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<title>Jar Task</title>
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<body>

<h2 id="jar">Jar</h2>
<h3>Description</h3>
<p>Jars a set of files.</p>
<p>The <var>basedir</var> attribute is the reference directory from where to jar.</p>
<p>Note that file permissions will not be stored in the resulting jarfile.</p>

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

<p>This task forms an implicit <a href="../Types/fileset.html">FileSet</a> and supports most
attributes of <code>&lt;fileset&gt;</code> (<var>dir</var> becomes <var>basedir</var>) as well as
the nested <code>&lt;include&gt;</code>, <code>&lt;exclude&gt;</code>
and <code>&lt;patternset&gt;</code> elements.</p>
<p>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 <code>fileset</code>
and <code>groupfileset</code> child elements from the <code>zip</code> task are also available in
the <code>jar</code> task.  See the <a href="zip.html">Zip</a> task for more details and
examples.</p>

<p>The <var>update</var> parameter controls what happens if the JAR file already exists. When set
to <q>yes</q>, the JAR file is updated with the files specified. When set to <q>no</q> (the default)
the JAR file is overwritten. An example use of this is provided in the <a href="zip.html">Zip task
documentation</a>.  Please note that ZIP files store file modification times with a granularity of 2
seconds.  If a file is less than 2 seconds newer than the entry in the archive, Ant will not
consider it newer.</p>

<p>If the manifest is omitted, a simple one will be supplied by Apache Ant.</p>

<p>The <var>whenmanifestonly</var> parameter controls what happens when no files, apart from the
manifest file, or nested services, match.  If <q>skip</q>, the JAR is not created and a warning is
issued.  If <q>fail</q>, the JAR is not created and the build is halted with an error.
If <q>create</q> (default), an empty JAR file (only containing a manifest and services) is
created.</p>

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

<p>Manifests are processed by the <code>Jar</code> task according to
the <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html" target="_top">Jar
file specification.</a>  Note in particular that this may result in manifest lines greater than 72
bytes being wrapped and continued on the next line.</p>

<p>The <code>Jar</code> task checks whether you specified package information according to
the <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/versioning/spec/versioning2.html#wp90779"
target="_top">versioning specification</a>.</p>

<p><strong>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 <var>duplicate</var> attribute to a value
other than its default, <q>add</q>.</strong></p>

<p>To cryptographically sign your JAR file, use the <a href="signjar.html">SignJar task</a> on the
JAR that you create from this task.</p>

<p>For creating a simple version of a <a href="https://openjdk.java.net/jeps/238" target="_top">JEP
238 multi-release jar</a>, you don't need any special tools. Just set the
required <code>manifest</code> entry and place the files where required, as you could see in
the <a href="#jep238-example">JEP 238 example</a>. If you want to tune this kind of jar,
e.g. decreasing the size by deleting 'same' classes from the versions-branches, you have to do more
...</p>

