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{{Short description|Java archive file format}}
{{Distinguish|text=[[JAR (software)|JAR]] – file compression software and its format; see also [[Jar (disambiguation)]]}}
{{More citations needed|date=June 2008}}

{{Infobox file format
{{Infobox file format
| name = Java Archive
| name = Java Archive
| icon = [[Image:Nuvola mimetypes java jar.png|[[KDE]] JAR file icon]]
| icon = [[Image:Nuvola mimetypes java jar.png|[[KDE]] JAR file icon]]
| iconcaption = [[KDE]] JAR file icon
| extension = <tt>.jar</tt>
| extension = <code>.jar</code>
| mime = application/java-archive<ref>{{cite web|title=File Extension .JAR Details|url=http://filext.com/file-extension/JAR|accessdate=29 November 2012}}</ref><ref>{{cite web|title=MIME : Java Glossary|url=http://mindprod.com/jgloss/mime.html|accessdate=29 November 2012}}</ref>
| mime = application/java-archive<ref>{{cite web|title=File Extension .JAR Details|url=https://filext.com/file-extension/JAR|access-date=29 November 2012}}</ref><ref>{{cite web|title=MIME : Java Glossary|url=http://mindprod.com/jgloss/mime.html|access-date=29 November 2012}}</ref><ref>{{cite web|title=IANA Assignment|url=https://www.iana.org/assignments/media-types/application/java-archive|access-date=12 May 2023}}</ref>
| type code =
| uniform type = com.sun.java-archive
| type code =
| uniform type = com.sun.java-archive
| magic = <code>50 4b 03 04</code> ASCII:PK\x03\x04
| magic = <code>50 4b 03 04</code> ASCII:PK\x03\x04
| owner = [[Netscape]], [[Sun Microsystems]], [[Oracle Corporation]]
| owner = [[Netscape]], [[Sun Microsystems]], [[Oracle Corporation]]
| genre = [[File archive]], [[data compression]]
| genre = [[File archive]], [[data compression]]
| container for =
| container for =
| contained by =
| contained by =
| extended from = [[ZIP (file format)|ZIP]]
| extended from = [[ZIP (file format)|ZIP]]
| extended to =
| extended to =
| standard =
| standard =
| url =
| url =
}}
}}


A '''JAR''' ('''J'''ava '''AR'''chive) is a [[package format|package]] [[file format]] typically used to aggregate many [[Java class file]]s and associated [[metadata]] and resources (text, images, etc.) into one file for distribution.<ref>{{cite web|url=http://java.sun.com/javase/6/docs/technotes/guides/jar/index.html|title=JDK 6 Java Archive (JAR)-related APIs & DeveloperGuides|publisher=}}</ref>
A '''JAR''' ("Java archive") file is a [[package format|package]] [[file format]] typically used to aggregate many [[Java class file]]s and associated [[metadata]] and resources (text, images, etc.) into one file for distribution.<ref>{{cite web|url=http://java.sun.com/javase/6/docs/technotes/guides/jar/index.html|title=JDK 6 Java Archive (JAR)-related APIs & DeveloperGuides}}</ref>


JAR files are [[archive file]]s that include a Java-specific [[manifest file]]. They are built on the [[ZIP (file format)|ZIP format]] and typically have a <code>.jar</code> [[file extension]].<ref>{{cite web| title=JAR File Specification| publisher=Oracle| work=Java SE Documentation| url=http://docs.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#JARIndex| url-status=live| archive-url=https://web.archive.org/web/20170911103525/http://docs.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#JARIndex| archive-date=2017-09-11}}</ref>
JAR files are [[archive file]]s that include a Java-specific [[manifest file]]. They are built on the [[ZIP (file format)|ZIP format]] and typically have a <code>.jar</code> [[file extension]].<ref>{{cite web| title=JAR File Specification| publisher=Oracle| work=Java SE Documentation| url=http://docs.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#JARIndex| url-status=live| archive-url=https://web.archive.org/web/20170911103525/http://docs.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#JARIndex| archive-date=2017-09-11}}</ref>
Line 29: Line 28:
A JAR file may contain a manifest file, that is located at <code>META-INF/MANIFEST.MF</code>. The entries in the manifest file describe how to use the JAR file. For instance, a [[Classpath (Java)|Classpath]] entry can be used to specify other JAR files to load with the JAR.
A JAR file may contain a manifest file, that is located at <code>META-INF/MANIFEST.MF</code>. The entries in the manifest file describe how to use the JAR file. For instance, a [[Classpath (Java)|Classpath]] entry can be used to specify other JAR files to load with the JAR.


