topic Re: calling C from java in Operating System - OpenVMS

calling C from java

SAMI AHMAD — Thu, 02 Apr 2009 18:50:17 GMT

I am seeing few examples here on how to call Cobol or Fortran from java but I couldnt find any document or example on how to call C from java ..can someone point me in the right direction?

thanks

Re: calling C from java

Mike Kier — Thu, 02 Apr 2009 19:13:42 GMT

Tim Sneddon from Kednos had a good article, "Calling OpenVMS native routines from Java," in the OpenVMS Technical Journal, Volume 12 (http://h71000.www7.hp.com/openvms/journal/index.html) which, although using a PLI example, should (and claims to be) extensible to C.

Re: calling C from java

Duncan Morris — Thu, 02 Apr 2009 19:16:00 GMT

Sami,

see this page:

http://h18012.www1.hp.com/java/faq/ovms.html#4.1a

Duncan

Re: calling C from java

John Gillings — Thu, 02 Apr 2009 20:38:11 GMT

SAMI,

Calling C shouldn't be any different from Cobol or Fortran. The VMS calling standard is specifically designed to make intra language calls possible, and relatively painless.

The biggest issue is matching data types between the languages. There should be a better match for data types between Java and C, as you may not need to worry about string descriptors and packed decimal types.

Start with your existing Fortran example, and replace the Fortran routine with a C equivalent. Make sure you can receive and return all the data types you're interested in.

I'd expect far more people to be calling C from Java than Cobol. Chances are, the reason you can't find any example code is it's too easy!

Re: calling C from java

Guy Peleg — Fri, 03 Apr 2009 04:40:22 GMT

Sami,

Please contact me offline and I would
be happy to provide you with few examples
that call C from Java.

Regards,

Guy Peleg
Maklee Engineering
www.maklee.com
guy.peleg@company_name.com

Re: calling C from java

SAMI AHMAD — Fri, 03 Apr 2009 16:51:48 GMT

whats your email address?

Re: calling C from java

Hoff — Fri, 03 Apr 2009 18:33:57 GMT

What is Guy's address? Since you're looking for help with the JNI and that's going to put you rather deep into the Java and C coding requirements, here is the answer to your question in the form of some C coding practice.

:-)

$ type y.c
#include
main() { printf("guy.peleg@%s.com","maklee"); return 1; }
$
$ cc y
$ link y
$ run y
[the answer appears here]
$

Re: calling C from java

SAMI AHMAD — Fri, 03 Apr 2009 21:34:30 GMT

iam willing to take the challange :)
thanks

Re: calling C from java

Jean-François Piéronne — Sat, 04 Apr 2009 13:58:53 GMT

Sami,

you can also use SWIG, which generates the jackets routines: http://www.swig.org/

SWIG 1.3.31 has been ported on OpenVMS and I have extensively used it without any problem (but not with java...)

JF

Re: calling C from java

SAMI AHMAD — Sun, 05 Apr 2009 22:38:36 GMT

based on Guy Peleg's example I am trying to put together this extern C program call, can someone point out why iam unable to compile ?
Guy thanks for your valuable example to give me a starting point.

SUNNY2$ type snd_snmp.java
class SYSTEMCALL {
public native int SNMPTRAP (String msg);
static {
System.loadLibrary("SNDSNMP_C");
}
public static void main (String[] args) {

System.out.println("This is java ..calling the C routing");
int result = new SYSTEMCALL().SNMPTRAP("TEST TRAP MSG");
System.out.println("for now lets omit this");
}
}

$ javac snd_snmp.java

$ javah -jni "SYSTEMCALL"

$TYPE SYSTEMCALL.H

/* DO NOT EDIT THIS FILE - it is machine generated */
#include
/* Header for class SYSTEMCALL */

#ifndef _Included_SYSTEMCALL
#define _Included_SYSTEMCALL
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: SYSTEMCALL
* Method: SNMPTRAP
* Signature: (Ljava/lang/String;)I
*/
JNIEXPORT jint JNICALL Java_SYSTEMCALL_SNMPTRAP
(JNIEnv *, jobject, jstring);

