How To Re-Jar A Jar File Using Ant

Posted by blogmeister on

October 25, 2013

Well, the truth is, there is no one step way to do this. This is what users tend to do:

Extract the Jar file
Delete the Jar file
Run the Jar command to re-create the Jar file.

So yeah, I can make a batch file for this but since I have no idea how to make one, I decided to use Ant.

Here is my script.

<?xml version="1.0" encoding="UTF-8"?>
<project name="recreate-jar" default="list_jarfiles" basedir=".">
	<taskdef resource="net/sf/antcontrib/antcontrib.properties"/>
	<target name="list_jarfiles" description="list jar files in all subfolders">
		<foreach target="rejar" param="the_file">
    	    <path>
    	        <fileset id="dist.contents" dir="." includes="**/*.jar"/>
    		</path>
    	</foreach>
	</target>
	<target name="rejar" description="unsigns signed jar file">
		<basename property="the_file.filename" file="${the_file}"/>
		<dirname property="absolute.path" file="${the_file}"/>
		<property name="folder_name" value="${absolute.path}_folder"/>
		<!-- 
		delete folder for extracted jar file if exists before proceeding to recreate folder and extract jar contents.
		the folder name should be like JARNAME_folder
		-->
		<if>
            <available file="${folder_name}" type="dir" />
            <then>
                <delete includeemptydirs="true">  
			<fileset dir="${folder_name}" includes="**/**"/>
		</delete>
            </then>
        </if>
		<mkdir dir="${folder_name}" />
		<!-- extract all jar file contents to folder -->
		<unzip src="${the_file}" dest="${folder_name}"/>
		<!-- delete jar file -->
		<delete file="${the_file}" />
		<!-- 
		create jar file using custom manifest. make sure you change the path if ever the folder is different in your workstation.
		-->
		<jar destfile="${the_file}" 
			 duplicate="preserve"
			 manifest="manifest.mf"
			 basedir="${folder_name}"
			 excludes="META-INF/**"
			 includes="**"
		>
		</jar>
		<!-- after creating jar, delete folder of extracted files -->
		<delete includeemptydirs="true">  
			<fileset dir="${folder_name}" includes="**/**"/>
		</delete>
	</target>
</project>

<?xml version="1.0" encoding="UTF-8"?>

<path>

</path>

</foreach>

</target>

<!--

delete folder for extracted jar file if exists before proceeding to recreate folder and extract jar contents.

the folder name should be like JARNAME_folder

-->

<if>

<then>

</delete>

</then>

</if>

<!--

create jar file using custom manifest. make sure you change the path if ever the folder is different in your workstation.

-->

<jar destfile="${the_file}"

duplicate="preserve"

manifest="manifest.mf"

basedir="${folder_name}"

excludes="META-INF/**"

includes="**"

</jar>

</delete>

</target>

</project>

The following explains the steps that the build script executes:

Go over all folders recursively to look for existing jar files.
Extracts them one by one in a folder name that is the name of the Jar file + “_folder”.
Delete the old Jar file
Re-create the Jar file
Delete the folder

That’s it! Simply put the build script file in any folder you want it to start searching for Jar files and it does the rest.