== Extraction ==
==Extraction==
The contents of a JAR file may be extracted using any standard decompression software, or the <code>jar</code> command line utility: "<code>jar -xf foo.jar</code>".
The contents of a file may be extracted using any archive extraction software that supports the ZIP format, or the
<code>jar</code> command line utility provided by the Java Development Kit.


== Security ==
==Security==
Developers can [[digital signature|digitally sign]] JAR files. In that case, the signature information becomes part of the embedded manifest file. The JAR itself is not signed, but instead every file inside the archive is listed along with its checksum; it is these checksums that are signed. Multiple entities may sign the JAR file, changing the JAR file itself with each signing, although the signed files themselves remain valid. When the Java runtime loads signed JAR files, it can validate the signatures and refuse to load classes that do not match the signature. It can also support 'sealed' packages, in which the [[Classloader]] will only permit Java classes to be loaded into the same package if they are all signed by the same entities. This prevents malicious code from being inserted into an existing package, and so gaining access to package-scoped classes and data.
Developers can [[digital signature|digitally sign]] JAR files. In that case, the signature information becomes part of the embedded manifest file. The JAR itself is not signed, but instead every file inside the archive is listed along with its checksum; it is these checksums that are signed. Multiple entities may sign the JAR file, changing the JAR file itself with each signing, although the signed files themselves remain valid. When the Java runtime loads signed JAR files, it can validate the signatures and refuse to load classes that do not match the signature. It can also support 'sealed' packages, in which the [[Classloader]] will only permit Java classes to be loaded into the same package if they are all signed by the same entities. This prevents malicious code from being inserted into an existing package, and so gaining access to package-scoped classes and data.


Line 40: Line 40:
An executable Java program can be packaged in a JAR file, along with any libraries the program uses. Executable JAR files have the manifest specifying the [[entry point]] class with <code>Main-Class: myPrograms.MyClass</code> and an explicit Class-Path (and the -cp argument is ignored). Some operating systems can run these directly when clicked. The typical invocation is <code>java -jar foo.jar</code> from a command line.
An executable Java program can be packaged in a JAR file, along with any libraries the program uses. Executable JAR files have the manifest specifying the [[entry point]] class with <code>Main-Class: myPrograms.MyClass</code> and an explicit Class-Path (and the -cp argument is ignored). Some operating systems can run these directly when clicked. The typical invocation is <code>java -jar foo.jar</code> from a command line.


Native launchers can be created on most platforms. For instance, [[Microsoft Windows]] users who prefer having Windows [[EXE]] files can use tools such as [[JSmooth]], Launch4J, WinRun4J or [[Nullsoft Scriptable Install System]] to wrap single JAR files into executables.
Native launchers can be created on most platforms. For instance, Microsoft Windows users who prefer having Windows [[EXE]] files can use tools such as JSmooth, Launch4J, WinRun4J or [[Nullsoft Scriptable Install System]] to wrap single JAR files into executables.


==Manifest==
==Manifest==
A manifest file is a [[metadata]] file contained within a JAR.<ref>{{cite web|url=http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html |title=Understanding the Manifest |publisher=Java.sun.com |date=2003-03-21 |accessdate=2012-07-31}}</ref><ref>{{cite web|url=http://download.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#JAR%20Manifest |title=JAR File Specification |publisher=Download.oracle.com |date= |accessdate=2012-07-31}}</ref> It defines extension and package-related data. It contains [[name-value pair]]s organized in sections. If a JAR file is intended to be used as an executable file, the manifest file specifies the main class of the application. The manifest file is named <code>MANIFEST.MF</code>. The manifest directory has to be the first entry of the compressed archive.
A manifest file is a [[metadata]] file contained within a JAR.<ref>{{cite web|url=http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html |title=Understanding the Manifest |publisher=Java.sun.com |date=2003-03-21 |access-date=2012-07-31}}</ref><ref>{{cite web|url=http://download.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#JAR%20Manifest |title=JAR File Specification |publisher=Download.oracle.com |access-date=2012-07-31}}</ref> It defines extension and package-related data. It contains [[name–value pair]]s organized in sections. If a JAR file is intended to be used as an executable file, the manifest file specifies the main class of the application. The manifest file is named <code>MANIFEST.MF</code>. The manifest directory has to be the first entry of the compressed archive.