<h3>Parameters</h3>
<table class="attr">
  <tr>
    <th scope="col">Attribute</th>
    <th scope="col">Description</th>
    <th scope="col">Required</th>
  </tr>
  <tr>
    <td>destfile</td>
    <td>the JAR file to create.</td>
    <td>Yes</td>
  </tr>
  <tr>
    <td>basedir</td>
    <td>the directory from which to jar the files.</td>
    <td>No</td>
  </tr>
  <tr>
    <td>compress</td>
    <td>Not only store data but also compress them.  Unless you set the <var>keepcompression</var>
      attribute to <q>false</q>, this will apply to the entire archive, not only the files you've
      added while updating.</td>
    <td>No; defaults to <q>true</q></td>
  </tr>
  <tr>
    <td>keepcompression</td>
    <td>For entries coming from existing archives (like nested <code>zipfileset</code>s or while
      updating the archive), keep the compression as it has been originally instead of using the
    <var>compress</var> attribute.  <em>Since Ant 1.6</em></td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>encoding</td>
    <td>The character encoding to use for filenames inside the archive. <strong>It is not
      recommended to change this value as the created archive will most likely be unreadable for
      Java otherwise.</strong>  <br/>See also the <a href="zip.html#encoding">discussion in the zip
      task page</a></td>
    <td>No; defaults to <q>UTF8</q></td>
  </tr>
  <tr>
    <td>filesonly</td>
    <td>Store only file entries</td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>includes</td>
    <td>comma- or space-separated list of patterns of files that must be included</td>
    <td>No; defaults to all (<q>**</q>)</td>
  </tr>
  <tr>
    <td>includesfile</td>
    <td>name of a file. Each line of this file is taken to be an include pattern</td>
    <td>No</td>
  </tr>
  <tr>
    <td>excludes</td>
    <td>comma- or space-separated list of patterns of files that must be excluded</td>
    <td>No; defaults to default excludes or none if <var>defaultexcludes</var> is <q>no</q></td>
  </tr>
  <tr>
    <td>excludesfile</td>
    <td>Name of a file. Each line of this file is taken to be an exclude pattern</td>
    <td>No</td>
  </tr>
  <tr>
    <td>defaultexcludes</td>
    <td>indicates whether default excludes should be used or not (<q>yes|no</q>)</td>
    <td>No; defaults to <q>yes</q></td>
  </tr>
  <tr>
    <td>manifest</td>
    <td>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 <samp>META-INF/MANIFEST.MF</samp></td>
    <td>No</td>
  </tr>
  <tr>
    <td>filesetmanifest</td>
    <td>behavior when a manifest is found in a <code>zipfileset</code>
      or <code>zipgroupfileset</code> file.  Valid values are <q>skip</q>, <q>merge</q>,
      and <q>mergewithoutmain</q>.  <q>merge</q> will merge all of the manifests together, and merge
      this into any other specified manifests.  <q>mergewithoutmain</q> merges everything but the
      Main section of the manifests.
    </td>
    <td>No; defaults to <q>skip</q></td>
  </tr>
  <tr>
    <td>update</td>
    <td>indicates whether to update or overwrite the destination file if it already exists</td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>whenmanifestonly</td>
    <td>behavior when no files match.  Valid values are <q>fail</q>, <q>skip</q>,
      and <q>create</q>.</td>
    <td>No; defaults to <q>create</q></td>
  </tr>
  <tr>
    <td>duplicate</td>
    <td>behavior when a duplicate file is found.  Valid values are <q>add</q>, <q>preserve</q>,
      and <q>fail</q>.</td>
    <td>No; defaults to <q>add</q></td>
  </tr>
  <tr>
    <td>index</td>
    <td>whether to create
      an <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html#JAR_Index"
      target="_top">index list</a> to speed up classloading.
      Unless you specify additional jars with nested <a href="#indexjars"><code>indexjars</code></a>
      elements, only the contents of this jar will be included in the index.</td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>indexMetaInf</td>
    <td>whether to include <samp>META-INF</samp> and its children in the index.  Doesn't have any
      effect if <var>index</var> is <q>false</q>.<br/>Sun's jar implementation used to skip
      the <samp>META-INF</samp> directory and Ant followed that example.  The behavior has been
      changed with <a href="https://bugs.openjdk.java.net/browse/JDK-4408526" target="_top">Java
      5</a>.  In order to avoid problems with Ant generated jars on Java 1.4 or earlier Ant will not
      include <samp>META-INF</samp> unless explicitly asked to. <em>Since Ant 1.8.0</em></td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>manifestencoding</td>
