JNI Demo (invode opencv ...)

cvjni.cpp

#include "cvjni.h"
#include <opencv2/opencv.hpp>
#include <vector>
#include <iostream>

using namespace std;
using namespace cv;

/*
 * Class:     CVJNI
 * Method:    toBMP
 * Signature: ([B)[B
 */
JNIEXPORT jbyteArray JNICALL Java_CVJNI_toBMP (JNIEnv * env, jclass jc, jbyteArray jba) {
  cout << "This is in JNI" << endl;

  //convert jbyteArray to vector<char>
  unsigned char * isCopy;
  jbyte* jbae = env->GetByteArrayElements(jba, isCopy);
  jsize len = env->GetArrayLength(jba);
  char * imageSource = (char *)jbae;
  vector<char> imageSourceV;
  for (int i = 0; i < len; i++) {
    imageSourceV.push_back(imageSource[i]);
  }

  //convert format
  Mat image = imdecode(imageSourceV, CV_LOAD_IMAGE_COLOR);
  vector<unsigned char> imageDesV;
  imencode(".bmp", image, imageDesV); 

  //convert vector<char> to jbyteArray
  jbyte* result_e = new jbyte[imageDesV.size()];
  jbyteArray result = env->NewByteArray(imageDesV.size());
  for (int i = 0; i < imageDesV.size(); i++) {
    result_e[i] = (jbyte)imageDesV[i];
  }
  env->SetByteArrayRegion(result, 0, imageDesV.size(), result_e);
  return result;
}

CVJNI.java

import java.io.*;

public class CVJNI {
  //Load jni library
  static {
    try {
      System.loadLibrary("cvjni");
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  //native method
  public static native byte[] toBMP(byte[] imageSource);

  //main
  public static void main(String [] args) {
    String input = args[0];
    String output = args[1];

    FileInputStream fi = null;
    FileOutputStream fo = null;

    try {
      File infile = new File(args[0]);
      int len = (int)infile.length();
      //get source
      fi = new FileInputStream(infile);
      byte[] imageSource = new byte[len];
      fi.read(imageSource, 0, len);
      //revoke native method
      byte[] outImage = CVJNI.toBMP(imageSource);
      //write
      fo = new FileOutputStream(output);
      fo.write(outImage);
    } catch(IOException e) {
      e.printStackTrace();
    } finally {
      try {
        if (fi != null)
          fi.close();
        if (fo != null)
          fo.close();
      } catch(IOException e) {
        e.printStackTrace();
      }
    }
  }
}

Makefile

# FOR MAC
CC=g++
SEARCH_LIB=-lopencv_core -lopencv_highgui
INCLUDE=-I/usr/local/include -I$(JAVA_INCLUDE)
LIBRARY=-L/usr/local/lib
FLAGS= -m64 -dynamiclib -fPIC
OUT=libcvjni.jnilib
SRC=cvjni.cpp

mac:
  $(CC) $(FLAGS) $(LIBRARY) $(SEARCH_LIB) $(INCLUDE) $(SRC) -o $(OUT)

# FOR LINUX

CC=g++
CV_PATH=/usr/local/lib
SEARCH_LIB=$(CV_PATH)/libopencv_core.so $(CV_PATH)/libopencv_highgui.so
INCLUDE=-I/usr/local/include -I$(JAVA_INCLUDE)
LIBRARY=-L/usr/local/lib
OUT=libcvjni.so
SRC=cvjni.cpp


FLAGS= -m64 -shared -fPIC
all:
  $(CC) $(FLAGS) $(SRC) $(SEARCH_LIB) -o $(OUT) $(INCLUDE) 

Thanks friend!!
Your code helped me to return cvMat -> byte Array from JNI.

converting JAVA byte[] into openCV mat through imread function ? is this possible or not !

the way you convert from jbyteArray to vector is too expensive, copy byte by byte