Hi,
I use Cygwin emacs with Windows UI. I have just installed java 8 (but java 6 is still present for some legacy application) and updated my .bash_profile with the following:
export JAVA_HOME=/cygdrive/c/tools/java8
export PATH=$PATH:$JAVA_HOME/bin
Org is configured to run ditaa code blocks, but when I evaluate a code block, I see the following in the *Message* buffer
executing Ditaa code block (TEST)...
java -Dfile.encoding=UTF-8 -jar /cygdrive/c/Users/re/.emacs.d/site-lisp/org-9.0.4/contrib/scripts/ditaa.jar /tmp/babel-6316MOI/ditaa-63168iW /cygdrive/c/Users/re/pics/test.png
Error: Unable to access jarfile /cygdrive/c/Users/re/.emacs.d/site-lisp/org-9.0.4/contrib/scripts/ditaa.jar
Code block evaluation complete.
I am using Org 9.0.4 downloaded today.