#ifdef __cplusplus
}
#endif
#endif

SUNNY2$ type sndsnmp_c.c
#include "SYSTEMCALL.H"
#include
#include
#include

#define size 512
static char cmdbuffer[size];

/* main(int argc, char **argv ) */

JNIEXPORT jint JNICALL Java_SYSTEMCALL_SNMPTRAP
(JNIEnv *env, jobject obj , jstring cmdbuffer) {

int i;
int sts;
char *cmd = "mcr sys$system:tcpip$snmp_trapsnd.exe 0.0 local 0 0 0 -h 10.100.18.245 -v2c 1.3.6.1.6.3.1.1.4.1.0 \"D\"";

strncat (cmdbuffer, cmd,size);
strncat (cmdbuffer, " \"",size);
strncat (cmdbuffer, argv[1],size);
strncat (cmdbuffer,"\"",size);
printf ("%s\n",cmdbuffer);
sts = system(cmdbuffer);
printf( " sts = %%x%08x.\n", sts);
}
SUNNY2$

SUNNY2$ cc /prefix=all/float=ieee/ieee=denorm/defin=JIT_OPTION/names=(short,as_is)
/reent=multithread/includ=SYS$COMMON:[JAVA$142.INCLUDE...] SNDSNMP_C

SUNNY2$ cc /prefix=all/float=ieee/ieee=denorm/defin=JIT_OPTION/names=(short,as_is) /reent=multithread/includ=SYS$COMMON:[JAVA$142.
INCLUDE...] SNDSNMP_C

strncat (cmdbuffer, cmd,size);
.............^
%CC-W-PTRMISMATCH, In this statement, the referenced type of the pointer value "cmdbuffer" is "struct _jobject", which is not compat
ible with "char".
at line number 18 in file DISK$ORACLE:[ORACLE9I]SNDSNMP_C.C;18

Re: calling C from java

Dennis Handly — Mon, 06 Apr 2009 03:38:29 GMT

>can someone point out why I am unable to compile?

You have:
static char cmdbuffer[size];
JNIEXPORT jint JNICALL Java_SYSTEMCALL_SNMPTRAP
(JNIEnv *env, jobject obj, jstring cmdbuffer) {

Your parm name cmdbuffer hides your file scope definition.

If you were using a real language like C++, you could just use ::cmdbuffer to access the global scope. :-)

Re: calling C from java

Martin Vorlaender — Mon, 06 Apr 2009 05:15:01 GMT

Apart from cmdbuffer used twice, jstring is NOT an ordinary C char*. You'll have to convert the jstring parameter - see http://java.sun.com/docs/books/jni/html/objtypes.html#4001 , especially the methods GetStringChars and GetStringLength.

cu,
Martin

Re: calling C from java

x2084 — Mon, 06 Apr 2009 06:58:39 GMT

After learning C or a "real" languages and how to call their functions from Java in order to do a system() with a C-style string retrieved from a Java and/or C++ string class, you may want to learn what the Runtime class can do for you.

Re: calling C from java

SAMI AHMAD — Mon, 06 Apr 2009 14:49:43 GMT

ok I am not getting compiler errors now after i made the following change but iam now not able to run it using java

static char cmdbuffer[size];

/* main(int argc, char **argv ) */

JNIEXPORT jint JNICALL Java_SYSTEMCALL_SNMPTRAP
(JNIEnv *env, jobject obj , jstring msg) {

int i;
int sts;
char *cmd = "mcr sys$system:tcpip$snmp_trapsnd.exe 0.0 local 0 0 0 -h 10.100.18.245 -v2c 1.3.6.1.6.3.1.1.4.1.0 \"D\"";

char buf[512];
const jbyte *str;
str = (*env)->GetStringUTFChars(env, msg, NULL);
if (str == NULL) {
return NULL; /* OutOfMemoryError already thrown */
}
printf("%s", str);
(*env)->ReleaseStringUTFChars(env, msg, str);

