[Info-vax] Is it possible to write a JNI to give Java the VMS calling standard?

[Arne Vajhøj]

On 7/1/2015 7:52 AM, Dirk Munk wrote:
> A Java Native Interface (JNI) is a piece of software that makes it
> possible to call Java from another language, or another language from Java.
>
> As we all know, VMS has a calling standard that makes it possible to
> call routines written in another language. Java obviously doesn't have
> that, however I imagine that a VMS specific Java Native Interface could
> offer the standard calling interface?

Let us assume that Java->native is the most interesting.

For fun I tried creating a generic JNI solution that allows to
call a routine in a shareable image from Java using VMS calling
standard syntax.

This is now working:

     private static void testDefaultAccessTraditionalStyle() {
         try {
             CharacterString buf = new CharacterString(255);
             Word retlen = new Word();
             int sts = call("LIBRTL", "LIB$GET_LOGICAL", 
byDescriptor(new CharacterString("DISK2")),
                                                         byDescriptor(buf),

byReference(retlen));
             String res = createString(buf, retlen);
             System.out.println(sts + " |" + res + "|");
         } catch(Exception ex) {
             ex.printStackTrace();
         }
     }
     private static void testExplicitAccessTraditionalStyle() {
         try {
             CharacterString buf = new CharacterString(255);
             Word retlen = new Word();
             int sts = call("LIBRTL", "LIB$GET_LOGICAL", 
readOnly(byDescriptor(new CharacterString("DISK2"))),

writeOnly(byDescriptor(buf)),

writeOnly(byReference(retlen)));
             String res = createString(buf, retlen);
             System.out.println(sts + " |" + res + "|");
         } catch(Exception ex) {
             ex.printStackTrace();
         }
     }
     private static void testDefaultAccessFluentStyle() {
         try {
             CharacterString buf = new CharacterString(255);
             Word retlen = new Word();
             int sts = call("LIBRTL", "LIB$GET_LOGICAL", pass(new 
CharacterString("DISK2")).byDescriptor(),

pass(buf).byDescriptor(),

pass(retlen).byReference());
             String res = createString(buf, retlen);
             System.out.println(sts + " |" + res + "|");
         } catch(Exception ex) {
             ex.printStackTrace();
         }
     }
     private static void testExplicitAccessFluentStyle() {
         try {
             CharacterString buf = new CharacterString(255);
             Word retlen = new Word();
             int sts = call("LIBRTL", "LIB$GET_LOGICAL", pass(new 
CharacterString("DISK2")).byDescriptor().readOnly(),

pass(buf).byDescriptor().writeOnly(),

pass(retlen).byReference().writeOnly());
             String res = createString(buf, retlen);
             System.out.println(sts + " |" + res + "|");
         } catch(Exception ex) {
             ex.printStackTrace();
         }
     }

The syntax a a little bit cumbersome, but it is very
VMS-calling-standard'ish.

Drop me a note if someone want a copy.

Arne