Link Error in Java

Question

I get the following error:

Exception in thread "main" java.lang.UnsatisfiedLinkError: model.JNIResultSet.getSpieler()[Lmodel/Spieler;
    at model.JNIResultSet.getSpieler(Native Method)
    at model.JNIResultSet.main(JNIResultSet.java:18)

My java classes look like this:

package model;

public class Spieler {
private String vorname;
private String nachname;
private int trikotnummer;


public Spieler(String vorname, String nachname, int trikotnummer) {
    this.vorname = vorname;
    this.nachname = nachname;
    this.trikotnummer = trikotnummer;
}
}

and

package model;

public class JNIResultSet {

public JNIResultSet() { }

public native Spieler[] getSpieler();

static {
    System.loadLibrary("spieler");
}

public static void main(String[] args) {
    JNIResultSet jni = new JNIResultSet();
    Spieler s[] = jni.getSpieler();
    System.out.println("Laenge: " + s.length);
}


}

My header file looks like that:

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

#ifndef _Included_model_JNIResultSet
#define _Included_model_JNIResultSet
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class:     model_JNIResultSet
* Method:    getSpieler
* Signature: ()[Lmodel/Spieler;
*/
JNIEXPORT jobjectArray JNICALL Java_model_JNIResultSet_getSpieler
(JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

And finally my C code looks like that:

JNIEXPORT jobjectArray JNICALL
JAVA_model_JNIResultSet_getSpieler(JNIEnv *env, jobject obj) {

Spieler *ptr = head;
jobjectArray ret;
int i;
jclass clazz = (*env)->FindClass(env, "model/Spieler");
jmethodID mid = (*env)->GetMethodID(env, clazz, "<init>", "(III)V");
jobject object; 

ret= (*env)->NewObjectArray(env, count,
        clazz,
        NULL);

for(i = 0; i < count; i++) {
    object = (*env)->NewObject(env, clazz, mid, ptr);
    (*env)->SetObjectArrayElement(env,
            ret, i, object);
    ptr = ptr->next;
}

return ret;
}

Do you have any suggestions how to fix that problem?
I also don't know if the C code is right, maybe that's the problem?

I execute it this way:

cd src
javac model/JNIResultSet.java
cd ..

cd bin
javah -jni model.JNIResultSet

gcc -fPIC -o libspieler.so -shared -I/usr/java/jdk1.8.0_73/include/ SharedTable.c -lc

java -Djava.library.path=/home/pupil/workspace/JNITableV2/bin/ model.JNIResultSet

Probably this is the error I've updated the C code but I think it's wrong:

jclass clazz = (*env)->FindClass(env, "model/JNIResultSet");
jmethodID mid = (*env)->GetMethodID(env, clazz, "getSpieler", "()Lmodel/Spieler;");

nm -D reports:

U atoi
0000000000202088 B bss_start
00000000002020b0 B current
w __cxa_finalize
0000000000202088 D _edata
00000000002022b8 B _end
U fclose
0000000000000ef0 T _fini
U fopen
w __gmon_start
00000000002020a8 B head
0000000000000948 T _init
0000000000000b35 T insertFirst
U _IO_getc
w _ITM_deregisterTMCloneTable
w _ITM_registerTMCloneTable
0000000000000ca2 T JAVA_model_JNIResultSet_getSpieler
w _Jv_RegisterClasses
U malloc
U memcpy
U memset
0000000000000c49 T reverse
U strcpy
00000000002020c0 B string
U strlen

Answer 1

getSpieler() method could be declared static; you can use it without instantiating JNIResultSet class.

mid should point to the constructor, not getSpieler(), but the <init> signature is wrong: it should take Ljava/lang/String;Ljava/lang/String;I and not three ints:

jmethodID mid = (*env)->GetMethodID(env, clazz, "<init>", "(Ljava/lang/String;Ljava/lang/String;I)V");
…
jobject strVorname = (*env)->NewStringUTF(env, ptr->vorname);
jobject strNachname = (*env)->NewStringUTF(env, ptr->nachname);
object = (*env)->NewObject(env, clazz, mid, strVorname, strNachname, ptr->trikotnummer);

Always check the method IDs and objects for NULL before proceeding to the next step.

Regarding the unsatisfied link, check that the libspieler.so file is good: run nm -D to see if JAVA_model_JNIResultSet_getSpieler is actually exported. rename JAVA_model_JNIResultSet_getSpieler to Java_model_JNIResultSet_getSpieler, exactly as indicated in the generated .h file.

Answer 2

It's probably a issue of PATH or LD_LIBRARY_PATH variable (on linux, not sure whats the environment key on windows). Trying add the directories to these variable, export them and run the application.

Try it in new session.