Experimental generator for FFI+JNI bindings.

This package will generate JNI code to invoke Java from C, and Dart FFI bindings to invoke this C code. This enables calling Java code from Dart.

This is a GSoC 2022 project.

Currently this package is highly experimental and proof-of-concept. See test/jackson_core_test for an example of generating bindings for a library. It is possible to specify some dependencies to be downloaded automatically through maven.

Basics

Running jni_gen

There are 2 ways to use jni_gen:

• Import package:jni_gen/jni_gen.dart from a script in tool/ directory of your project.
• Run as command line tool with a YAML config.

Both approaches are almost identical. If using YAML, it's possible to selectively override configuration properties with command line, using -Dproperty.name=value syntax.

Generated bindings

Generated bindings will consist of 2 parts - C bindings which call JNI, and Dart bindings which call C bindings. The generated bindings will depend on package:jni for instantiating / obtaining a JVM instance.

The following properties must be specified in yaml.

• c_root: root folder to write generated C bindings.
• dart_root: root folder to write generated Dart bindings (see below).
• library_name: specifies name of the generated library in CMakeFiles.txt.

The generated C file has to be linked to JNI libraries. Therefore a CMake configuration is always generated which builds the generated code as shared library. The init.dart in generated dart code loads the library on first time a method is accessed. On dart standalone, it will be loaded from the same directory specified in Jni.spawn call.

Examples

See jackson_core_test folder for an example how bindings are generated. Runnable examples will be added soon.