use strict;
use Archive::Zip;

#read the .jar file
my $zip = Archive::Zip->new( 'helloworld.jar' );

# extract what you want
my $file = "content/helloworld/helloworldOverlay.js";
my $member = $zip->extractMember($file);

# do something with the file $file

# now add it back
$zip->removeMember($member);
$zip->addFile($file);
$zip->overwrite();