Jar - the Archive Tool

Introducing jar

jar - creates an archive for classes and resources, and can manipulate or restore individual classes or resources from an archive. The jar command is a general-purpose archiving and compression tool, based on the ZIP and ZLIB compression formats.

Synopsis

jar [OPTION...] [ [--release VERSION] [-C dir] files] ...

Description

The jar command is a general-purpose archiving and compression tool, based on the ZIP and ZLIB compression formats. Initially, the jar command was designed to package Java applets (not supported since JDK 11) or applications; however, beginning with JDK 9, users can use the jar command to create modular JARs. For transportation and deployment, it’s usually more convenient to package modules as modular JARs.

The syntax for the jar command resembles the syntax for the tar command. It has several main operation modes, defined by one of the mandatory operation arguments. Other arguments are either options that modify the behavior of the operation or are required to perform the operation.

When modules or the components of an application (files, images, and sounds) are combined into a single archive, they can be downloaded by a Java agent (such as a browser) in a single HTTP transaction, rather than requiring a new connection for each piece. This dramatically improves download times. The jar command also compresses files, which further improves download time. The jar command also enables individual entries in a file to be signed so that their origin can be authenticated. A JAR file can be used as a class path entry, whether or not it’s compressed.

An archive becomes a modular JAR when you include a module descriptor, module-info.class, in the root of the given directories or in the root of the JAR archive. The following operations described in Operation Modifiers Valid Only in Create and Update Modes are valid only when creating or updating a modular JAR or updating an existing non-modular JAR:

• --module-version

• --hash-modules

• --module-path

Main Operation Modes

When using the jar command, you must specify the operation for it to perform. You specify the operation mode for the jar command by including the appropriate operation arguments described in this section. You can mix an operation argument with other one-letter options. Generally the operation argument is the first argument specified on the command line.

-c or --create Creates the archive.

-i=FILE or --generate-index=FILE Generates index information for the specified JAR file.

-t or --list Lists the table of contents for the archive.

-u or --update Updates an existing JAR file.

-x or --extract Extracts the named (or all) files from the archive.

-d or --describe-module Prints the module descriptor or automatic module name.

Operation Modifiers Valid in Any Mode

You can use the following options to customize the actions of any operation mode included in the jar command.

-C directory Changes the specified directory and includes the files specified at the end of the command line:

jar [OPTION...] [ [--release VERSION] [-C dir] files]

-f=FILE or --file=FILE Specifies the archive file name.

--release VERSION Creates a multi-release JAR file. Places all files specified after the option into a versioned directory of the JAR file named META-INF/versions/VERSION/, where VERSION must be a positive integer whose value is 9 or greater.

At run time, where more than one version of a class exists in the JAR, the JDK will use the first one it finds, searching initially in the directory tree whose VERSION number matches the JDK's major version number. It will then look in directories with successively lower VERSION numbers, and finally look in the root of the JAR.

-v or --verbose Sends or prints verbose output to standard output.

Operation Modifiers Valid Only in Create and Update Modes

You can use the following options to customize the actions of the create and the update main operation modes:

-e=CLASSNAME or --main-class=CLASSNAME Specifies the application entry point for standalone applications bundled into a modular or executable modular JAR file.

-m=FILE or --manifest=FILE Includes the manifest information from the given manifest file.

-M or --no-manifest Doesn’t create a manifest file for the entries.

--module-version=VERSION Specifies the module version, when creating or updating a modular JAR file, or updating a non-modular JAR file.

--hash-modules=PATTERN Computes and records the hashes of modules matched by the given pattern and that depend upon directly or indirectly on a modular JAR file being created or a non-modular JAR file being updated.

-p path or --module-path path Specifies the location of module dependence for generating the hash.

@file Reads jar options and file names from a text file.

Operation Modifiers Valid Only in Create, Update, and Generate-index Modes

You can use the following options to customize the actions of the create (-c or --create) the update (-u or --update) and the generate-index (-i or --generate-index=FILE) main operation modes:

-0 or --no-compress Stores without using ZIP compression.

Other Options

The following options are recognized by the jar command and not used with operation modes:

-h or --help[:compat] Displays the command-line help for the jar command or optionally the compatibility help.

--help-extra Displays help on extra options.

--version Prints the program version.

Examples of jar Command Syntax

Examples of jar Command Syntax

Create an archive, classes.jar, that contains two class files, Foo.class and Bar.class.

jar --create --file classes.jar Foo.class Bar.class

Create an archive, classes.jar, by using an existing manifest, mymanifest, that contains all the files in the directory foo/.

jar --create --file classes.jar --manifest mymanifest -C foo/

Create a modular JAR archive, foo.jar, where the module descriptor is located in classes/module-info.class.

jar --create --file foo.jar --main-class com.foo.Main --module-version 1.0 -C foo/classes resources

Update an existing non-modular JAR, foo.jar, to a modular JAR file.

jar --update --file foo.jar --main-class com.foo.Main --module-version 1.0 -C foo/module-info.class

Create a versioned or multi-release JAR, foo.jar, that places the files in the classes' directory at the root of the JAR, and the files in the classes-16 directory in the META-INF/versions/16 directory of the JAR. In this example, the classes/com/foo directory contains two classes, com.foo.Hello (the entry point class) and com.foo.NameProvider, both compiled for JDK 8. The classes-16/com/foo directory contains a different version of the com.foo.NameProvider class, this one containing JDK 16 specific code and compiled for JDK 16.

Given this setup, create a multi-release JAR file foo.jar by running the following command from the directory containing the directories classes and classes-16.

jar --create --file foo.jar --main-class com.foo.Hello -C classes . --release 16 -C classes-16 .

The JAR file foo.jar now contains:

jar -tf foo.jar

META-INF/ 
META-INF/MANIFEST.MF 
com/ 
com/foo/ 
com/foo/Hello.class 
com/foo/NameProvider.class 
META-INF/versions/16/com/ 
META-INF/versions/16/com/foo/ 
META-INF/versions/16/com/foo/NameProvider.class

As well as other information, the file META-INF/MANIFEST.MF, will contain the following lines to indicate that this is a multi-release JAR file with an entry point of com.foo.Hello.

...
Main-Class: com.foo.Hello
Multi-Release: true

Assuming that the com.foo.Hello class calls a method on the com.foo.NameProvider class, running the program using JDK 16 will ensure that the com.foo.NameProvider class is the one in META-INF/versions/16/com/foo/. Running the program using JDK 8 will ensure that the com.foo.NameProvider class is the one at the root of the JAR, in com/foo.

Create an archive, my.jar, by reading options and lists of class files from the file classes.list.

jar --create --file my.jar @classes.list