Java interop using package:jnigen
Dart mobile, command-line, and server apps running on the Dart Native platform, on Android, Windows, macOS, and Linux can use package:jni
and package:jnigen
to call Java and Kotlin APIs.
package:jni
allows Dart code to interact with Java through JNI. However, doing so involves a lot of boilerplate code, so you can use package:jnigen
to automatically generate the Dart bindings for a given Java API.
You can compile Kotlin to Java bytecode, allowing package:jnigen
to generate bindings for Kotlin as well.
Simple Java example
#This guide walks you through an example that uses package:jnigen
to generate bindings for a simple class.
Prerequisites
#- JDK
- Maven
Configure jnigen
#First, add package:jni
as a dependency and package:jnigen
as a dev dependency.
$ dart pub add jni dev:jnigen
Next, create a top-level file called jnigen.yaml
. This file contains the configuration for generating the bindings.
output:
dart:
path: lib/example.dart
structure: single_file
source_path:
- 'java/'
classes:
- 'dev.dart.Example'
path
specifies the path for the generated dart
bindings.
source_path
specifies the path of the Java source file that you want to generate bindings for, and classes
specifies the Java class.
java/dev/dart/Example.java
contains a very simple class, which has a public static method called sum
:
package dev.dart;
public class Example {
public static int sum(int a, int b) {
return a + b;
}
}
Generate the Dart bindings
#To generate the Dart bindings, run jnigen
and specify the config file using the --config
option:
$ dart run jnigen --config jnigen.yaml
In this example, this generates lib/example.dart, just as you specified in jnigen.yaml
.
This file contains a class called Example
, which has a static method called sum
, just like the Java file.
Use the bindings
#Now you're ready to load and interact with the generated library. The example app, bin/sum.dart, gets two numbers as arguments and prints their sum. Using the Example.sum
method is identical to Java.
// a and b are integer arguments
print(Example.sum(a, b));
Run the example
#Before running the example, you must build the dynamic library for jni
. The Java sources also must be compiled. To do so, run:
$ dart run jni:setup
$ javac java/dev/dart/Example.java
Now you can run the example:
$ dart run jnigen_example:sum 17 25
Which outputs 42
!
More examples
#The following are some more comprehensive examples of using package:jnigen
:
Example | Description |
---|---|
in_app_java | Demonstrates how to include custom Java code in a Flutter application and call it use jnigen . |
pdfbox_plugin | Example of a Flutter plugin that provides bindings to the Apache PDFBox library. |
notification_plugin | Example of a reusable Flutter plugin with custom Java code that uses Android libraries. |
Unless stated otherwise, the documentation on this site reflects Dart 3.5.0. Page last updated on 2024-05-22. View source or report an issue.