files in an HTTP transaction resources instead of opening a new connection for each file.

• Compression

  The JAR format allows you to compress files for greater storage efficiency.

• Transport Platform Extensions

  The Java Extensions Framework provides a way to add functionality to the Java core platform. These extensions are packaged in JAR files (Java 3D and JavaMail are examples of extensions developed by Sun).

• Package Sealing

  Packages stored in JAR files can optionally be sealed for enhanced version consistency and security. Sealing a package means that all classes in the package must be found in the same JAR file.

• Package Versioning

  A JAR file can contain data about the files it contains, such as vendor and version information.

• Portability

  The mechanism for handling JAR files is a standard part of the Java platform core API.

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