Re: Calling Java from RPG

Nick,

Barbara has already given you the key to solving the issue. This particular issue is one that comes up in Java pretty often, particularly in learning curve mode.

Java needs to find the class and the classpath is the only way. So if you have only /JavaSrc on your classpath, all class resolution will include that folder to begin with. But this isn't always clear because you may just decide to copy a class file from one directory to another and still expect it to work, just like copying an executable or batch file from one folder to another works with other programs. Java is different because it has a "package" declaration in the java source itself that it uses to resolve the class. So if your java source has a package declaration, the java class file has to be in a folder with the same structure as the package. I won't go into the details as to why this is necessary but take it as a "given" for now. There are other ways to load classes but we won't go into that either.

So if you decide to create a java program with the package name of "programs.nick.levenshtein" and create a class using that package name and the class is called MyClass, then if your classpath has /JavaSrc it in, your JavaSrc folder must also have a subfolder structure of /programs/nick/levenshtein/ and the MyClass.class file should be in it.

Invocation is also relative to that so if you were to execute the class it would be programs/nick/levenshtein/MyClass.class and if the classpath has /JavaSrc in it, it would be one of the folders that would be checked for the path/class combination that your package declaration/Class name determines. So in the invocation of programs/nick/levenshtein/MyClass.class the classpath of /JavaSrc would allow /programs/nick/levenshtein/MyClass.class to be found (remember? You compiled into /JavaSrc/programs/nick/levenshtein/MyClass.class)

So either remove any package declaration OR make sure that you have the class in a folder that is a combination of a classpath folder plus your package name (in a folder of the same structure with "/" in place of the "." in the package name)

Hope this will help a bit more.

Pete



Nick Arndt wrote:

Scott I have changed my prototype to this:
d Levenshtein pr o extproc(*java:
d 'Difference':
d *constructor)

d LD pr 10i 0 extproc(*java:
d 'Difference':
d 'LD')
d iString1 like(String1)
d iString2 like(String1)

and moved my Difference.class to a new directory '/JavaSrc', and added that
directory to my classpath.

But I am still getting a noClassDef found error.

Any Idea?

Thanks.

On Wed, Oct 29, 2008 at 12:48 PM, Scott Klement
<rpg400-l@xxxxxxxxxxxxxxxx>wrote:

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;
}
}

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