Return list<unsigned char*> from C++ to Java using JNI

Question

I have the following JNI method,

JNIEXPORT jobject JNICALL Java_projlib_DeserializeBuffer
(JNIEnv *env, jobject obj, jbyteArray inBufferData)

I have created a list of unsigned char* and filling it using some data extracted from the inBufferData in my C++ code

list<unsigned char*> returnBuffer

I want to return the returnBuffer to my Java code, where it will be a List of byte array, List<byte[]> .

Please tell me how to pass the list of unsigned char* via a jobject through JNI and then get it in Java for further processing.

Answer 1

You will not be able to do that directly. You will have to instantiate an instance of the needed Java list implementation (since List is an interface) in C++, put it in a jobject and then add jbytearray items to it from your list and then return the list.

EXAMPLE

Since I do not have a working JNI environment, this snippet is only illustrational (feel free to edit it when you get it working), but what you need could be achieved by this:

jclass arrayListClass = env->FindClass("java/util/ArrayList"); // Find ArrayList class
jmethodID constructor = env->GetMethodID(arrayListClass, "<init>", "()V"); // Find ArrayList constructor
jobject arrayList = env->NewObject(arrayListClass, constructor); // Create new ArrayList instance
jmethodID add = env->GetMethodID(arrayListClass, "add", "(Ljava/lang/Object;)Z"); // Find the ArrayList::add method
jbyteArray item =env->NewByteArray(10); // Instantiate a new byte[]
env->CallBooleanMethod(arrayList, add, item); // Add the byte[] to the ArrayList