code in blog.sheimi.me: 2012-09-05-a-summary-of-using-jni (2)

cvjni.cpp

//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;
}