    <td>The encoding used to read the JAR manifest, when a manifest file is specified.  The task
      will always use UTF-8 when writing the manifest.</td>
    <td>No; defaults to default JVM character encoding</td>
  </tr>
  <tr>
    <td>roundup</td>
    <td>Whether the file modification times will be rounded up to the next even number of
      seconds.<br/>Zip archives store file modification times with a granularity of 2 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. <em>Since Ant 1.6.2</em></td>
    <td>No; defaults to <q>true</q></td>
  </tr>
  <tr>
    <td>level</td>
    <td>Non-default level at which file compression should be performed. Valid values range
      from <q>0</q> (no compression/fastest) to <q>9</q> (maximum compression/slowest). <em>Since
      Ant 1.7</em></td>
    <td>No</td>
  </tr>
  <tr>
    <td>strict</td>
    <td>Configures how to handle breaks of the packaging version specification:
      <ul>
        <li><q>fail</q> = throws a BuildException</li>
        <li><q>warn</q> = logs a message on warn level</li>
        <li><q>ignore</q> = logs a message on verbose level (default)</li>
      </ul><em>Since Ant 1.7.1</em></td>
    <td>No; defaults to <q>ignore</q></td>
  </tr>
  <tr>
    <td>preserve0permissions</td>
    <td>when updating an archive or adding entries from a different archive Ant will assume that a
      Unix permissions value of 0 (nobody is allowed to do anything to the file/directory) means
      that the permissions haven't been stored at all rather than real permissions and will instead
      apply its own default values.<br/>  Set this attribute to <q>true</q> if you really want to
      preserve the original permission field. <em>since Ant 1.8.0</em>
    </td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>useLanguageEncodingFlag</td>
    <td>Whether to set the language encoding flag if the encoding is UTF-8.  This setting doesn't
      have any effect if the encoding is not UTF-8. <em>Since Ant 1.8.0</em>.  <br/>See also
      the <a href="zip.html#encoding">discussion in the zip task page</a></td>
    <td>No; defaults to <q>true</q></td>
  </tr>
  <tr>
    <td>createUnicodeExtraFields</td>
    <td>Whether to create Unicode extra fields to store the file names a second time inside the
      entry's metadata.<br/>Possible values are <q>never</q>, <q>always</q>
      and <q>not-encodeable</q> which will only add Unicode extra fields if the file name
      cannot.<br/>See also the <a href="zip.html#encoding">discussion in the zip task page</a></td>
    <td>No; defaults to <q>never</q></td>
  </tr>
  <tr>
    <td>fallbacktoUTF8</td>
    <td>Whether to use UTF-8 and the language encoding flag instead of the specified encoding if a
      file name cannot be encoded using the specified encoding. <em>Since Ant 1.8.0</em>.<br/>See
      also the <a href="zip.html#encoding">discussion in the zip task page</a></td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>mergeClassPathAttributes</td>
    <td>Whether to merge the <code>Class-Path</code> attributes found in different manifests (if
      merging manifests).  If <q>false</q>, only the attribute of the last merged manifest will be
      preserved.  <em>Since Ant 1.8.0</em>.<br/>Unless you also set <var>flattenAttributes</var>
      to <q>true</q>, this may result in manifests containing multiple <code>Class-Path</code>
      attributes which violates the manifest specification.</td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>flattenAttributes</td>
    <td>Whether to merge attributes occurring more than once in a section (this can only happen for
      the <code>Class-Path</code> attribute) into a single attribute.  <em>Since Ant
      1.8.0</em>.</td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>zip64Mode</td>
    <td>When to use Zip64 extensions for entries.  The possible values
      are <q>never</q>, <q>always</q> and <q>as-needed</q>.  <em>Since Ant 1.9.1</em>.<br/>See also
      the <a href="zip.html#zip64">discussion in the zip task page</a></td>
    <td>No; defaults to <q>never</q></td>
  </tr>
  <tr>
    <td valign="top">modificationtime</td>
    <td valign="top">Set all stored file modification times to the
    given time. This can either be a number interpreted as
    milliseconds since 1970-01-01T00:00:00Z or a string that can be
    parsed as a ISO 8601 timestamp with optional timezone.
      <em>Since Ant 1.10.2</em>.
    </td>
    <td align="center" valign="top">No</td>
  </tr>
</table>

