Questions about the Jigsaw EA builds

Stephane Epardaud stef at
Fri Nov 27 13:51:05 UTC 2015


I work on Ceylon, a JVM language, using a fork of javac 7 with backports
from javac 8, and currently trying to see how to make it work with Java
9, which is interesting in our case as Ceylon already has modularity and
adopted the JDK modularisation (as it was planned in Jigsaw) since Java 7.

I downloaded the EA builds from and it lists two:

- (build 93)
- (build 86)

Leading me to believe that the first was more recent, but it does not
appear to include the java.annotations.common module in its lib/modules
jimages. The second one has it, but has other differences such as having
a jmods/ folder with ZIP module files (the format seems to be
straightforward, but is there a specification somewhere?), and having
only a single .jimage in lib/modules (but with more modules there).

Am I right that I should use the second one?

How do the build numbers relate? Are they independent ?

Is the lib/modules supposed to contain one or three .jimage files?

How does that relate to the jmods/ folder? Will/should javac use the
.jimage or the jmods files? They seem to offer the same contents.

Is there any documentation as to the format of the "jrt:/" NIO
FileSystem? I've figured some things out to extract class file data from
there, but a specification (even WIP) would be useful to verify my

Thanks for you help, cheers.

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