JNI java.lang.UnsatisfiedLinkError,cannot link method

Question

I have seen a lot of questions of UnsatisfiedLinkError and I know what my problem is. I get

Exception in thread "main" java.lang.UnsatisfiedLinkError: Test.initCamera(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)J

This means the dll has been loaded but it cannot find the method. However, I've checked my source code and java code. The method name and arguments are all right. I don't know what's wrong with my code.

Here are my codes.

Java:

public class Test {
public native long initCamera(String ip,String port,String username,String pwd); 
public native int snapPic(long id,String savePath,int no);
static{
    System.loadLibrary("dhconfigsdk");
    System.loadLibrary("dhnetsdk");
    System.loadLibrary("dhplay");
    System.loadLibrary("CameraCatcher");
}
public static void main(String[] args) {
    // TODO Auto-generated method stub
    Test tNative = new Test();
    String ip="192.108.1.108";
    String port="37777";
    String username="admin";
    String pwd="123456";
    long cameraId=tNative.initCamera(ip,port,username,pwd);
    System.out.println(cameraId);
    String savePath="D:/";
    int number=tNative.snapPic(cameraId,savePath,0);
}
}

C++:

JNIEXPORT jlong JNICALL Java_CameraCatcher_initCamera
(JNIEnv * env, jclass c, jstring arg_ip, jstring arg_port, jstring arg_username, jstring arg_pwd)
{
    ......
    return lLogin;
}


JNIEXPORT jint JNICALL Java_CameraCatcher_snapPic
(JNIEnv * env, jclass c, jlong arg_id, jstring arg_path, jint arg_no)
{
    .....
    return 12;
}

This really drives me crazy.

Update 1: Thanks for everyone's reply. I've changed my code just as @Mr Tarik showed.

Java:

public class CameraCatcher {
    static{
         System.loadLibrary("CameraCatcher");
    }
    public native long initCamera(String ip,String port,String username,String pwd);
    public native int snapPic(long id,String savePath,int no);
    public static void main(String[] args)
    {
        CameraCatcher tNative = new CameraCatcher();
        String ip="192.108.1.108";
        String port="37777";
        String username="admin";
        String pwd="123456";
        long cameraId=tNative.initCamera(ip,port,username,pwd);
        System.out.println(cameraId);
        String savePath="D:/project/j2ee/Example/result";
        int number=tNative.snapPic(cameraId,savePath,0);
    }
}

Then I use javah to generate header file:

#include <jni.h>

#ifndef _Included_CameraCatcher
#define _Included_CameraCatcher
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     CameraCatcher
 * Method:    initCamera
 * Signature: (Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)J
 */
JNIEXPORT jlong JNICALL Java_CameraCatcher_initCamera
  (JNIEnv *, jobject, jstring, jstring, jstring, jstring);

/*
 * Class:     CameraCatcher
 * Method:    snapPic
 * Signature: (JLjava/lang/String;I)I
 */
JNIEXPORT jint JNICALL Java_CameraCatcher_snapPic
  (JNIEnv *, jobject, jlong, jstring, jint);

#ifdef __cplusplus
}
#endif
#endif

C++ code:

JNIEXPORT jlong JNICALL Java_CameraCatcher_initCamera
(JNIEnv * env, jobject c, jstring arg_ip, jstring arg_port, jstring arg_username, jstring arg_pwd)
{
    return 1;
}
JNIEXPORT jint JNICALL Java_CameraCatcher_snapPic
(JNIEnv * env, jobject c, jlong arg_id, jstring arg_path, jint arg_no)
{
    return 2;
}

I compile this code and get new dll. However it still has the error as before.......

Update 2: Yes.It works. I don't know why the function definition code changed in my .cpp file. I just changed the jclass to jobject as EJP told me the problem yesterday.Maybe it has been changed since yesterday by chance and I didn't observe. It's all my carelessness. Thanks for everyone again.

The problem is exactly what EJP said. I generated the file with static function but make it work in a non-static way. Another problem is that I generated the class CameraCatcher while I used the class Test.

Answer 1

I tested your code. you need to edit functions names in c++ you need to have something like this

    #include "test.h"
    #include <jni.h>

JNIEXPORT jlong JNICALL Java_CameraCatcher_Test_initCamera
  (JNIEnv *env, jobject  obj, jstring ip, jstring port, jstring username, jstring pwd){

    return 1.0;
}
JNIEXPORT jint JNICALL Java_CameraCatcher_Test_snapPic
  (JNIEnv *env, jobject obj, jlong id, jstring savePath, jint no){
    return 5;
}

dont forget the name of your class Test to add it in Java_CameraCatcher_Test_snapPic.

edit 1: this is what i have in header:

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

#ifndef _Included_CameraCatcher
#define _Included_CameraCatcher
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     CameraCatcher
 * Method:    initCamera
 * Signature: (Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)J
 */
JNIEXPORT jlong JNICALL Java_CameraCatcher_initCamera
  (JNIEnv *, jobject, jstring, jstring, jstring, jstring);

/*
 * Class:     CameraCatcher
 * Method:    snapPic
 * Signature: (JLjava/lang/String;I)I
 */
JNIEXPORT jint JNICALL Java_CameraCatcher_snapPic
  (JNIEnv *, jobject, jlong, jstring, jint);

#ifdef __cplusplus
}
#endif
#endif

c++:

#include "cameracatcher.h"
#include <jni.h>
#include <stdio.h>
#include <iostream>
#include <unistd.h>
JNIEXPORT jlong JNICALL Java_CameraCatcher_initCamera
  (JNIEnv *env, jobject  obj, jstring ip, jstring port, jstring username, jstring pwd){

    return 1.0;
}
JNIEXPORT jint JNICALL Java_CameraCatcher_snapPic
  (JNIEnv *env, jobject obj, jlong id, jstring savePath, jint no){
    return 5.5;
}

Java:

public class CameraCatcher {

    public native long initCamera(String ip, String port, String username, String pwd);

    public native int snapPic(long id, String savePath, int no);

    static {
        System.load("/home/tarik/NetBeansProjects/Testc++/dist/test.so");
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        CameraCatcher tNative = new CameraCatcher();
        String ip = "192.108.1.108";
        String port = "37777";
        String username = "admin";
        String pwd = "123456";
        long cameraId = tNative.initCamera(ip, port, username, pwd);
        System.out.println(cameraId);
        String savePath = "D:/";
        int number = tNative.snapPic(cameraId, savePath, 0);
        System.out.println(number);
    }
}

All works fine.

Answer 2

The Java class that contains the native methods is named Test. But you generated the C++ header for class named CameraCatcher (in default package).

You can either rename the Java class, or change the C++ function to Java_Test_initCamera and Java_Test_snapPic. Don't forget to define these functions as extern "C" (we usually do that in header file, generated by javah).

Answer 3

THe JNI method names need to follow a convention. The method names can be generated using built-in tools that come with JDK.

Please see this link for more details. https://www3.ntu.edu.sg/home/ehchua/programming/java/JavaNativeInterface.html