JNI UnsatisfiedLinkError when running ant sample on Ubuntu

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This is a bug, could you submit a ticket to OpenCV bug tracker? And I suggest you use stable '2.4' branch, because 'master' currently contains next major version development code.

I get this error ONLY when I try to run as a groovy script, but not when I use the java classes. I use OpenCV 2.4.5 (installed via git as suggested in the intro to Java development OpenCV 2.4.5 document). Instead of using the ant build, I simply compile and then run SimpleSample.java which works fine, as in:

javac -cp ../build/bin/opencv-245.jar:. SimpleSample.java
java -cp ../build/bin/opencv-245.jar:. -Djava.library.path=../build/lib SimpleSample

My goal is to run this in groovy. I have groovy-fied SimpleSample.java as follows:

import org.opencv.core.Core
import org.opencv.core.Mat
import org.opencv.core.CvType
import org.opencv.core.Scalar

System.loadLibrary(Core.NATIVE_LIBRARY_NAME)
println("Welcome to OpenCV " + Core.VERSION)
def m = new Mat(5, 10, CvType.CV_8UC1, new Scalar(0)) 
println("OpenCV Mat: " + m)
...

I compile this with groovyc and then run it with java, which throws the exception.

groovyc -cp ../build/bin/opencv-245.jar:. TestGroovy.groovy
java -cp ../build/bin/opencv-245.jar:/usr/local/groovy/embeddable/groovy-all-2.1.4.jar:. -Djava.library.path=../build/lib TestGroovy

Welcome to OpenCV 2.4.5.0
Exception in thread "main" java.lang.UnsatisfiedLinkError: org.opencv.core.Mat.n_Mat(IIIDDDD)J

Dear guys

I got very similar problem with play framework. I posted this, http://answers.opencv.org/question/16689/jni-error-on-playframework-v211/ .

ggl, was it a classloader related problem? In my case, I hardly find a clue where should I start to solve because the other jni libraries works well but opencv doesn't.

symbol table problem with compilation or classloader related problem?

Thanks in advance..

After a bit of extra work, I got the groovy problem solved as well! For some reason the System.loadLibrary(CORE.NATIVE_LIBRARY_NAME) does not work well with Groovy.

I wrote the following (somewhat trivial) Java class:

import org.opencv.core.Core;
public class LibLoader {
  public static void load() {
    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
  }
}

Compile with:

javac -cp ../build/bin/opencv-245.jar:. LibLoader.java

In the groovy script use the static class as follows:

LibLoader.load()

I still have to pre-compile first with groovyc and then run the compiled java class. Here is the DetectFaceDemo as a groovy script:

/*
 * Detects faces in an image, draws boxes around them, and writes the results
 * to "faceDetection.png".
 */

LibLoader.load()

println("\nRunning DetectFaceDemo")

// Create a face detector from the cascade file in the resources directory.
// Note: I got rid of the getClass.getResource.getPath construction (lazy)
def faceDetector = new CascadeClassifier("resources/lbpcascade_frontalface.xml")
def image = Highgui.imread("resources/AverageMaleFace.jpg")

// Detect faces in the image.
// MatOfRect is a special container class for Rect.
def faceDetections = new MatOfRect()
faceDetector.detectMultiScale(image, faceDetections)

println(String.format("Detected %s faces", faceDetections.toArray().length))

// Draw a bounding box around each face.
for (Rect rect : faceDetections.toArray()) {
  Core.rectangle(image, new Point(rect.x, rect.y), new Point(rect.x
      + rect.width, rect.y + rect.height), new Scalar(0, 255, 0))
}

// Save the visualized detection.
def filename = "faceDetection.png"
println(String.format("Writing %s", filename))
Highgui.imwrite(filename, image)

Compile and run with:

groovyc -cp ../build/bin/opencv-245.jar:. DetectFace.groovy
java -cp ../build/bin/opencv-245.jar:/usr/local/groovy/embeddable/groovy-all-2.1.4.jar:. -Djava.library.path=../build/lib DetectFace

Results:

Running DetectFaceDemo
Detected 1 faces
Writing faceDetection.png

I reckon I will get groovy to work without the need for compilation first (there seems to be a problem with java.library.path).

What's neat about groovy is the simplicity of the code. I used to work with Java Advanced Imaging, but now that OpenCV has gpu-enabled routines, I want to go this road.