Get the pointer of a Java ByteBuffer though JNI

Question

How can I get a pointer to the inner array of a Java ByteBuffer?

JNIEXPORT void JNICALL test(JNIEnv *env, jobject thiso) {
    jclass cls = env->FindClass("java/nio/ByteBuffer");
    jmethodID aloc = env->GetStaticMethodID(cls, "allocateDirect", "(I)Ljava/nio/ByteBuffer;");
    jobject obj = env->CallStaticObjectMethod(cls, aloc, 1000);
}

PS: I'm doing that to share the memory used by Java and C++.

Could you clarify what you're asking? If you need to return 2 things then return a struct. — Pubby, Nov 03 '11 at 19:16
Does `m_buffer` already point to allocated memory? If so, why do you say `new`? — Kerrek SB, Nov 03 '11 at 19:19

score 13 · Accepted Answer · answered Nov 03 '11 at 21:37

13

void * data = env->GetDirectBufferAddress(obj);

The ByteBuffer must be a direct one for this to work.

answered Nov 03 '11 at 21:37

Alan Stokes

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This is exactly what I need. Thank you! – Marcos Vasconcelos Nov 04 '11 at 13:05
I think `Byte* data = env->GetDirectBufferAddress(obj);` would be more descriptive. – Patrick Jan 21 '14 at 22:20

score 0 · Answer 2 · answered Nov 03 '11 at 19:16

0

If you're trying to return the address of the first element within m_buffer, then you can just do:

return m_buffer;

..or:

return &m_buffer[0]

answered Nov 03 '11 at 19:16

John Dibling

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Get the pointer of a Java ByteBuffer though JNI

2 Answers2

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