<h3>Parameters specified as nested elements</h3>
<h4>metainf</h4>
<p>The nested <code>metainf</code> element specifies
a <a href="../Types/fileset.html">FileSet</a>. All files included in this fileset will end up in
the <samp>META-INF</samp> directory of the jar file. If this fileset includes a file
named <samp>MANIFEST.MF</samp>, the file is ignored and you will get a warning.</p>

<h4>manifest</h4>
<p>The nested <code>manifest</code> 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
<a href="manifest.html">manifest</a> task, but the <var>file</var> and <var>mode</var>
attributes must be omitted.</p>
<p>If both an inline manifest and an external file are both specified, the manifests are merged.</p>

<p>When using inline manifests, the <code>Jar</code> 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.</p>

<h4 id="indexjars">indexjars</h4>

<p><em>Since Ant 1.6.2</em></p>

<p>The nested <code>indexjars</code> element specifies a <a href="../using.html#path">path-like
structure</a>.  Its content is completely ignored unless you set the <var>index</var> attribute of
the task to <q>true</q>.</p>

<p>The index created by this task will contain indices for the archives contained in this path, the
names used for the archives depend on your manifest:</p>
<ul>
  <li>If the generated jar's manifest contains no <code>Class-Path</code> attribute, the file name
  without any leading directory path will be used and all parts of the path will get indexed.</li>
  <li>If the manifest contains a <code>Class-Path</code> attribute, this task will try to guess
  which part of the <code>Class-Path</code> belongs to a given archive.  If it cannot guess a name,
  the archive will be skipped, otherwise the name listed inside the <code>Class-Path</code>
  attribute will be used.</li>
</ul>

<p>This task will not create any index entries for archives that are empty or only contain files
inside the <samp>META-INF</samp> directory unless the <var>indexmetainf</var> attribute has been set
to <q>true</q>.</p>

<h4 id="indexjarsmapper">indexjarsmapper</h4>

<p><em>Since Ant 1.10.9</em></p>

<p>The nested <code>indexjarsmapper</code> element can be used to perform custom filename
transformations for the archives specified by <code>indexjars</code> if the
<a href="#indexjars">default filename transformation</a> doesn't suffice.

<h4 id="service">service</h4>

<p><em>Since Ant 1.7.0</em></p>

<p>The nested <code>service</code> element specifies a service.  Services are described in
the <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html#Service_Provider"
target="_top">service provider overview</a>.  The approach is to have providers JARs include files
named by the service provided, for
example, <samp>META-INF/services/javax.script.ScriptEngineFactory</samp> which can include
implementation class names, one per line (usually just one per JAR).</p>

<p>The name of the service is set by the <var>type</var> attribute. The classname implementing the
service is the the <var>provider</var> attribute, or if one wants to specify a number of classes
that implement the service, by <code>provider</code> nested elements.</p>
<table class="attr">
  <tr>
    <th scope="col">Attribute</th>
    <th scope="col">Description</th>
    <th scope="col">Required</th>
  </tr>
  <tr>
    <td>type</td>
    <td>The name of the service.</td>
    <td>Yes</td>
  </tr>
  <tr>
    <td>provider</td>
    <td>The classname of the class implementing the service.</td>
    <td>Yes, unless there is a nested <code>&lt;provider&gt;</code> element.</td>
  </tr>
</table>
<p>The provider classname is specified either by the <var>provider</var> attribute, or by a
nested <code>&lt;provider&gt;</code> element, which has a single <var>classname</var> attribute.  If
a JAR file has more that one implementation of the service, a number of
nested <code>&lt;provider&gt;</code> elements may be used.</p>

<h3>Examples</h3>

<h4>Simple</h4>
<p>Jar all files in the <samp>${build}/classes</samp> directory into a file
called <samp>app.jar</samp> in the <samp>${dist}/lib</samp> directory.</p>
<pre>&lt;jar destfile=&quot;${dist}/lib/app.jar&quot; basedir=&quot;${build}/classes&quot;/&gt;</pre>

