A simple JNI example

tested on CentOS 5.8

Step 1: declare a native function in the java source file 

public class AddMe{        static {                System.loadLibrary("hello");        }        public native void sum(int a, int b);        public static void main(String[] args){                AddMe am = new AddMe();                am.sum(2, 5);        }}

Step 2: compile the java class

javac AddMe.java

Step 3: generate the c header file

javah -jni AddMe

You will find the "AddMe.h" file in the current working directory

Step 4: implement the c function "sum" (by JNI naming convention the function name would be Java_AddMe_sum)

We create a c source file called "addme.c"

#include "AddMe.h"#include <stdio.h>JNIEXPORT void JNICALL Java_AddMe_sum (JNIEnv *env, jobject obj, jint a, jint b){        jint result = 0;        result = a + b;        printf("hello world %d\n", result);}

Step 5: compile the c code and generate a share library "libhello.so" (it must have the name libhello so that System.loadLibrary("hello") can dynamically load the library)

gcc -fPIC -I/usr/lib/jvm/java/include -o libhello.so -shared ./addme.c

Step 6: run the java bytecode

java -Djava.library.path=. AddMe

Then you can see "hell world 7" printed on console