JNI Getting Start#

Reference Links#

• http://web.archive.org/web/20120419230023/http://java.sun.com/docs/books/jni/html/start.html
• https://zauner.nllk.net/post/0013-jni-and-the-java-library-path/

So, let's go!

1. Create a Java Class#

class HelloWorld {
     private native void print();
     public static void main(String[] args) {
         new HelloWorld().print();
     }
     static {
         System.loadLibrary("HelloWorld");
     }
 }

2. Comlile the Java Class#

javac HelloWorld.java

3. Generate the head file of c program#

javah -jni HelloWorld

4. Create the c program#

#include <jni.h>
#include <stdio.h>
#include "HelloWorld.h"

JNIEXPORT void JNICALL
Java_HelloWorld_print(JNIEnv *env, jobject obj)
{
     printf("Hello World!\n");
     return;
}

5. Compiler the c program into a shared library#

• CMakeLists.txt

cmake_minimum_required(VERSION 3.10)

project(java_hello VERSION 1.0.1)

include_directories(/usr/lib/jvm/java-8-openjdk-amd64/include /usr/lib/jvm/java-8-openjdk-amd64/include/linux)

add_library(HelloWorld SHARED HelloWorld.c)

mkdir build && cd build
cmake ..
make

6. Run the Java Program#

java -Djava.library.path=./build HelloWorld