JNI in C++ to read file to jbyteArray

Question

I am writing a C++ program in UNIX to generate a shared library which will be called in java using JNI. This C++ program has to read a file in UNIX box then it will have to

Answer 1

You don't appear to be setting any byte data to the array. In fact as a jbyte is typedef'd to a char you can directly set your char array in setByteArrayRegion as follows:

env->SetByteArrayRegion( result, 0, 100, ret );

Edit: Also, assuming that the al[i] should be a1[i] you are doing something very dangerous as you are not allocating space for a1. Basically doing as I suggest above means you can get rid of that entire loop. Also don't forget to delete the C++ Array when you have finished with it (ie copied it into the jByteArray)!

JNIEXPORT jbyteArray JNICALL Java_com_sp_dll_NativeMethods_getFile
       (JNIEnv *env, jobject obj)
{
        ifstream fl("/home/rkannan/myFile.txt");
        fl.seekg(0, ios::end );
        size_t len = fl.tellg();
        char *ret = new char[len];
        fl.seekg(0, ios::beg);
        fl.read(ret, len);
        fl.close();

        jbyteArray result = env->NewByteArray( len);
        env->SetByteArrayRegion( result, 0, len, (const jbyte*)ret );

        delete[] ret;

        return result;
}