As for moving jdk instal to ramdisk, on can (ab)use the fact that in Debian/Ubuntu /usr/lib/jvm/java-6-sun is a symbolic link to /usr/lib/jvm/java-6-sun-${version}/

So create a tmpfs and mount it under /usr/lib/jvm/java-6-sun

    sudo mount -t tmpfs -o size=200M,nr_inodes=2k,mode=0775,noatime,nodiratime tmpfs /usr/lib/jvm/java-6-sun
    cd /usr/lib/jvm/java-6-sun
    cp -a /usr/lib/jvm/java-6-sun-${version}/* .

Done. Of course, if you have more than one jdk installed, update-alternatives may be necessary