Changing the default file system provider is broken :(

Sat Apr 22 11:20:15 UTC 2017

Ooops !
if you use the module path, you can not change the default system provider mechanism anymore,
mostly because the module implementation internally uses java.nio.file.Path at different places.

First, trying to initialize the default system provider in Java code do not work at all,
calling
  System.setProperty("java.nio.file.spi.DefaultFileSystemProvider", "...");
in a main does nothing because the jigsaw implementation has already loaded the default implementation to be able to inspect the modules.

Then, if you try to use the command line
 -Djava.nio.file.spi.DefaultFileSystemProvider=...
you have various bootstrapping issues.

With exploded modules, when trying to initialize the default file system, the part of jigsaw that reads exploded modules uses path.toFile() that fails it checks that the path belongs to the default file system which is not already initialized
(see below for the whole stacktrace)

With modular jars, when trying to initialize the default file system, the JarModuleReader also uses path.toFile(), leading to the same error

One way to solve that is to change the code in FileSystems.getDefault() to add a nullcheck,
        FileSystem defaultFileSystem = DefaultFileSystemHolder.defaultFileSystem;
        if (jdk.internal.misc.VM.isBooted() && defaultFileSystem != null) {
            return defaultFileSystem;
        } else {
            return BuiltinFileSystemHolder.builtinFileSystem;
        }
Another solution is to change the code of jigsaw to only use the builtinFileSystem, delaying the initialization of the default system which will also solve the case where an application uses System.setProperty.

cheers,
Rémi

Stacktrace with exploded modules:
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.Error: java.lang.UnsupportedOperationException: Path not associated with default file system.
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.getDefaultProvider(FileSystems.java:139)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.access$100(FileSystems.java:100)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder$1.run(FileSystems.java:109)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder$1.run(FileSystems.java:107)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.defaultFileSystem(FileSystems.java:107)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.<clinit>(FileSystems.java:101)
	at java.base/java.nio.file.FileSystems.getDefault(FileSystems.java:188)
	at java.base/java.nio.file.Path.toFile(Path.java:655)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.newJarFile(ModuleReferences.java:229)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.<init>(ModuleReferences.java:239)
	at java.base/jdk.internal.module.ModuleReferences.lambda$newJarModule$0(ModuleReferences.java:96)
	at java.base/jdk.internal.module.ModuleReferenceImpl.open(ModuleReferenceImpl.java:88)
	at java.base/jdk.internal.loader.BuiltinClassLoader.createModuleReader(BuiltinClassLoader.java:953)
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1719)
	at java.base/jdk.internal.loader.BuiltinClassLoader.moduleReaderFor(BuiltinClassLoader.java:945)
	at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:702)
	at java.base/jdk.internal.loader.BuiltinClassLoader.findClassInModuleOrNull(BuiltinClassLoader.java:651)
	at java.base/jdk.internal.loader.BuiltinClassLoader.findClass(BuiltinClassLoader.java:532)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:585)
	at java.base/java.lang.Class.forName(Class.java:447)
	at java.base/sun.launcher.LauncherHelper.loadModuleMainClass(LauncherHelper.java:585)
	at java.base/sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:523)
Caused by: java.lang.UnsupportedOperationException: Path not associated with default file system.
	at java.base/java.nio.file.Path.toFile(Path.java:658)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.newJarFile(ModuleReferences.java:229)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.<init>(ModuleReferences.java:239)
	at java.base/jdk.internal.module.ModuleReferences.lambda$newJarModule$0(ModuleReferences.java:96)
	at java.base/jdk.internal.module.ModuleReferenceImpl.open(ModuleReferenceImpl.java:88)
	at java.base/jdk.internal.loader.BuiltinClassLoader.createModuleReader(BuiltinClassLoader.java:953)
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1719)
	at java.base/jdk.internal.loader.BuiltinClassLoader.moduleReaderFor(BuiltinClassLoader.java:945)
	at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:702)
	at java.base/jdk.internal.loader.BuiltinClassLoader.findClassInModuleOrNull(BuiltinClassLoader.java:651)
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:576)
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:550)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:473)
	at java.base/java.lang.Class.forName0(Native Method)
	at java.base/java.lang.Class.forName(Class.java:374)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.getDefaultProvider(FileSystems.java:129)
	... 22 more

StackTrace with modular jars:
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.Error: java.lang.UnsupportedOperationException: Path not associated with default file system.
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.getDefaultProvider(FileSystems.java:139)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.access$100(FileSystems.java:100)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder$1.run(FileSystems.java:109)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder$1.run(FileSystems.java:107)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.defaultFileSystem(FileSystems.java:107)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.<clinit>(FileSystems.java:101)
	at java.base/java.nio.file.FileSystems.getDefault(FileSystems.java:188)
	at java.base/java.nio.file.Path.toFile(Path.java:655)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.newJarFile(ModuleReferences.java:229)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.<init>(ModuleReferences.java:239)
	at java.base/jdk.internal.module.ModuleReferences.lambda$newJarModule$0(ModuleReferences.java:96)
	at java.base/jdk.internal.module.ModuleReferenceImpl.open(ModuleReferenceImpl.java:88)
	at java.base/jdk.internal.loader.BuiltinClassLoader.createModuleReader(BuiltinClassLoader.java:953)
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1719)
	at java.base/jdk.internal.loader.BuiltinClassLoader.moduleReaderFor(BuiltinClassLoader.java:945)
	at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:702)
	at java.base/jdk.internal.loader.BuiltinClassLoader.findClassInModuleOrNull(BuiltinClassLoader.java:651)
	at java.base/jdk.internal.loader.BuiltinClassLoader.findClass(BuiltinClassLoader.java:532)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:585)
	at java.base/java.lang.Class.forName(Class.java:447)
	at java.base/sun.launcher.LauncherHelper.loadModuleMainClass(LauncherHelper.java:585)
	at java.base/sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:523)
Caused by: java.lang.UnsupportedOperationException: Path not associated with default file system.
	at java.base/java.nio.file.Path.toFile(Path.java:658)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.newJarFile(ModuleReferences.java:229)
	at java.base/jdk.internal.module.ModuleReferences$JarModuleReader.<init>(ModuleReferences.java:239)
	at java.base/jdk.internal.module.ModuleReferences.lambda$newJarModule$0(ModuleReferences.java:96)
	at java.base/jdk.internal.module.ModuleReferenceImpl.open(ModuleReferenceImpl.java:88)
	at java.base/jdk.internal.loader.BuiltinClassLoader.createModuleReader(BuiltinClassLoader.java:953)
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1719)
	at java.base/jdk.internal.loader.BuiltinClassLoader.moduleReaderFor(BuiltinClassLoader.java:945)
	at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:702)
	at java.base/jdk.internal.loader.BuiltinClassLoader.findClassInModuleOrNull(BuiltinClassLoader.java:651)
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:576)
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:550)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:473)
	at java.base/java.lang.Class.forName0(Native Method)
	at java.base/java.lang.Class.forName(Class.java:374)
	at java.base/java.nio.file.FileSystems$DefaultFileSystemHolder.getDefaultProvider(FileSystems.java:129)
	... 22 more