Log of instructions for JNI

Reference:

• Java Native Interface: Programmer's Guide and Specification

Edit HelloWorld.java

HelloWorld.java

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

Compile the JAVA class -- HelloWorld.class

  $ javac HelloWorld.java

Generate the NATIVE header file -- HelloWorld.h

  $ javah -jni HelloWorld

HelloWorld.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class HelloWorld */

#ifndef _Included_HelloWorld
#define _Included_HelloWorld
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     HelloWorld
 * Method:    print
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_HelloWorld_print
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

Implement the NATIVE method -- HelloWorld.c

HelloWorld.c

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

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

Compile the NATIVE source code and build the NATIVE library

  $ gcc -c -fPIC HelloWorld.c -I$JAVA_HOME/include -I$JAVA_HOME/include/linux
  $ gcc -shared HelloWorld.o -o libHelloWorld.so

Add "current" directory to the search path of share libraries

  $ export LD_LIBRARY_PATH=.

Run the HelloWorld JAVA program

  $ java HelloWorld

Hello World