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 the examples and jackson_core_test for some usage examples.

It is possible to specify some dependencies to be downloaded automatically through maven. When targetting Android, it's also possible to generate bindings for custom code depending on Android libraries.

Basic features of the Java language (static and instance methods, fields, constructors) are supported in generated bindings.

Basics #

Running jnigen #

There are 2 ways to use jnigen:

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

Both approaches are almost identical. When 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. (Re)generate the bindings by running dart run jnigen --config jnigen.yaml in the root of the respective examples. Corresponding README files contain more information about the examples.