Re: Calling Java from RPG

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

Hi Nick,

/QIBM/UserData/Java400/ext is the Java "extensions" directory.  It's 
supposed to be used for extensions to the Java language, not for your 
own code.

It's not the "default directory of your CLASSPATH" because it's not part 
of your CLASSPATH.  Indeed, the files in that directory are loaded 
before the CLASSPATH is even considered.

One of the biggest problems with using the extensions directory is that 
any code in that directory is loaded automatically for every Java 
program.  That means you can never have two versions (such as test & 
production versions) running on the same system, because the stuff in 
the ext directory is *always* loaded first.

My recommendation is that you remove it from the ext directory. 
Instead, create your own directory.  Maybe with something like this:

CRTDIR ('/java')
CRTDIR ('/java/publicclasses')

Put all of your classes you want to be available to everyone into that 
directory, and then set the CLASSPATH envvar to point to that directory.

ADDENVVAR ENVVAR(CLASSPATH) VALUE('/java/publicclasses')

That's just a suggestion though.  The reason your example doesn't work 
is that it's expecting the Difference class to be in a subdirectory 
named "levenshtein".  So for every directory in yoru CLASSPATH, it's 
looking for a subdirectory named levenshtein that contains a Difference 
class.

In the above example, if the CLASSPATH is /java/publicclasses then your 
code is looking for a file in the IFS named 
/java/publicclasses/levenshtein/Difference.class -- because of the way 
you coded it, it's looking for a levenshtein/Difference.class in all of 
your CLASSPATH directories.


Nick Arndt wrote:
> Hi all I have a need to call a java program from RPG.  Here is my
> prototypes:
>
>      d Levenshtein     pr              o   extproc(*java:
>      d                                             'levenshtein.Difference':
>      d                                             *constructor)
>
>      d LD              pr            10i 0  extproc(*java:
>      d
> 'levenshtein.Difference':
>      d                                              'LD')
>      d iString1                            like(String1)
>      d iString2                            like(String1)
>      d Class           s               o   class(*java:
>      d                                     'levenshtein.Difference')
>      d String1         s               o   CLASS(*JAVA:'java.lang.String')
>
>       /free
>
>        // constructor for java class
>          Class = Levenshtein();
>
> When I try to call the above constructor I get an RNX0301 NoClassDefFound
>
> Here is my java program:
> The Program is in a Jar file located in QIBM\UserData\Java400\ext
> Is this the default directory for the classpath var or do i have to change
> it to look here?
>
> package levenshtein;
>
>
> public class Difference {
>     //*****************************
>     // Compute Levenshtein distance
>     //*****************************
>
>       public int LD (String s, String t) {
>       int d[][]; // matrix
>       int n; // length of s
>       int m; // length of t
>       int i; // iterates through s
>       int j; // iterates through t
>       char s_i; // ith character of s
>       char t_j; // jth character of t
>       int cost; // cost
>
>     // Step 1
>
>         n = s.length ();
>         m = t.length ();
>         if (n == 0) {
>           return m;
>         }
>         if (m == 0) {
>           return n;
>         }
>         d = new int[n+1][m+1];
>
>         // Step 2
>
>         for (i = 0; i <= n; i++) {
>           d[i][0] = i;
>         }
>             for (j = 0; j <= m; j++) {
>           d[0][j] = j;
>         }
>             // Step 3
>             for (i = 1; i <= n; i++) {
>               s_i = s.charAt (i - 1);
>               // Step 4
>               for (j = 1; j <= m; j++) {
>                 t_j = t.charAt (j - 1);
>
>                 // Step 5
>
>                 if (s_i == t_j) {
>                     cost = 0;
>                 }
>                 else {
>                     cost = 1;
>                 }
>                 // Step 6
>
>                 d[i][j] = Minimum (d[i-1][j]+1, d[i][j-1]+1, d[i-1][j-1] +
> cost);
>
>               }
>
>             }
>
>             // Step 7
>
>             return d[n][m];
>
>           }
>
>
>             // get minimum of three values
>     private int Minimum (int a, int b, int c) {
>       int mi;
>
>       mi = a;
>       if (b < mi) {
>         mi = b;
>       }
>       if (c < mi) {
>         mi = c;
>       }
>       return mi;
>     }
> }