Set DefaultFileSystemProvider for testing

Question

How can I set the DefaultFileSystemProvider to use, for example, JimfsFileSystemProvider? The javadoc for FileSystems.getDefault() says I need to set a system property, but when I try to do that I get a NoSuchMethodException:

System.setProperty("java.nio.file.spi.DefaultFileSystemProvider",
                   "com.google.common.jimfs.JimfsFileSystemProvider");
FileSystems.getDefault();

Stack Trace:

java.lang.Error: java.lang.NoSuchMethodException: com.google.common.jimfs.JimfsFileSystemProvider.<init>(java.nio.file.spi.FileSystemProvider)
at java.nio.file.FileSystems$DefaultFileSystemHolder.getDefaultProvider(FileSystems.java:128)
....

Do I need to set up something else or is this a bug in jimfs?

Guidry

Needing to set the default file system is generally an anti-pattern, and intentionally not implemented by the Jimfs team. See Kevin Bourrillion's comment on Guava's Google+ post announcing Jimfs. – Vend

@Vend looks like a broken link – Deidredeific

@Deidredeific just tried it, it loads fine for me. – Vend

@Vend Really.....interesting. Maybe it's something with the proxy/firewall settings where I work. Sorry about that. – Deidredeific

Kevin Bourrillion said: "We don't think that is the right way to go -- mutating global static state causes a huge mess. Instead, stop writing code that depends on the default file system. When code can accept a Path and work off its implicit fs, great; otherwise have the FileSystem itself injected. (Also, stop writing code that depends on the system default anything! )" – Carrigan

Answer 1

The javadoc of FileSystems.getDefault() states that:

...the default FileSystemProvider is instantiated by invoking a one argument constructor whose formal parameter type is FileSystemProvider.

Since JimfsFileSystemProvider does not have such constructor, you can't set it as the default file system.

This is exactly what the error means that you get:

java.lang.Error: java.lang.NoSuchMethodException: com.google.common.jimfs.JimfsFileSystemProvider.<init>(java.nio.file.spi.FileSystemProvider)

The method <init> is the constructor, and no constructor found with parameters java.nio.file.spi.FileSystemProvider.

Cortes

I guess that's the correct answer. However, it would be nice if Jimfs would support that... – Guidry