Java on the iPaq under Linux

Obtaining a JRE

The fine folks at Blackdown have compiled a version of Java 1.3.1 for ARM processors. I have created a script that compresses the JRE to fit on an unmodified iPaq.

Shrinking the JRE

In a standard JRE there are a lot of files that are unnecessary. In the root of the JRE install, the only things we need are the bin and the lib directories.

In bin, we don't need these files:

tnameserv
policyserv
keyserv
rmid
rmiregistry
armv4l/green_threads
armv4l/native_threads/tnameserv
armv4l/native_threads/policyserv
armv4l/native_threads/keyserv
armv4l/native_threads/rmid
armv4l/native_threads/rmiregistry

In lib, we don't need these files:

i18n.jar (Internationalization)
applet
font.properties.* (An article about font.properties files)
sunrsasign.jar
armv4l/green_threads
audio (soundbank)
cmm/PYCC.pf (Color Management)

rt.jar

We also need to shrink rt.jar.

Removed from our JAR file:

java/rmi
java/applet
org (CORBA)
com/sun/corba
com/sun/rmi
sun/rmi
sun/applet
javax/accessibility
javax/sound
javax/rmi

Tips

If you develop with a 1.4 JDK but deploy to the 1.3 JRE, you may run into these problems:

Calendar.getTimeInMillis() is public in 1.4, but wasn't in 1.3. This will cause an IllegalAccessError when you run your code on the iPaq even though it runs fine under the 1.4 JRE on your development system.

Last modified on 21 Dec 2005 by AO