load H5's JNI library from the main code

[bogovicj]

This or something like it will be needed in updating n5-hdf5.
(with help from Claude)

[mkitti]

Thanks, moving the loading into the main code is the right fix: downstream code had no way to load hdf5_java itself. I built n5-hdf5 saalfeldlab/n5-hdf5#50 against this branch, and it passes with no workaround (47 tests, 5 skipped, same as its master).

Blocking: class-initialization order. Five public enums initialize their constants from HDF5Constants:

• IHDF5WriterConfigurator.FileFormatVersion
• HDF5DataClass
• HDF5StorageLayout
• HDF5EnumerationType.EnumStorageForm
• CharacterEncoding

If any of them, or anything using them, is touched before HDF5Factory/HDF5FactoryProvider/HDFHelper, HDF5Constants runs H5.loadH5Lib() before load(). H5's class initialization then fails, and since that's permanent in Java, every later HDF5 call fails too (UnsatisfiedLinkError: 'int hdf.hdf5lib.H5.H5dont_atexit()').

• CI: that's the 306 macOS failures here. HDF5ArchiverTest touches FileFormatVersionBounds first, and Linux passes only because of its test order. The removed NativeLibraryBootstrap used to hide it.
• Downstream: reading CharacterEncoding.UTF8 before HDF5Factory.open(...) fails the same way.
• Scope: initializing each class of the jar first in a fresh JVM, 15 of 1,104 classes break HDF5 this way.

Smaller:

• loaded = true is set before loading succeeds, so after one failure later callers skip load() silently and only see the error above.
• System.setProperty(..., Loader.load(...)) throws if Loader.load() returns null, which it does when JavaCPP's library loading is disabled.

I've put fixes for all three in #14, stacked on this PR: enum constants read HDF5 values through HDF5NativeLibrary.intConstant(() -> ...)/longConstant(...), which call load() first. With it, 0 of 1,104 classes fail. #14's CI passes on macOS and Linux (Java 8 and 21) without the bootstrap; Windows still fails only with the separate-HDF5-libraries error that bytedeco/javacpp-presets#1814 fixes.

Compatibility with javacpp-presets #1814: once bytedeco/javacpp-presets#1814 is in, hdf5_java's own static initializer also sets hdf.hdf5lib.H5.hdf5lib, to the same path. This PR is still needed after that, because something has to load hdf5_java first. The extra setProperty is just redundant.

🤖 Generated with Claude Code