===Specifications===
===Specifications===
The manifest appears at the [[Canonical form|canonical]] location <code>META-INF/MANIFEST.MF</code>.<ref name="jarspec">{{cite web|url=https://docs.oracle.com/javase/10/docs/specs/jar/jar.html |title=JAR File Specification |publisher=Download.oracle.com |date= |accessdate=2012-07-31}}</ref> There can be only one manifest file in an archive and it must be at that location.
The manifest appears at the [[Canonical form|canonical]] location <code>META-INF/MANIFEST.MF</code>.<ref name="jarspec">{{cite web|url=https://docs.oracle.com/javase/10/docs/specs/jar/jar.html |title=JAR File Specification |publisher=Download.oracle.com |access-date=2012-07-31}}</ref> There can be only one manifest file in an archive and it must be at that location.


The content of the manifest file in a JAR file created with version 1.0 of the [[Java Development Kit]] is the following.
The content of the manifest file in a JAR file created with version 1.0 of the [[Java Development Kit]] is the following.
Line 60: Line 60:


Most uses of JAR files go beyond simple archiving and compression and require special information in the manifest file.
Most uses of JAR files go beyond simple archiving and compression and require special information in the manifest file.

===Features===
The manifest allows developers to define several useful features for their jars. Properties are specified in key-value pairs.


====Applications ====
====Applications ====
If an application is contained in a JAR file, the [[Java Virtual Machine]] needs to know the application's entry point. An entry point is any class with a <code>public static void main(String[] args)</code> method. This information is provided in the Main-Class header, which has the general form:
If an application is contained in a JAR file, the [[Java virtual machine|Java Virtual Machine]] needs to know the application's entry point. An entry point is any class with a <code>public static void main(String[] args)</code> method. This information is provided in the manifest Main-Class header, which has the general form:


Main-Class: com.example.MyClassName
Main-Class: com.example.MyClassName
Line 72: Line 75:


To seal a package, a Name entry needs to appear, followed by a Sealed header, such as:
To seal a package, a Name entry needs to appear, followed by a Sealed header, such as:
<source lang="properties">
<syntaxhighlight lang="properties">
Name: myCompany/myPackage/
Name: myCompany/myPackage/
Sealed: true
Sealed: true
</syntaxhighlight>
</source>
The Name header's value is the package's relative pathname. Note that it ends with a '/' to distinguish it from a filename. Any headers following a Name header, without any intervening blank lines, apply to the file or package specified in the Name header. In the above example, because the <code>Sealed</code> header occurs after the <code>Name: myCompany/myPackage</code> header with no intervening blank lines, the <code>Sealed</code> header applies (only) to the package <code>myCompany/myPackage</code>.
The Name header's value is the package's relative pathname. Note that it ends with a '/' to distinguish it from a filename. Any headers following a Name header, without any intervening blank lines, apply to the file or package specified in the Name header. In the above example, because the <code>Sealed</code> header occurs after the <code>Name: myCompany/myPackage</code> header with no intervening blank lines, the <code>Sealed</code> header applies (only) to the package <code>myCompany/myPackage</code>.


