2017/11/16 15:03:37 -0800, Thomas Brand <t...@trellis.ch>: > this is my first post here, I hope this is the right place to ask a > question about how to use jlink.
Yes, it is! > For a given scenario with modules a and b, a using methods of b, following > instructions I managed to create a runnable image that can be called (from > inside exploded image) like > > $ ./bin/java a.A > A.main() called > B() called > string from B:test() > > this works nicely, also both modules are shown with > $ ./bin/java --list-modules > a > b > java.base@10-internal > > My question is if it's possible to create that image if module b would be > a legacy jar with just the .class files in it. No. There's no place in the image to store arbitrary JAR files, and even if there were there'd be no way to guarantee that all the other JAR files required by those JAR files are present, since they're just JAR files rather than modules. An image built by jlink is intended to be complete, consistent, and runnable as-is rather than something that might need additional JAR files just in order to launch. > I understand it's possible > to auto-generate the module-info.java for this legacy b.jar. > > I was thinking to be smart and just compile the generated module-info.java > for b.jar and then put it to the legacy b.jar or put the module-info.class > to the classpath in order to make it modular and then use for the jlink > step. > However that doesn't work: > > $JAVAC -d compile_out src/modb/module-info.java > src/modb/module-info.java:2: error: package is empty or does not exist: b > exports b; > ^ > 1 error To make this work, copy the content of b.jar into compile_out before you run javac so that the compiler can detect that the package is not empty. > How can a legacy jar file without access to source files be used as a > module, is it possible at all? The idea is to use legacy jar files in > conjunction with jlink to be used in self-contained runtime images. It's possible, as above, but it can fail in many ways. If the legacy JAR files contain conflicting packages then the module system won't be able to load them. Your generated module-info.java files could have missing dependences, especially if any of the legacy code uses reflection. It's really best to modularize an existing component properly, at the source. If you can't do that, for whatever reason, then it's generally safer to leave legacy JAR files on the class path. You can still use jlink to generate a custom image containing just the modules that you need; you'll just have to run that image with a non-empty class path. - Mark
