JNI - native method with ByteBuffer parameter

Question

I've got a method:

public native void doSomething(ByteBuffer in, ByteBuffer out);

Generated by javah C/C++ header of this method is:

JNIEXPORT void JNICALL Java__MyClass_doSomething (JNIEnv *, jobject, jobject, jobject, jint, jint);

How can I get a data array from jobject (that is a ByteBuffer instance) ?

score 33 · Accepted Answer · edited Mar 01 '19 at 06:26

33

Assuming you allocated the ByteBuffer using ByteBuffer.allocateDirect() you can use GetDirectBufferAddress

jbyte* bbuf_in;  jbyte* bbuf_out;

bbuf_in = (*env)->GetDirectBufferAddress(env, buf1);  
bbuf_out= (*env)->GetDirectBufferAddress(env, buf2);

edited Mar 01 '19 at 06:26

Matt

answered Apr 20 '10 at 09:27

stacker

1

The return type of GetDirectBufferAddress is void*, you need to cast it to a jbyte*: bbuf_in = (jbyte*)(env*)->GetDirectBufferAddress(env, buf1); //C bbuf_in = (jbyte*)env->GetDirectBufferAddress(buf1); //c++ – Error 454 Jun 21 '11 at 20:30
3

@Error454 This is C, you don't need to cast `void*`s – Michael Mrozek Jul 08 '15 at 17:47
1

You do need to cast if you have -Wpedantic – James Cape Jul 27 '17 at 19:12

1 Answers1