ax-filesystem

Alexandria FileSystem

This module provides a set of generic base classes to make it easier to write your own FileSystemProvider. The ax-fileystem-memory module is a usable, working example of how to use this module. While this module is licensed under Apache 2.0, the ax-fileystem-memory license is less restrictive so that you may copy it.

Creating a FileSystemProvider

So you want to create a FileSystemProvider... That's one of the main reasons we created ax-fileystem-memory, and this module, on which that one is built.

You've probably seen the guide from oracle or any number of pieces of example code. The critical thing missing from many of these pages is fully-fledged example code. The oracle guide refers to the ZipFileSystemProvider which you probably wouldn't want to copy, and other examples like githubfs are implementation specific enough that they would be hard to copy.

ax-fileystem-memory is simple, and we have tried to create a maximum of re-usable code in a this module. Here are the rough steps we suggest when you want to create your own filesystem provider:

1. Take a look at the the javadocs for the classes you will need to implement:

• FileSystemProvider
• FileSystem
• Path

2. At least skim the guide from oracle so you understand terms.
3. Set up your project

• Create your maven module
• Add a dependency on com.g2forge.alexandria:ax-filesystem so you can use our generic base classes
• Add a test scoped dependency on com.g2forge.alexandria:ax-filesystem-test so you can use our file system unit tester (test driven development is most fun when someone else writes the tests)

4. Copy the unit tests in your src/test/java package

• Modify the before() method to create an instance of your file system
• Modify the createPath() method to create paths associated with the file system created by before()
• Depending on how you decide to format your URIs, you may only need to update MYFS to your scheme (replace memory:... with MYFANCYNEWFS:...).

5. Run JUnit and watch everything fail because you haven't implemented anything. This'll make it more fun later when you implement things.
6. Create your FileSystemProvider by extending AGenericFileSystemProvider

• You can copy MemoryFileSystemProvider
  • At a minimum you'll need to change the getScheme() return value to your new scheme. This way you'll have a fully functional memory file system provider, separate from ours.
• You may find it easier to start from an empty class and fill in implementations, watching your unit test pass rate increase as you go.

MemoryFileSystemProvider is implemented using AGenericFileSystemProvider. This means you will need to implement:

• A class for URIs
• All the basic file system operations like createDirectory(), delete(), etc.
• Some kind of code to represent entries, files and directories in your file system, and IGenericEntryAccessor to allow the base classes to interact with this.
• File attributes using IAttributeViewAccessor

You will not need to implement:

• FileSystem, though you can write a custom one the easiest way will be to use GenericFileSystem
• Path, though you can write a custom one the easiest way will be to use GenericPath
• Code to handle locking and atomicity, or basic file time modifications