如何直接使用jni将字节数组从c复制到java byte []属性

Question

I am writing a C module with jni for android.
my java class is

public class Payment {
    private static Payment payment = null;
    private long nativeObj;
    private byte[] sendBuffer;
    private byte[] recvBuffer;
    private byte[] msg;

    private Payment() {
        this.sendBuffer = new byte[1024];
        this.recvBuffer = new byte[1024];
        this.msg = new byte[1024];
    }

    public native void setArray();

 }

i want to fill byte arrays of Payment instance in c and i can not do it.
what is the procedure of jni call for this purpose?

i get the field id of sendBuffer with

jclass thisClass = (*env)->GetObjectClass(env, obj);
jfieldID sendId = (*env)->GetFieldID(env, thisClass, "sendBuffer", "[B");

but i can not figure out how to copy data from char[1024] to sendBuffer.

Answer 1

You can use something like this to copy data from C to java bytes array;

jint_Java_com_stack_overflow_copyBytes(JNIEnv *e, jclass obj, jlong p)
{
    jclass thisClass = (*env)->GetObjectClass(e, obj);
    jfieldID sendId = (*env)->GetFieldID(e, thisClass, "sendBuffer", "[B");        
    jbyteArray bytes = (*e)->GetObjectField(e, obj, sendId)

    jbyte* b = (*e)->GetByteArrayElements(e, bytes, NULL);
    memcpy(myCBytes, b, len);
    (*e)->ReleaseByteArrayElements(e, bytes, b, 0);
}