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dart/native.git/41e7871e/./pkgs/jni_gen
tree: f7eff302c0f1c7354763fff5f24e19304b73df82
  1. bin/
  2. cmake/
  3. examples/
  4. java/
  5. lib/
  6. test/
  7. .gitignore
  8. analysis_options.yaml
  9. LICENSE
  10. pubspec.yaml
  11. README.md
pkgs/jni_gen/README.md

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

Few runnable examples are provided in examples/ directory. These directories do not include generated code. Generate the bindings by running dart run jni_gen --config jnigen.yaml in the example project root. See the respective READMEs for more details.