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facebookincubator/fbjni

A C++ helper library that simplifies calling Java code from native code through the Java Native Interface (JNI).

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Last commit
6 hours ago

What is it?

fbjni wraps the raw Java Native Interface in C++ helpers, so native code can call Java methods, fields and constructors with less boilerplate. It handles JNI local and global reference lifetimes automatically and translates exceptions between Java and C++ in both directions, so developers do not have to check exception state after every call.

Type conversion is handled by the library as well. Method descriptors are inferred from C++ signatures, and common types such as std::string convert to and from Java types. Java classes are mapped to C++ structs that derive from a JavaClass template and declare their Java descriptor.

The helpers were built to support cross-platform mobile code on Android, but the design has no Android-specific dependencies and works with any Java VM that supports JNI. The project includes documentation covering setup for Android builds, a quick reference of features and the rationale for using a JNI wrapper.

Key features

  • 01Automatic management of JNI local and global references.
  • 02Two-way translation of Java exceptions and C++ exceptions.
  • 03Method descriptors inferred from C++ function signatures.
  • 04Automatic conversion between std::string and Java strings.
  • 05Java classes mapped to C++ types through a JavaClass template.

Use cases

  • Calling Java APIs from a shared C++ codebase in an Android app.
  • Embedding native C++ modules in any JVM application that uses JNI.
  • Reducing manual reference counting and exception checks in existing JNI code.

Quick start

  1. 1

    Read the quick reference for copy-paste usage examples in docs/quickref.md

  2. 2

    Follow the Android build setup guide in docs/android_setup.md

In collections

Android apps & phone tools

Topics

#jni#java#cpp#android#native-interop#cross-platform

FAQ

What is fbjni?
A C++ helper library that simplifies calling Java code from native code through the Java Native Interface (JNI). fbjni wraps the raw Java Native Interface in C++ helpers, so native code can call Java methods, fields and constructors with less boilerplate. It handles JNI local and global reference lifetimes automatically and translates exceptions between Java and C++ in both directions, so developers do not have to check exception state after every call.
Is fbjni free to use? What license does it have?
fbjni is open source under the Apache-2.0 license. Check the license terms before using it in commercial products.
Is fbjni still maintained?
Actively maintained. The last commit to fbjni was on Oct 22, 2026.
What can I use fbjni for?
Calling Java APIs from a shared C++ codebase in an Android app. Embedding native C++ modules in any JVM application that uses JNI. Reducing manual reference counting and exception checks in existing JNI code.
How do I install fbjni?
Read the quick reference for copy-paste usage examples in docs/quickref.md Follow the Android build setup guide in docs/android_setup.md
Where can I get fbjni?
The source code and installation instructions are on GitHub: https://github.com/facebookincubator/fbjni

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