/* strncat (cmdbuffer, cmd,size);
strncat (cmdbuffer, " \"",size);
strncat (cmdbuffer, argv[1],size);
strncat (cmdbuffer,"\"",size);
printf ("%s\n",cmdbuffer);
sts = system(cmdbuffer);
printf( " sts = %%x%08x.\n", sts);
*/
return 0;
}

$link/share=sndsnmp_c sndsnmp_c,sndsnmp_c/opt

$ JAVA "SYSTEMCALL" "testing"
Warning: JIT compiler "SUNCOMPILER" not found. Will use interpreter.
Exception in thread "main" java.lang.UnsatisfiedLinkError: no SNDSNMP_C in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1578)
at java.lang.Runtime.loadLibrary0(Runtime.java:788)
at java.lang.System.loadLibrary(System.java:834)

Re: calling C from java

SAMI AHMAD — Mon, 06 Apr 2009 14:52:12 GMT

and my options file looks like this :

SUNNY2$ type sndsnmp_c.opt
case_sensitive=YES
symbol_vector=(Java_SYSTEMCALL_SNMPTRAP=PROCEDURE)
case_sensitive=NO
java$java_shr/share
gsmatch=lequal,1,1

Re: calling C from java

SAMI AHMAD — Mon, 06 Apr 2009 15:03:43 GMT

looking at the files in sys$common:[java$142.vms_demo...]build_example.com , I see following which is confusing me, what
is the function of the libgesyi logical pointing to the shared image ? I didnt define any such logical, is this the reason iam getting error? how is this logical name constructed ?

$ link/share=getjpi_shr.exe getjpi_nat.obj,getjpi.opt/opt,java.opt/opt
$ link/debug/share=getjpi_g_shr.exe getjpi_nat.obj,getjpi.opt/opt,java_g.opt/opt
$
$ define/nolog libgetsyi sys$disk:[]getsyi_shr.exe
$ define/nolog libgetsyi_g sys$disk:[]getsyi_g_shr.exe
$

Re: calling C from java

SAMI AHMAD — Mon, 06 Apr 2009 15:22:56 GMT

ok I found on HP site how to link the image properly and that fixed the issue so now i can concentrate on application errors , any ideas why iam getting those special characters instead of the string that iam inputting as parameter?

SUNNY2$ link/share/exec=java$sndsnmp_c_shr.exe sndsnmp_c,sndsnmp_c/opt

SUNNY2$ def/job/log java$sndsnmp_c_shr sys$login:java$sndsnmp_c_shr.exe
SUNNY2$ JAVA "SYSTEMCALL" "TESTING"
Warning: JIT compiler "SUNCOMPILER" not found. Will use interpreter.
This is java ..calling the C routing
@Â²UPÂ²UÃ `Uî¤»U0lÅ¸z;lÅ¸zî¤»6for now lets omit this

Re: calling C from java

Martin Vorlaender — Mon, 06 Apr 2009 15:57:27 GMT

>>>
any ideas why iam getting those special characters instead of the string that iam inputting as parameter?
<<<

Because you're not using it?

- The jstring parameter msg is probably not UTF8 encoded. That's why I suggested GetStringChars and not GetStringUTFChars.
- The jbyte variable str is not a null-terminated C string. That's why I suggested using GetStringLength

cu,
Martin

Re: calling C from java

Hoff — Mon, 06 Apr 2009 16:07:15 GMT

There are Java SNMP libraries widely available that can send SNMP traps, and various of which would seem more supportable than this current approach.

Re: calling C from java

SAMI AHMAD — Mon, 06 Apr 2009 16:08:38 GMT

sorry i think the code is not upto date . iam using jstring n not jbyte

jstring jstr;
jstr = (*env)->NewStringUTF(env, result);
if (jstr == NULL) {
fprintf(stderr, "out of memory");
return 0;
}

printf("%s","now in C routine");
printf("%s", jstr);