If you are interested in stories with happy endings, you would better of reading some other book. In this book, not only there is no happy ending, there is no happy beginning, and very few happy things in the middle.

-- Lemony Snicket, The Bad Beginning

Inside this book you can find JNI related codes that I have written over years of working with JNI. I was typically preparing small samples to test some particular concepts. Sometimes, I was preparing solutions for people who were desparatelly looking for help on stackoverflow. There is a companion material in form of text, figures, where I describe some topics in details. JNI Cookbook page can be found here: JNI Cookbook. Please note that I had no time, yet, to prepare nice and detailed explanation for each end every contept that is tackled in this book.

Building and running

Seeing is believing. This is why I have decided to provide people with not only the description of some concepts, but with working sample code as well. The code you can find in this repository is an integral part of the book.

The easiest way to build and run codes is to clone the repository 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, TotalView, lldb). When it comes to debugging JNI code, you can find some hints inside JNI Cookbook as well. Even more, you can find a screencast that demonstates how to debug JNI code using IntelliJ IDEA and CLion. In fact, there are more to come. I plan to prepare one that will discuss lldb, one for gdb, and last but not least one for TotalView (this is, however, song of the future).

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 samples. 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.

It's no good reading about JNI in 2021

I won't force you to do so, but you are always welcome to read this book.

I think this book is bad

I think your book is not really that good (as some people say) and it's not interesting at all.

I totally agree. After all, this is a book related to low level coding. Have you ever read really interesting book that was describing low level coding? I really doubt it. These kind of books can be informative, they might be useful, but calling them entartaining, and really good books - that's euphemism.

Live is way too short to read dull books - like this one. This is why I have prepared a list of books you should have read instead. Each week, I will post a new book that is definitely more exciting and definitely worth way more of your time rather than this one. Stay tuned. List of books that are way more interesting.

I don't like your book

I can't make everybody happy. Make sure to double check previous points.

I think you should ...

No, thank you.

I think it would be better if ...