RuntimeException: Package jdk.internal.jimage.decompressor in module jrt.fs and module java.base

Question

Component Details - Using IntelliJ IDEA 2017.1 CE and jdk-9-ea+154

main() -

Set<String> set2 = Set.of("a", "b", "c");
set2.forEach(System.out::println);

module-info.java

module collection {
    requires java.base;
}

Logs -

Error occurred during initialization of VM
java.lang.RuntimeException: Package jdk.internal.jimage.decompressor in both module jrt.fs and module java.base
    at jdk.internal.module.ModuleBootstrap.fail(java.base@9-ea/ModuleBootstrap.java:699)
    at jdk.internal.module.ModuleBootstrap.boot(java.base@9-ea/ModuleBootstrap.java:329)
    at java.lang.System.initPhase2(java.base@9-ea/System.java:1928)

Doubtful over the implementation of initialization of VM, my question is that I haven't included module jrt.fs - Where is it coming in the picture from? How do I debug such modules inclusion/exclusion? How do I further solve the current exception?

Answer 1

$JAVA_HOME/lib/jrt-fs.jar contains a copy of the "jrt" file system provider compiled to JDK 8. It's for tools such as IDEs that run on JDK 8 but need to access a JDK 9 run-time image.

From the exception then it does appear that this JAR file, or maybe $JAVA_HOME/lib, has been put on the module path in error. JAR files that do no contain a module-info.class in the top-level directory are treated as automatic modules so this is why the exception has "module jrt.fs" in the message. The exception basically just means that you've ended up with two modules containing the jdk.internal.jimage.decompressor package (and many other packages) due to putting jrt-fs.jar on the module path.