jni-maven

jni-maven is a sample project intended to be used as a template for Java applications using JNI.

Requirements

You'll need the following:

• JDK
• gcc
• maven
• ant
• make

Usage

git clone https://github.com/gkubisa/jni-maven.git jni-maven
cd jni-maven
mvn package
java -cp target/jni-maven-1.0-SNAPSHOT.jar ie.agisoft.App

How it works

maven-antrun-plugin is added to the process-classes phase of the build. It is used to:

• generate the C++ headers using javah. They are created in src/main/c++. I did not use javah ant target, because it assumes Sun JDK, while I'm using OpenJDK.
• run make to build the native code

The Makefile compiles the native code from src/main/c++ into *.o files which are stored in target/c++. Then it runs the linker which produces a single *.so object stored in target/classes.

Because the *.so file is in target/classes, it's included in the final JAR file. This way the whole project produces a single artifact and can be easily used as a dependency by other Maven projects.

The final bit is the custom module loader LibraryLoader.loadLibrary, which extracts the native library from the jar into a temporary file and loads it - the standard System.loadLibrary cannot do it.

Limitations / possible improvements

1. Native code build currently works only on Linux
2. Only C++ is supported as the native language
3. The paths in the Makefile are hard-coded. It would be nice to initialize them from Maven properties.

Patches welcome!

Credits

1. http://docs.codehaus.org/display/MAVENUSER/Projects+With+JNI - jni-maven is a simplified implementation of the concept presented in this article
2. http://code.google.com/p/jav8/ - LibraryLoader class in based on the code from this project (V8ScriptEngineFactory.java)