ok, i poked around in the java8 folder and found another folder with some more files and the executable.
now it works. thanks for your help and patience. for those who maybe struggling with the same issue, the path that worked for me:
/volume1/@appstore/java8/ejdk1.8.0_51/linux_i586/jre/bin/java ...

at least something, erroris a little bit different :)
/usr/bin/filebot: line 41: /volume1/@appstore/java8/ejdk1.8.0_51/bin/java: not found

fyi the content:
DiskStation> cd /volume1/@appstore/java8/ejdk1.8.0_51/bin
DiskStation> dir
drwxr-xr-x 2 root root 4096 Jun 25 19:49 .
drwxr-xr-x 6 root root ...

in a weired way this is good news - i am not that incompetent
but, as you know by now, i am not a linux/code/ssh crack...
vi filebot.sh .... so far so good. and now, cant find the exact location where to put the java path (/volume1/@appstore/java8/ejdk1.8.0_51/bin/java)

....thx. but still a missing java.
/usr/bin/filebot: line 41: java: not found

Status quo:
DiskStation> java -version
java version "1.8.0_51"
Java(TM) SE Embedded Runtime Environment (build 1.8.0_51-b07, headless)
Java HotSpot(TM) Embedded Server VM (build 25.51-b07, mixed mode)
DiskStation> cd ...

ok, i startet from scratch and followed your yt-tutorial. everything is working out until this point:
downlod ok - extract with "tar -zxvf java.tar.gz" (ds is extracting something)

next step: ls command - my result is different to the video:
DiskStation> ls
jrecreate.bat jrecreate.config ...

hey guys,

i am struggling with the same problem.heres what i did so far:
(DS 415+ latest DSM)
• installing java 8
DiskStation> java -version
java version "1.8.0_51"
Java(TM) SE Embedded Runtime Environment (build 1.8.0_51-b07, headless)
Java HotSpot(TM) Embedded Server VM (build 25.51-b07, mixed ...