<h4>With filters</h4>

<p>Jar all files in the <samp>${build}/classes</samp> directory into a file
called <samp>app.jar</samp> in the <samp>${dist}/lib</samp> directory. Files with the
name <samp>Test.class</samp> are excluded.</p>
<pre>&lt;jar destfile=&quot;${dist}/lib/app.jar&quot;
     basedir=&quot;${build}/classes&quot;
     excludes=&quot;**/Test.class&quot;/&gt;</pre>

<p>Jar all files in the <samp>${build}/classes</samp> directory into a file
called <samp>app.jar</samp> in the <samp>${dist}/lib</samp> directory. Only files under the
directory <samp>mypackage/test</samp> are used, and files with the name <samp>Test.class</samp> are
excluded.</p>
<pre>
&lt;jar destfile=&quot;${dist}/lib/app.jar&quot;
     basedir=&quot;${build}/classes&quot;
     includes=&quot;mypackage/test/**&quot;
     excludes=&quot;**/Test.class&quot;/&gt;</pre>

<h4>Multiple filesets</h4>
<p>Jar all files in the <samp>${build}/classes</samp> directory and also in
the <samp>${src}/resources</samp> directory together into a file called <samp>app.jar</samp> in
the <samp>${dist}/lib</samp> directory. Files with the name <samp>Test.class</samp> are excluded. If
there are files such as <samp>${build}/classes/mypackage/MyClass.class</samp>
and <samp>${src}/resources/mypackage/image.gif</samp>, they will appear in the same directory in the
jar (and thus be considered in the same package by Java).</p>
<pre>
&lt;jar destfile=&quot;${dist}/lib/app.jar&quot;&gt;
    &lt;fileset dir=&quot;${build}/classes&quot;
             excludes=&quot;**/Test.class&quot;/&gt;
    &lt;fileset dir=&quot;${src}/resources&quot;/&gt;
&lt;/jar&gt;</pre>

<h4>Merging archives</h4>

<p>Create an executable jar file with a main class <samp>com.acme.checksites.Main</samp>, and embed
all the classes from the jar <samp>lib/main/some.jar</samp>.</p>
<pre>
&lt;jar destfile="build/main/checksites.jar"&gt;
    &lt;fileset dir="build/main/classes"/&gt;
    &lt;zipfileset includes="**/*.class" src="lib/main/some.jar"/&gt;
    &lt;manifest&gt;
      &lt;attribute name="Main-Class"
                 value="com.acme.checksites.Main"/&gt;
    &lt;/manifest&gt;
&lt;/jar&gt;</pre>

<p>Create an executable jar file with a main class <samp>com.acme.checksites.Main</samp>, and embed
all the classes from all the jars in <samp>lib/main</samp>.</p>
<pre>
&lt;jar destfile="build/main/checksites.jar"&gt;
    &lt;fileset dir="build/main/classes"/&gt;
    &lt;restrict&gt;
       &lt;name name="**/*.class"/&gt;
       &lt;archives&gt;
           &lt;zips&gt;
               &lt;fileset dir="lib/main" includes="**/*.jar"/&gt;
           &lt;/zips&gt;
       &lt;/archives&gt;
    &lt;/restrict&gt;
    &lt;manifest&gt;
        &lt;attribute name="Main-Class"
              value="com.acme.checksites.Main"/&gt;
    &lt;/manifest&gt;
&lt;/jar&gt;</pre>

