Re: Calling Java from C and back?

From:

"Mike Schilling" <mscottschilling@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 24 Jul 2009 14:01:28 -0700

Message-ID:

<h4d7s3$j15$1@news.eternal-september.org>

Elena wrote:

On 24 Lug, 17:49, "Mike Schilling" <mscottschill...@hotmail.com>
wrote:

Elena wrote:

Hi,

I've developed a native application which calls Java by means of JNI
and everything is going fine. What I'd like to do now is collecting
debug logs from the Java side together with logs from the main
native
application. That is, I have to call C from Java.

It doesn't seem that Java allows simple callbacks from Java to C.
The
lame solution I'm going to employ if I fail in finding a simpler
solution is to build a JNI DLL which stores C callbacks in some
Jglobal
variable and then gets loaded from Java, therefore being able to
call
those C callbacks.

Any suggestion?

Why not model the C callbacks as (native) methods on a Java class,
and use JNI the usual way?

Because I'm calling Java from an executable, just to accomplish a
task.

Right; I mean the calls from Java back to C. Is the issue that the
callbacks are located in the executable, where your JNI DLL will have a hard
time seeing them? If so, you can set an array of function pointers in the
DLL (at runtime, from your C main()), and let the native methods call them.
You can even throw Java exceptions from the native methods if the function
pointer array hasn't been set.