Android, generate jni Header Files with javah , show error that can't find org.opencv.core.Mat

Question

I just have an annoying problem with jni when i compile the native method in java class with javah to generate JNI header files.

If the class has used 3rd-party package, For example: org.opencv.core.Mat, then the javah will show the error that can't find the org.opencv.core.Mat class.

The OpenCV sample code as below:

package org.opencv.samples.fd;

import org.opencv.core.Mat;
import org.opencv.core.MatOfRect;

public class DetectionBasedTracker
{
public DetectionBasedTracker(String cascadeName, int minFaceSize) {
    mNativeObj = nativeCreateObject(cascadeName, minFaceSize);
}

public void start() {
    nativeStart(mNativeObj);
}

public void stop() {
    nativeStop(mNativeObj);
}

public void setMinFaceSize(int size) {
    nativeSetFaceSize(mNativeObj, size);
}

public void detect(Mat imageGray, MatOfRect faces) {
    nativeDetect(mNativeObj, imageGray.getNativeObjAddr(), faces.getNativeObjAddr());
}

public void release() {
    nativeDestroyObject(mNativeObj);
    mNativeObj = 0;
}

private long mNativeObj = 0;

private static native long nativeCreateObject(String cascadeName, int minFaceSize);
private static native void nativeDestroyObject(long thiz);
private static native void nativeStart(long thiz);
private static native void nativeStop(long thiz);
private static native void nativeSetFaceSize(long thiz, int size);
private static native void nativeDetect(long thiz, long inputImage, long faces);
}

First, I used the command

javah -classpath bin/classes -bootclasspath (the directory of android.jar) -d jni (packageName + ClassName) , shows the error "can't find the org.opencv.core.Mat

Then I modified the command to

javah - classpath bin/classes - bootclasspath (the dir of android.jar) ; (the dir of the opencv lib jar)  -d jni ..." ", this time it shows error

Exception

Exception in thread "main" java.lang.IllegalArgumentException: Not a valid class
 name: E:\Computer_Language\Java\soft_android\OpenCV-2.4.3-rc-android-sdk\OpenCV
-2.4.3-rc-android-sdk\sdk\java\bin\opencv library - 2.4.3.jar
    at com.sun.tools.javac.api.JavacTool.getTask(JavacTool.java:177)
    at com.sun.tools.javac.api.JavacTool.getTask(JavacTool.java:68)
    at com.sun.tools.javah.JavahTask.run(JavahTask.java:509)
    at com.sun.tools.javah.JavahTask.run(JavahTask.java:335)
    at com.sun.tools.javah.Main.main(Main.java:46)

I think, adding the directory of opencv lib in -bootclasspath is useful and neccessary. The error is because i just added two path in -bootclasspath or the format is something wrong?

Really confused. Please give some help , thank u!

Answer 1

This is what I did:

1.Open Command line, type to the (project)/bin/classes: 2.type: javah -classpath (opencv4android sdk path)/java/bin/classes:(your project location)/bin/classes -jni (your java class file that contains the native library interfaces)

In my project. I did:

javah -classpath /home/zijun/Dev/adt/OpencvAndroid/sdk/java/bin/classes:/home/zijun/workspace/LocTM/bin/classes -jni com.brainport.loctm.TMatching

That works on Linux Ubuntu 12.04.02 64bit OS

Answer 2

I encountered the same problem too,it cost me half day.I just copy DetectionBasedTracker.java to my poject.I use Android Studio.When I use ExternalTools>javah to generate .h files,the console print cant find org.opencv.core.Mat.copying mat.java & matofRect.java to the directory DetectionBasedTracker.java exists just cause more java class cant be find.finally,I find this problem was caused by the import * clause in java file.and we seldom use java class in native method we defined.so I cut these java method and got this:

package cn.ntu.tonguefur.nativemethod;
public class DetectionBasedTracker{
private static native long nativeCreateObject(String cascadeName,int minFaceSize);
//Other native methods
private static native void nativeDetect(long thiz,long inputImage,long faces);
}

Now you can freely use javah command to generate .h file.After that,add java methods and import packages you need.