<h4>Inline manifest</h4>
<pre>
&lt;jar destfile=&quot;test.jar&quot; basedir=&quot;.&quot;&gt;
    &lt;include name=&quot;build&quot;/&gt;
    &lt;manifest&gt;
        &lt;!-- If this is an Applet or Web Start application, include
             the proper attributes from <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/jweb/index.html" target="_top">https://docs.oracle.com/javase/8/docs/technotes/guides/jweb/index.html</a> --&gt;
        &lt;attribute name=&quot;Permissions&quot; value=&quot;sandbox&quot;/&gt;
        &lt;attribute name=&quot;Codebase&quot; value=&quot;example.com&quot;/&gt;
        &lt;!-- Who is building this jar? --&gt;
        &lt;attribute name=&quot;Built-By&quot; value=&quot;${user.name}&quot;/&gt;
        &lt;!-- Information about the program itself --&gt;
        &lt;attribute name=&quot;Implementation-Vendor&quot; value=&quot;ACME inc.&quot;/&gt;
        &lt;attribute name=&quot;Implementation-Title&quot; value=&quot;GreatProduct&quot;/&gt;
        &lt;attribute name=&quot;Implementation-Version&quot; value=&quot;1.0.0beta2&quot;/&gt;
        &lt;!-- details --&gt;
        &lt;section name=&quot;common/MyClass.class&quot;&gt;
            &lt;attribute name=&quot;Sealed&quot; value=&quot;false&quot;/&gt;
        &lt;/section&gt;
    &lt;/manifest&gt;
&lt;/jar&gt;</pre>
<p>This is an example of an inline manifest specification including the version of the build program
(<code>Implementation-Version</code>). Note that the <code>Built-By</code> attribute will take the
value of the Ant property <code>user.name</code>. The manifest produced by the above would look like
this:</p>

<pre>
Manifest-Version: 1.0
Permissions: sandbox
Codebase: example.com
Built-By: conor
Implementation-Vendor: ACME inc.
Implementation-Title: GreatProduct
Implementation-Version: 1.0.0beta2
Created-By: Apache Ant 1.9.2

Name: common/MyClass.class
Sealed: false</pre>

<h4>Service Provider</h4>

<p>The following shows how to create a jar file specifying a service with an implementation of the
scripting interface:</p>
<pre>
&lt;jar destfile="pinky.jar"&gt;
    &lt;fileset dir="build/classes"/&gt;
    &lt;service type="javax.script.ScriptEngineFactory"
             provider="org.acme.PinkyLanguage"/&gt;
&lt;/jar&gt;</pre>

<p>The following shows how to create a jar file specifying a service with two implementations of the
scripting interface:</p>
<pre>
&lt;jar destfile="pinkyandbrain.jar"&gt;
    &lt;fileset dir="classes"/&gt;
    &lt;service type="javax.script.ScriptEngineFactory"&gt;
        &lt;provider classname="org.acme.PinkyLanguage"/&gt;
        &lt;provider classname="org.acme.BrainLanguage"/&gt;
    &lt;/service&gt;
&lt;/jar&gt;</pre>

<h4 id="jep238-example">JEP 238 example: a Multi-Release JAR Files</h4>
<p>Here we want to create a <em>Multi-Release JAR File</em> according the
specification <a href="https://openjdk.java.net/jeps/238" target="_top">JEP 238</a>. It defines on
top of a JAR the possibility to place additional or overwriting classes in a jar, which are
available according to the Java version you run.<br/>Basically it says, that you have to set the
manifest entry <code>Multi-Release: true</code> and place all additional or overwriting classes
in <samp>META-INF/versions/<i>number</i>/package-structure</samp>,
e.g. <samp>META-INF/versions/9/org/apache/ant/MyClass.class</samp></p>
<p>In this example we expect that the normal classes are compiled into <samp>${java.classes}</samp>
and the Java 9 classes are compiled into <samp>${java9.classes}</samp>.</p>
<pre>
&lt;jar destfile=&quot;mrjar.jar&quot;&gt;
    &lt;manifest&gt;
        &lt;!-- special mf-entry according to the spec --&gt;
        &lt;attribute name=&quot;Multi-Release&quot; value=&quot;true&quot;/&gt;
    &lt;/manifest&gt;
    &lt;!-- directory structure according to the spec ... --&gt;
    &lt;!-- ... default classes loadable by old (&lt;Java 9) versions --&gt;
    &lt;fileset dir=&quot;${java.classes}&quot;/&gt;
    &lt;!-- ... per release classes, require Java 9+ for loadable via standard ClassLoader --&gt;
    &lt;zipfileset prefix=&quot;META-INF/versions/9/&quot; dir=&quot;${java9.classes}&quot;/&gt;
&lt;/jar&gt;</pre>

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