Import Converter as a Paclet

Question

In short, I have a package that can load a proprietary device file-format. The underlying reading code is written in Java, packed into .jar, and in a Mathematica package, I can use some simple JLink wrapper functions to access the functionality.

Now, I would like to attach my code to Mathematica's Import, which is usually also trivial by employing ImportExport`RegisterImport. However, to make the importer always available, the RegisterImport code is should be placed in

$UserBaseDirectory/SystemFiles/Formats/MyFormat/Import.m

For simplicity, assume the following fake package structure

MyFormat/
├── Java
│   └── reader.jar
├── Kernel
│   └── init.m
├── Import.m
├── PacletInfo.m
└── ReadingFunctions.m

In ReadingFunctions.m, I'm accessing the Java methods from the jar and provide high-level Mathematica functions for the binary file format. In Import.m I can use these functions and register a custom importer.

My questions are simple:

1. How can I set-up the PacletInfo.m so that the Import.m goes into the Formats directory and automatically loads the rest of the package when I try to import files?
2. Or should I use Loading -> "Startup" in the PacletInfo.m to make it available on a kernel start? But then, some unnecessary is always evaluated (e.g. loading of the jar) that I only need if I indeed use the importer in a session.

Are there other/better ways I haven't considered? I could start testing around, but my hope is that someone can give some hints.

Bonus: Do we have a better alternative to this here for adding a file-extension so that it is automatically recognized by Import?

Answer 1

@halirutan you can now register the format extension using this function from Wolfram Function Repository:

https://resources.wolframcloud.com/FunctionRepository/resources/RegisterFormat

Answer 2

1. I don't think there's a way for PacletInfo.m to do this directly, but how about adding something in init.m like this before the Get[]:

   CreateDirectory[FileNameJoin[{$UserBaseDirectory, "SystemFiles", "Formats", "MyFormat"}]];
   Export[FileNameJoin[{$UserBaseDirectory, "SystemFiles", "Formats", "MyFormat", "Import.m"}], "RegisterImport...", "Text"];
   

2. Rather than registering the paclet functions as a format directly, make a small wrapper that does this, and register myImport instead:

   myImport[filePath_String, opts : OptionsPattern[]] :=
   Block[{..},
       Needs["MyFormat`"];
       ...
   ]
   

I noted in the comment above that there's no way to hook up to FileFormat (and thus get auto detection of extension/format the proper way) right now so the extension method from this post is the best bet in V11.3