Inside this repository you can find JNI related codes that I have collected over years of working with JNI. You can also find a companion book, where I describe some topics in details. JNI Cookbook page can be found here: JNI Cookbook

Building and running

The easiest way to build and run codes is to clone the repo and run all tests.

> git clone https://github.com/mkowsiak/jnicookbook.git
> cd jnicookbook/recipes
> make all
> make test
> make clean

Remember that you can always run each and every sample separatelly. Simply call make inside given recipe. Let's say you want to run recipeNo001. All you have to do is to run

> cd jnicookbook/recipes/recipeNo001
> make
/Library/Java/JavaVirtualMachines/jdk-14.jdk/...
...
> make test
/Library/Java/JavaVirtualMachines/jdk-14.jdk/...
library: :./lib
Hello world!

Ready for Java 8 and onwards

JNI Cookbook samples were adapted to Java 14 release. You shouldn't experience any issues while working with most recent release of Java. If you have stuck with Java 8 - for any reasons - you should be able to use samples as well.

JNI Cookbook samples were tested with:

• JDK 1.8
• JDK 9
• JDK 10
• JDK 11
• JDK 12
• JDK 13
• JDK 14

Debugging

Debugging JNI code is not quite like sitting on cloud nine. You have to attach to JVM where JNI code is running and debug native code using external tools (e.g.: gdb, CLion). When it comes to debugging JNI code, you can find some hints inside JNICookbook as well. Even more, you can find a screencast that demonstates how to debug JNI code using IntelliJ IDEA and CLion

Requirements

At the moment, JNI Cookbook targets Linux and macOS. It should work on both platforms without any issues.

Setting up macOS system for JNI Cookbook

Make sure to install XCode. Once installed, perform installation of Command Line Tools.

Make sure to install OpenJDK or Java SE Development Kit 13).

Once installed, make sure to set JAVA_HOME following way

export JAVA_HOME=$(/usr/libexec/java_home -v 13)

If you are one of those brave people, you can use the most recent version of OpenJDK - JDK 14.

Once installed, make sure to set JAVA_HOME following way

export JAVA_HOME=$(/usr/libexec/java_home -v 14)

Setting up Ubuntu system for JNI Cookbook

sudo apt install openjdk-13-jdk
sudo apt install git
sudo apt install make
sudo apt install gcc
sudo apt install g++

# Inside JNI Cookbook, all the Java stuff is based on JAVA_HOME
# variable - you need it inside the env.
export JAVA_HOME=`readlink -f $(which java) | sed 's|/bin/java||'`

# We need ./lib on LD_LIBRARY_PATH
# Rememer that inside JNI code we no longer use java.library.path
# when it comes to resolving location of the shared library.
# Inside JNI we base on system's way of locating the lib.
export LD_LIBRARY_PATH=./lib:${LD_LIBRARY_PATH}

Setting up Scala

JNI Cookbook contains Scala based samplesi. These samples are using JNA to call native code. Please make sure to install most recent version of Scala and sbt. This will allow you to avoid following error:

Exception in thread "main" java.io.IOError: 
    java.lang.RuntimeException: /packages cannot be represented as URI

At the time of writing these versions were, respectivelly: Scala 2.13.1 and sbt 1.3.7.

Nobody has time for that!

Are you crazy? Do you think I have time for all that setup?

You are right, nobody has time for that. This is why this product comes with self sufficient, ready for immediate use, Docker file. Once you start the container, everything is there. All you have to do is to build the image and run the container.

> cd docker
> docker build -t jnicookbook .
> docker run -it jnicookbook

that's it. That's all you have to do, to get all the JNI Cookbook samples ready for testing.

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