The feature of sealed packages is outmoded by the Java Platform Module System introduced in Java 9, in which modules cannot split packages.<ref name="JEP 261: Module System">{{cite web | url=https://openjdk.java.net/jeps/261 | title=JEP 261: Module System | access-date=2021-02-06}}</ref>
⚫
===Package Versioning===

⚫
====Package Versioning====
Several manifest headers hold versioning information. One set of headers can be assigned to each package. The versioning headers appear directly beneath the Name header for the package. This example shows all the versioning headers:
Several manifest headers hold versioning information. One set of headers can be assigned to each package. The versioning headers appear directly beneath the Name header for the package. This example shows all the versioning headers:
<source lang="properties">
<syntaxhighlight lang="properties">
Name: java/util/
Name: java/util/
Specification-Title: "Java Utility Classes"
Specification-Title: "Java Utility Classes"
Line 88: Line 93:
Implementation-Version: "build57"
Implementation-Version: "build57"
Implementation-Vendor: "Sun Microsystems, Inc."
Implementation-Vendor: "Sun Microsystems, Inc."
</syntaxhighlight>
</source>

====Multi-Release====
A jar can be optionally marked as a multi-release jar. Using the multi-release feature allows library developers to load different code depending on the version of the Java runtime.<ref name="JEP 238: Multi-Release JAR Files">{{cite web | url=https://openjdk.java.net/jeps/238 | title=JEP 238: Multi-Release JAR Files | access-date=2021-02-06}}</ref> This in turn allows developers to leverage new features without sacrificing compatibility.

A multi-release jar is enabled using the following declaration in the manifest:
<syntaxhighlight lang="properties">
Multi-Release: true
</syntaxhighlight>


===Dependencies===
====Dependencies====
The <code>MANIFEST.MF</code> file can be used to specify all the classes that must be loaded for an application to be able to run.<ref>the sun servlet specification, page 72 (servlet-2_4-fr-spec.pdf). See also the [https://docs.oracle.com/javase/8/docs/technotes/tools/findingclasses.html Java Tech Notes].</ref>
The <code>MANIFEST.MF</code> file can be used to specify all the classes that must be loaded for an application to be able to run.<ref>the sun servlet specification, page 72 (servlet-2_4-fr-spec.pdf). See also the [https://docs.oracle.com/javase/8/docs/technotes/tools/findingclasses.html Java Tech Notes].</ref>


Note that Class-Path entries are delimited with spaces, not with the system path delimiter:
Note that Class-Path entries are delimited with spaces, not with the system path delimiter:
<source lang="properties">
<syntaxhighlight lang="properties">
Class-Path: . pkg1.jar path/to/pkg2.jar
Class-Path: . pkg1.jar path/to/pkg2.jar
</syntaxhighlight>
</source>


==Apache Ant Zip/JAR support==
==Apache Ant Zip/JAR support==
The [[Apache Ant]] build tool has its own package to read and write Zip and JAR archives, including support for [[Unix]] [[filesystem]] extensions. The org.apache.tools.zip package is released under the [[Apache Software Foundation OpenOffice|Apache Software Foundation]] license and is designed to be usable outside Ant.
The [[Apache Ant]] build tool has its own package to read and write Zip and JAR archives, including support for [[Unix]] [[filesystem]] extensions. The org.apache.tools.zip package is released under the [[Apache Software Foundation OpenOffice|Apache Software Foundation]] license and is designed to be usable outside Ant.


