The day I discovered Inline::Java I was very happy. Now for some of these Java projects I am working on I can reuse the code I wrote in Java from Perl. Hmmm.. was this what they meant by "write once run everywhere?" Probably not, but hey!

Here's something I ran into. I have some Java classes that are implemented as singletons. Mostly to do with database access and persisted objects. These classes follow the following pattern:

package com.schooner.test;
 
public class JumpClass {
    private static JumpClass instance = null;
 
 
    private JumpClass(){
    }
 
    public static synchronized JumpClass getInstance(){
        if ( instance == null ) {
            instance = new JumpClass();
        }
 
        return instance;
    }
 
}
[download]

For those that don't know what singleton behavior is I can sum it up by saying that a singleton gets created once and does not get re-instatiated so you have exactly one copy of it in memory.

So, now I want to access it from Perl. From Java I would do something like:

import com.schooner.test.JumpClass;

    | 
    |   Waving of hands....
    |
    JumpClass j = JumpClass.getInstance();
    | 
    |
[download]

and in doing so j now points to the one and only instance of JumpClass in memory and I can do stuff with it. Pretty handy when you want to open a connection to a database and not open too many handles to it from the same application.

So now I try and do the analog of that from Perl. Here's what I'm talking about:

#!/usr/bin/perl -w
use strict;
use Data::Dumper;
 
use Inline (
            Java => 'STUDY',
            STUDY => [ qw / com.schooner.test.JumpClass / ],
            AUTOSTUDY => 1,
            CLASSPATH=> '.'
            );
 
 
my $jc = JumpClass::getInstance();
[download]

Right? WRONG!

When I attempt to run that I get:

Undefined subroutine &JumpClass::GetInstance called at jtest.pl line 4
+2.
[download]

Huh? It is so!

So I decide to get clever and I do the following:

my $jc=main::com::schooner::test::JumpClass::getInstance();
[download]

That should work... right? WRONG! That yeilds:

Can't call method "__validate_prototype" on an undefined value at (eva
+l 11) line 45.
[download]

OK... what is a defrocked Saint of a Perl guy supposed to do?

Another bit of cleverness, but it is ugly in my opinion....

#!/usr/bin/perl -w
use strict;
use Data::Dumper;
 
use Inline (
            Java => 'STUDY',
            STUDY => [ qw / com.schooner.test.JumpClass / ],
            AUTOSTUDY => 1,
            CLASSPATH=> '.'
            );
 
 
 
    use Inline (
                Java => qq(
import com.schooner.test.JumpClass;
 
public class SingletonWrapper {
    public SingletonWrapper(){}
 
    public JumpClass getInstance(){
        JumpClass j = JumpClass.getInstance();
        return j;
    }
}
                           ),
                CLASSPATH => "."
                );
 
 
 
 
my $jc =(new SingletonWrapper())->getInstance();
 
 
 
 
 
# print Dumper($jc);
#my $jc=main::com::schooner::test::JumpClass::getInstance();
print Dumper($jc);
[download]

That worked! Here's the result:

$VAR1 = bless( {}, 'main::com::schooner::test::JumpClass' );
[download]

OK: So what is the right way to do this? Is this a bug? Is this a feature? Why can't I access the singleton (or other public methods/values) directly?

Thoughts?

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