thufir@arrakis:~$ 
thufir@arrakis:~$ cat /var/lib/gems/1.8/gems/rjb-1.1.2/ext/gem_make.out
ruby extconf.rb install rjb
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=/usr/bin/ruby1.8
extconf.rb:33: JAVA_HOME is not directory. (RuntimeError)
thufir@arrakis:~$ 
thufir@arrakis:~$ echo $JAVA_HOME
/usr/lib/jvm/java-6-sun/jre/bin/java
thufir@arrakis:~$ 
thufir@arrakis:~$