== Related formats ==
==Related formats==
Several related file formats build on the JAR format:
Several related file formats build on the JAR format:
* [[WAR (Sun file format)|WAR]] (Web application archive) files, also Java archives, store [[XML]] files, Java classes, [[JavaServer Pages]] and other objects for Web Applications.
* [[WAR (Sun file format)|WAR]] (Web application archive) files, also Java archives, store [[XML]] files, Java classes, [[JavaServer Pages]] and other objects for Web Applications.
* [[Resource Adapter|RAR]] (resource adapter archive) files (not to be confused with the [[RAR file format]]), also Java archives, store XML files, Java classes and other objects for [[J2EE Connector Architecture]] (JCA) applications.
* [[Resource Adapter|RAR]] (resource adapter archive) files (not to be confused with the [[RAR file format]]), also Java archives, store XML files, Java classes and other objects for [[J2EE Connector Architecture]] (JCA) applications.
* [[EAR (file format)|EAR]] (enterprise archive) files provide composite Java archives that combine XML files, Java classes and other objects including JAR, WAR and RAR Java archive files for Enterprise Applications.
* [[EAR (file format)|EAR]] (enterprise archive) files provide composite Java archives that combine XML files, Java classes and other objects including JAR, WAR and RAR Java archive files for Enterprise Applications.
* [[Service Archive|SAR]] (service archive) is similar to EAR. It provides a <tt>service.xml</tt> file and accompanying JAR files.
* [[Service Archive|SAR]] (service archive) is similar to EAR. It provides a <code>service.xml</code> file and accompanying JAR files.
* [[APK (file format)|APK]] (Android Application Package), a variant of the Java archive format, is used for [[Android (operating system)|Android]] applications.<ref>{{cite web|url=https://developer.android.com/guide/appendix/glossary.html|title=Glossary|website=developer.android.com}}</ref>
* [[APK (file format)|APK]] (Android application package), a variant of the Java archive format, is used for [[Android (operating system)|Android]] applications.<ref>{{cite web|url=https://developer.android.com/guide/appendix/glossary.html|title=Glossary|website=developer.android.com}}</ref>
* [[AAR (file format)|AAR]] (Android ) is used for distribution of [[Android (operating system)|Android]] libraries, typically via [[Apache Maven|Maven]].<ref>{{cite web|url=https://developer.android.com/studio/projects/android-library.html#aar-contents|title=Android library|website=developer.android.com}}</ref>
* [[AAR (file format)|AAR]] (Android archive) is used for distribution of [[Android (operating system)|Android]] libraries, typically via [[Apache Maven|Maven]].<ref>{{cite web|url=https://developer.android.com/studio/projects/android-library.html#aar-contents|title=Android library|website=developer.android.com}}</ref>
* PAR (Plan ARchive) - supported by [[Virgo (software)|Eclipse Virgo]] [[OSGi]] application server, allows the deployment of multi-bundle OSGi applications as a single archive and provides isolation from other PAR-based applications deployed in the same server.
* PAR (plan archive) – supported by [[Virgo (software)|Eclipse Virgo]] [[OSGi]] application server, allows the deployment of multi-bundle OSGi applications as a single archive and provides isolation from other PAR-based applications deployed in the same server.
* KAR (Karaf ARchive) - supported by [[Apache Karaf]] OSGi application server, allows the deployment of multi-bundle, multi-feature OSGi applications.
* KAR (Karaf archive) – supported by [[Apache Karaf]] OSGi application server, allows the deployment of multi-bundle, multi-feature OSGi applications.


==See also==
==See also==
{{Portal|Computer programming}}
{{Portal|Computer programming}}
* [[Java Classloader#JAR hell|JAR hell]]
* [[Java class loader#JAR hell|JAR hell]]
* [[Java Module System]]
* [[Java Platform Module System]]
* [[Open Packaging Conventions]]
* [[Open Packaging Conventions]]
* [[JAD (file format)]]
* [[JAD (file format)]]
* [[Polyglot (computing)#GIFAR_attack|GIFAR attack]]
* [[Gifar]]
* [[Static library|.a static libraries]]


==References==
==References==
{{Reflist}}
{{Reflist}}


== External links ==
==External links==
* [http://download.oracle.com/javase/6/docs/technotes/guides/jar/jarGuide.html JAR File Overview]
* [https://docs.oracle.com/en/java/javase/20/docs/specs/jar/jar.html JAR File Specification]
* [http://download.oracle.com/javase/6/docs/technotes/guides/jar/jar.html JAR File Specification]
* [https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jarGuide.html JAR File Overview]
* [http://www.cse.yorku.ca/tech/other/jdk1.2.1/docs/guide/jar/manifest.html Original JAR File Specification]


{{Archive formats}}
{{Archive formats}}

Latest revision as of 02:52, 24 November 2024

Java Archive
KDE JAR file icon
KDE JAR file icon
Filename extension
.jar
Internet media type
application/java-archive[1][2][3]
Uniform Type Identifier (UTI)com.sun.java-archive
Magic number50 4b 03 04 ASCII:PK\x03\x04
Developed byNetscape, Sun Microsystems, Oracle Corporation
Type of formatFile archive, data compression
Extended fromZIP

A JAR ("Java archive") file is a package file format typically used to aggregate many Java class files and associated metadata and resources (text, images, etc.) into one file for distribution.[4]

JAR files are archive files that include a Java-specific manifest file. They are built on the ZIP format and typically have a .jar file extension.[5]

Design

[edit]

A JAR file allows Java runtimes to efficiently deploy an entire application, including its classes and their associated resources, in a single request. JAR file elements may be compressed, shortening download times.

