...
If your host architecture differs from LTSP chroot, you won't be able to install Java this way. Chrooting will make the chroot report the host's architecture to the installer, which causes it to download the wrong binary. Generally, chroots should be kept the same architecture as host, but if they must be different, one can still install Java this way if live-boot from the correct architecture media is done and chroot is entered from it.
...
Plugin
In some cases, the presence of IcedTea Java Browser plugin (OpenJRE implementation) will prevent Oracle Java plugin from working or even being installed.
...