Why aren't all jar files compressed in the JRE installer?

Question

I used 7zip to unpack jre-6u12-windows-i586-p.exe (Oracle JRE Installer). When unpacking, I got core.zip, zipper.exe and several other files.

Again on the explosion of core.zip, I found a few things. core.zip contains all jar files in the same way as after installation, with the exception of 7 jar files.

charsets.jar deploy.jar javaws.jar jsse.jar localedata.jar plugin.jar rt.jar 

Instead of these jar files there are corresponding packfiles

 charsets.pack deploy.pack javaws.pack jsse.pack localedata.pack plugin.pack rt.pack 

I think these are files created by pack200.exe, and unpack200.exe runs on them after installation to create the corresponding jar files.

So now I have a few questions

• Why only these 7 files are launched through the pack200.exe file. I guess because they are larger than other files. But it does not take much effort to pack all the jar files and unzip them after installation.

• The .pack extension assumes they are packaged but not gzipped. Again, why won't Oracle do gzip? for example, with packaging, rt.jar reduces the size from 45 MB to 12 MB, and adding gzip also reduces it to 6 MB.

Answer 1

Some of the jar files mentioned are listed as location, language, or machine. Perhaps Oracle includes several versions in the package files for the installer to choose from? This can be tested by unpacking the .pack files. Oracle can use a tool for batch installers, which includes static as-is files (i.e. jar files), but includes specific things like .pack files. Just some ideas may not be known without working there.