A JAR file may contain a manifest file, that is located at META-INF/MANIFEST.MF. The entries in the manifest file describe how to use the JAR file. For instance, a Classpath entry can be used to specify other JAR files to load with the JAR.

Extraction

[edit]

The contents of a file may be extracted using any archive extraction software that supports the ZIP format, or the jar command line utility provided by the Java Development Kit.

Security

[edit]

Developers can digitally sign JAR files. In that case, the signature information becomes part of the embedded manifest file. The JAR itself is not signed, but instead every file inside the archive is listed along with its checksum; it is these checksums that are signed. Multiple entities may sign the JAR file, changing the JAR file itself with each signing, although the signed files themselves remain valid. When the Java runtime loads signed JAR files, it can validate the signatures and refuse to load classes that do not match the signature. It can also support 'sealed' packages, in which the Classloader will only permit Java classes to be loaded into the same package if they are all signed by the same entities. This prevents malicious code from being inserted into an existing package, and so gaining access to package-scoped classes and data.

The content of JAR files may be obfuscated to make reverse engineering more difficult.

Executable JAR files

[edit]

An executable Java program can be packaged in a JAR file, along with any libraries the program uses. Executable JAR files have the manifest specifying the entry point class with Main-Class: myPrograms.MyClass and an explicit Class-Path (and the -cp argument is ignored). Some operating systems can run these directly when clicked. The typical invocation is java -jar foo.jar from a command line.

Native launchers can be created on most platforms. For instance, Microsoft Windows users who prefer having Windows EXE files can use tools such as JSmooth, Launch4J, WinRun4J or Nullsoft Scriptable Install System to wrap single JAR files into executables.

Manifest

[edit]

A manifest file is a metadata file contained within a JAR.[6][7] It defines extension and package-related data. It contains name–value pairs organized in sections. If a JAR file is intended to be used as an executable file, the manifest file specifies the main class of the application. The manifest file is named MANIFEST.MF. The manifest directory has to be the first entry of the compressed archive.

Specifications

[edit]

The manifest appears at the canonical location META-INF/MANIFEST.MF.[8] There can be only one manifest file in an archive and it must be at that location.

The content of the manifest file in a JAR file created with version 1.0 of the Java Development Kit is the following. 

Manifest-Version: 1.0

The name is separated from its value by a colon. The default manifest shows that it conforms to version 1.0 of the manifest specification.

The manifest can contain information about the other files that are packaged in the archive. Manifest contents depend on the intended use for the JAR file. The default manifest file makes no assumptions about what information it should record about other files, so its single line contains data only about itself. It should be encoded in UTF-8.

Special-Purpose Manifest Headers

[edit]

JAR files created only for the purpose of archiving do not use the MANIFEST.MF file.

Most uses of JAR files go beyond simple archiving and compression and require special information in the manifest file.

Features

[edit]

The manifest allows developers to define several useful features for their jars. Properties are specified in key-value pairs.

Applications

[edit]

If an application is contained in a JAR file, the Java Virtual Machine needs to know the application's entry point. An entry point is any class with a public static void main(String[] args) method. This information is provided in the manifest Main-Class header, which has the general form: 

Main-Class: com.example.MyClassName

In this example com.example.MyClassName.main() executes at application launch.

Package Sealing

[edit]

Optionally, a package within a JAR file can be sealed, which means that all classes defined in that package are archived in the same JAR file. A package might be sealed to ensure version consistency among the classes in the software or as a security measure.

