Jars a set of files.

The basedir attribute is the reference directory from where to jar.

Note that file permissions will not be stored in the resulting jarfile.

It is possible to refine the set of files that are being jarred. This can be done with the includes, includesfile, excludes, excludesfile and defaultexcludes attributes. With the includes or includesfile attribute you specify the files you want to have included by using patterns. The exclude or excludesfile attribute is used to specify the files you want to have excluded. This is also done with patterns. And finally with the defaultexcludes attribute, you can specify whether you want to use default exclusions or not. See the section on directory based tasks, on how the inclusion/exclusion of files works, and how to write patterns.

This task forms an implicit FileSet and supports all attributes of <fileset> (dir becomes basedir) as well as the nested <include>, <exclude> and <patternset> elements.

You can also use nested file sets for more flexibility, and specify multiple ones to merge together different trees of files into one JAR. The extended fileset and groupfileset child elements from the zip task are also available in the jar task. See the Zip task for more details and examples.

If the manifest is omitted, a simple one will be supplied by Ant.

The update parameter controls what happens if the JAR file already exists. When set to yes, the JAR file is updated with the files specified. When set to no (the default) the JAR file is overwritten. An example use of this is provided in the Zip task documentation. Please note that ZIP files store file modification times with a granularity of two seconds. If a file is less than two seconds newer than the entry in the archive, Ant will not consider it newer.

(The Jar task is a shortcut for specifying the manifest file of a JAR file. The same thing can be accomplished by using the fullpath attribute of a zipfileset in a Zip task. The one difference is that if the manifest attribute is not specified, the Jar task will include an empty one for you.)

Manifests are processed by the Jar task according to the Jar file specification. Note in particular that this may result in manifest lines greater than 72 bytes being wrapped and continued on the next line.

Please note that the zip format allows multiple files of the same fully-qualified name to exist within a single archive. This has been documented as causing various problems for unsuspecting users. If you wish to avoid this behavior you must set the duplicate attribute to a value other than its default, "add".


Attribute Description Required
destfile the JAR file to create. Yes
basedir the directory from which to jar the files. No
compress Not only store data but also compress them, defaults to true. Unless you set the keepcompression attribute to false, this will apply to the entire archive, not only the files you've added while updating. No
keepcompression For entries coming from existing archives (like nested zipfilesets or while updating the archive), keep the compression as it has been originally instead of using the compress attribute. Defaults false. Since Ant 1.6 No
encoding The character encoding to use for filenames inside the archive. Defaults to UTF8. It is not recommended to change this value as the created archive will most likely be unreadable for Java otherwise. No
filesonly Store only file entries, defaults to false No
includes comma- or space-separated list of patterns of files that must be included. All files are included when omitted. No
includesfile the name of a file. Each line of this file is taken to be an include pattern No
excludes comma- or space-separated list of patterns of files that must be excluded. No files (except default excludes) are excluded when omitted. No
excludesfile the name of a file. Each line of this file is taken to be an exclude pattern No
defaultexcludes indicates whether default excludes should be used or not ("yes"/"no"). Default excludes are used when omitted. No
manifest the manifest file to use. This can be either the location of a manifest, or the name of a jar added through a fileset. If its the name of an added jar, the task expects the manifest to be in the jar at META-INF/MANIFEST.MF No
filesetmanifest behavior when a Manifest is found in a zipfileset or zipgroupfileset file is found. Valid values are "skip", "merge", and "mergewithoutmain". "merge" will merge all of the manifests together, and merge this into any other specified manifests. "mergewithoutmain" merges everything but the Main section of the manifests. Default value is "skip". No
update indicates whether to update or overwrite the destination file if it already exists. Default is "false". No
whenempty behavior when no files match. Valid values are "fail", "skip", and "create". Default is "skip". No
duplicate behavior when a duplicate file is found. Valid values are "add", "preserve", and "fail". The default value is "add". No
index whether to create an index list to speed up classloading. This is a JDK 1.3+ specific feature. Unless you specify additional jars with nested indexjars elements, only the contents of this jar will be included in the index. Defaults to false. No
manifestencoding The encoding used to read the JAR manifest, when a manifest file is specified. No, defaults to the platform encoding.
roundup Whether the file modification times will be rounded up to the next even number of seconds.
Zip archives store file modification times with a granularity of two seconds, so the times will either be rounded up or down. If you round down, the archive will always seem out-of-date when you rerun the task, so the default is to round up. Rounding up may lead to a different type of problems like JSPs inside a web archive that seem to be slightly more recent than precompiled pages, rendering precompilation useless.
Defaults to true. Since Ant 1.6.2

Nested elements


The nested metainf element specifies a FileSet. All files included in this fileset will end up in the META-INF directory of the jar file. If this fileset includes a file named MANIFEST.MF, the file is ignored and you will get a warning.


The manifest nested element allows the manifest for the Jar file to be provided inline in the build file rather than in an external file. This element is identical to the manifest task, but the file and mode attributes must be omitted.

If both an inline manifest and an external file are both specified, the manifests are merged.

When using inline manifests, the Jar task will check whether the manifest contents have changed (i.e. the manifest as specified is different in any way from the manifest that exists in the Jar, if it exists. If the manifest values have changed the jar will be updated or rebuilt, as appropriate.


since ant 1.6.2

The nested indexjars element specifies a PATH like structure. Its content is completely ignored unless you set the index attribute of the task to true.

The index created by this task will contain indices for the archives contained in this path, the names used for the archioves depend on your manifest:

  • If the generated jar's manifest contains no Class-Path attribute, the file name without any leading directory path will be used and all parts of the path will get indexed.
  • If the manifest contains a Class-Path attribute, this task will try to guess which part of the Class-Path belongs to a given archive. If it cannot guess a name, the archive will be skipped, otherwise tha name listed inside the Class-PAth attribute will be used.

This task will not create any index entries for archives that are empty or only contain files inside the META-INF directory.


  <jar destfile="${dist}/lib/app.jar" basedir="${build}/classes"/>

jars all files in the ${build}/classes directory into a file called app.jar in the ${dist}/lib directory.

  <jar destfile="${dist}/lib/app.jar"


jars all files in the ${build}/classes directory into a file called app.jar in the ${dist}/lib directory. Files with the name Test.class are excluded.

  <jar destfile="${dist}/lib/app.jar"

jars all files in the ${build}/classes directory into a file called app.jar in the ${dist}/lib directory. Only files under the directory mypackage/test are used, and files with the name Test.class are excluded.

<jar destfile="${dist}/lib/app.jar">
    <fileset dir="${build}/classes"
    <fileset dir="${src}/resources"/>


jars all files in the ${build}/classes directory and also in the ${src}/resources directory together into a file called app.jar in the ${dist}/lib directory. Files with the name Test.class are excluded. If there are files such as ${build}/classes/mypackage/MyClass.class and ${src}/resources/mypackage/image.gif, they will appear in the same directory in the JAR (and thus be considered in the same package by Java).

<jar destfile="test.jar" basedir=".">
    <include name="build"/>
      <attribute name="Built-By" value="${user.name}"/>
      <section name="common/class1.class">
        <attribute name="Sealed" value="false"/>


This is an example of an inline manifest specification. Note that the Built-By attribute will take the value of the Ant property ${user.name}. The manifest produced by the above would look like this:

Manifest-Version: 1.0
Built-By: conor
Created-By: Apache Ant 1.5alpha
Name: common/class1.class
Sealed: false

Source: Apache Ant