Error "Java" and "C" integration through JNI

Question

Personal I am not managing to consume functions of a lib in "C" using Java with JNI. Follow my artifacts and the error generated.

Class CalculadoraJNI:

public class CalculadoraJNI {
    // Declaração do método nativo:
    public native int calcula (int num1, int num2);
    static {
        System.loadLibrary("calcula");
    }

Filing cabinet TesteCalculadoraJNI.java

public class TesteCalculadoraJNI {
    public static void main (String args[]) {
        CalculadoraJNI calc = new CalculadoraJNI();

        int num1 = Integer.parseInt(args[0]);
        int num2 = Integer.parseInt(args[1]);

        int resultado = calc.calcula(num1, num2);
        System.out.println("A soma é: " + resultado);
    }
}

After class construction I executed the following sequence of commands:

javac CalculadoraJNI.java
javac TesteCaculadoraJNI.java
javah CalculadoraJNI

File generated by the javah Caculadorajni command

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

    #ifndef _Included_CalculadoraJNI
    #define _Included_CalculadoraJNI
    #ifdef __cplusplus
    extern "C" {
    #endif
    /*
     * Class:     CalculadoraJNI
     * Method:    calcula
     * Signature: (II)I
     */
    JNIEXPORT jint JNICALL Java_CalculadoraJNI_calcula
      (JNIEnv *, jobject, jint, jint);

    #ifdef __cplusplus
    }
    #endif
    #endif

Filing cabinet calculaJNI.c:

#include <stdio.h>
#include "CalculadoraJNI.h"

/*
* Método que executa a soma
*/
int calcula (int num1, int num2) {
    int resultado = num1 + num2;
    return resultado;
}

/*
* Método com a mesma assinatura do calculadoraJNI.h
*/
JNIEXPORT jint JNICALL Java_CalculadoraJNI_calcula
        (JNIEnv * env, jobject jobj, jint num1, jint num2)
{
    return calcula (num1, num2);
}

Compilation of code "C":

gcc -o libcalcula.so -shared -I/usr/lib/jvm/java-7-openjdk-amd64/include calculaJNI.c -fPIC

Error generated when trying to run:

Exception in thread "main" java.lang.UnsatisfiedLinkError: no calcula in java.library.path
    at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1886)
    at java.lang.Runtime.loadLibrary0(Runtime.java:849)
    at java.lang.System.loadLibrary(System.java:1088)
    at CalculadoraJNI.<clinit>(CalculadoraJNI.java:5)
    at TesteCalculadoraJNI.main(TesteCalculadoraJNI.java:3)

Answer 1

First of all, you should check that the parameter passed in the System.loadLibrary method is correct and that the library actually exists. Note that the library extension is not required. Thus, if your library is named Samplelibrary.dll, you must pass the Samplelibrary value as a parameter.

Also, in case the library is already loaded by the application and the application tries to load it again, the Unsatisfiedlinkerror will be released by JVM. Also, you should check that the native library is present either in java.library.path or in your application’s PATH environment library. If the library cannot be found yet, try providing an absolute path to the System.loadLibrary method.

To run the application, use the -Djava.library.path argument to explicitly specify the native library. For example, using the terminal (Linux or Mac) or command prompt (Windows), run the application by issuing the following command:

java -Djava.library.path = "" -jar