To seal a package, a Name entry needs to appear, followed by a Sealed header, such as: 

Name: myCompany/myPackage/
Sealed: true

The Name header's value is the package's relative pathname. Note that it ends with a '/' to distinguish it from a filename. Any headers following a Name header, without any intervening blank lines, apply to the file or package specified in the Name header. In the above example, because the Sealed header occurs after the Name: myCompany/myPackage header with no intervening blank lines, the Sealed header applies (only) to the package myCompany/myPackage.

The feature of sealed packages is outmoded by the Java Platform Module System introduced in Java 9, in which modules cannot split packages.[9]

Package Versioning

[edit]

Several manifest headers hold versioning information. One set of headers can be assigned to each package. The versioning headers appear directly beneath the Name header for the package. This example shows all the versioning headers: 

Name: java/util/
Specification-Title: "Java Utility Classes"
Specification-Version: "1.2"
Specification-Vendor: "Sun Microsystems, Inc.".
Implementation-Title: "java.util"
Implementation-Version: "build57"
Implementation-Vendor: "Sun Microsystems, Inc."

Multi-Release

[edit]

A jar can be optionally marked as a multi-release jar. Using the multi-release feature allows library developers to load different code depending on the version of the Java runtime.[10] This in turn allows developers to leverage new features without sacrificing compatibility.

A multi-release jar is enabled using the following declaration in the manifest: 

Multi-Release: true

Dependencies

[edit]

The MANIFEST.MF file can be used to specify all the classes that must be loaded for an application to be able to run.[11]

Note that Class-Path entries are delimited with spaces, not with the system path delimiter: 

Class-Path: . pkg1.jar path/to/pkg2.jar

Apache Ant Zip/JAR support

[edit]

The Apache Ant build tool has its own package to read and write Zip and JAR archives, including support for Unix filesystem extensions. The org.apache.tools.zip package is released under the Apache Software Foundation license and is designed to be usable outside Ant.

[edit]

Several related file formats build on the JAR format:

  • WAR (Web application archive) files, also Java archives, store XML files, Java classes, JavaServer Pages and other objects for Web Applications.
  • RAR (resource adapter archive) files (not to be confused with the RAR file format), also Java archives, store XML files, Java classes and other objects for J2EE Connector Architecture (JCA) applications.
  • EAR (enterprise archive) files provide composite Java archives that combine XML files, Java classes and other objects including JAR, WAR and RAR Java archive files for Enterprise Applications.
  • SAR (service archive) is similar to EAR. It provides a service.xml file and accompanying JAR files.
  • APK (Android application package), a variant of the Java archive format, is used for Android applications.[12]
  • AAR (Android archive) is used for distribution of Android libraries, typically via Maven.[13]
  • PAR (plan archive) – supported by Eclipse Virgo OSGi application server, allows the deployment of multi-bundle OSGi applications as a single archive and provides isolation from other PAR-based applications deployed in the same server.
  • KAR (Karaf archive) – supported by Apache Karaf OSGi application server, allows the deployment of multi-bundle, multi-feature OSGi applications.

See also

[edit]

References

[edit]
  1. ^ "File Extension .JAR Details". Retrieved 29 November 2012.
  2. ^ "MIME : Java Glossary". Retrieved 29 November 2012.
  3. ^ "IANA Assignment". Retrieved 12 May 2023.
  4. ^ "JDK 6 Java Archive (JAR)-related APIs & DeveloperGuides".
  5. ^ "JAR File Specification". Java SE Documentation. Oracle. Archived from the original on 2017-09-11.
  6. ^ "Understanding the Manifest". Java.sun.com. 2003-03-21. Retrieved 2012-07-31.
  7. ^ "JAR File Specification". Download.oracle.com. Retrieved 2012-07-31.
  8. ^ "JAR File Specification". Download.oracle.com. Retrieved 2012-07-31.
  9. ^ "JEP 261: Module System". Retrieved 2021-02-06.
  10. ^ "JEP 238: Multi-Release JAR Files". Retrieved 2021-02-06.
  11. ^ the sun servlet specification, page 72 (servlet-2_4-fr-spec.pdf). See also the Java Tech Notes.
  12. ^ "Glossary". developer.android.com.
  13. ^ "Android library". developer.android.com.
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