=head1 NAME

Inline::Java::Callback - Callback into Perl from Java.

=head1 SYNOPSIS

=for comment

   use Inline Java => <<'END' ;
      import org.perl.inline.java.* ;

      class Pod_caller extends InlineJavaPerlCaller { 
         public Pod_caller() throws InlineJavaException {
         }

         public String perl()
            throws InlineJavaException, InlineJavaPerlException {

            return (String)CallPerlSub("main::perl",
               new Object [] {}) ;
         }
      }
   END

   my $pc = new Pod_caller() ;
   print($pc->perl() . "\n") ; # prints perl

   sub perl {
      return "perl" ;
   }

=for comment


=head1 DESCRIPTION

C<Inline::Java::Callback> allows you to call Perl functions from Java. To 
do this you need to create an C<org.perl.inline.java.InlinePerlCaller> 
object. Here is a example of a typical use:

=for comment

   use Inline Java => <<'END' ;
      import java.util.* ;
      import org.perl.inline.java.* ;

      class Pod_regexp extends InlineJavaPerlCaller {
         public Pod_regexp() throws InlineJavaException {
         }

         public boolean match(String target, String pattern)
            throws InlineJavaException {
            try {
               String m = (String)CallPerlSub("main::regexp",
                  new Object [] {target, pattern}) ;

               if (m.equals("1")){
                  return true ;
               }
            }
            catch (InlineJavaPerlException pe){
               // $@ is in pe.GetObject()
            }

            return false ;
         }
      }
   END

   my $re = new Pod_regexp() ;
   my $match = $re->match("Inline::Java", "^Inline") ;
   print($match . "\n") ; # prints 1

   sub regexp {
      my $target = shift ;
      my $pattern = shift ;

      return ($target =~ /$pattern/) ;
   }

=for comment


=head1 CALLBACK API

Here are the various methods that one can use to call into
Perl:

=over 4

=item public Object CallPerlSub(String sub, 
Object args[], Class cast) 
throws InlineJavaException, InlineJavaPerlException
      
Calls the specified subroutine with the supplied arguments and tries
to create an object of type 'cast' with the result.

   /* Example */
   Integer sum = (Integer)CallPerlSub("main::add", new Object [] {Integer.valueOf(5), Integer.valueOf(3)}, Integer.class) ;
      
=item public Object CallPerlStaticMethod(String pkg, String method,
Object args[], Class cast)
throws InlineJavaException, InlineJavaPerlException
      
Calls the specified static package method (using the $pkg->$method()
notation) with the supplied arguments and tries to create an object 
of type 'cast' with the result.

   /* Example */
   Integer sum = (Integer)CallPerlStaticMethod("main", "add", new Object [] {Integer.valueOf(5), Integer.valueOf(3)}, Integer.class) ;

=item public Object eval(String code, Class cast) 
throws InlineJavaPerlException, InlineJavaException
      
Evaluates the given Perl code and tries to create an object
of type 'cast' with the result.

   /* Example */
   Integer sum = (Integer)eval("5 + 3", Integer.class) ;

=item public Object require(String module_or_file) 
throws InlineJavaPerlException, InlineJavaException
      
Requires the specified module/file by using a heuristic (currently,
checks whether or not the file exists) and calling Perl's C<require>
function using the appropriate construct.

   /* Example */
   require("Someting")
      
=item public Object require_file(String file) 
throws InlineJavaPerlException, InlineJavaException
      
Requires the specified file.

   /* Example */
   require_file("./my_stuff.pl") ;

=item public Object require_module(String module) 
throws InlineJavaPerlException, InlineJavaException
      
Requires the specified module.

   /* Example */
   require_module("Data::Dumper") ;

=back

Note: For all CallPerl* and eval methods, the 'cast' parameter is optional
and defaults to 'String.class'.
	
These methods can throw 2 types of exceptions: C<InlineJavaException> and
C<InlineJavaPerlException> (both of these belong to the C<org.perl.inline.java>
package). The former designates an internal C<Inline::Java> error and the 
latter indicates that the Perl callback threw an exception (die() or croak()).
The value of $@ (this can be a scalar or any valid "Inline::Java" object) can
be retrieved using the GetObject() method of the C<InlineJavaPerlException>
object (if you are certain that $@ was a Perl scalar, you can use the 
GetString() method).
   Z<>


=head1 CALLBACK CONTEXT

By default, callback are executed in scalar context. However if you want to
call certain functions in list context, you must insert "@" in front of the
function name. The result will then be passed on to Java as an Array:

=for comment

   use Inline Java => <<'END' ;
      import org.perl.inline.java.* ;

      class Pod_Context {
         static private String dummy[] = {} ;

         static public String [] get_list()
            throws InlineJavaException, InlineJavaPerlException {
            InlineJavaPerlCaller pc = new InlineJavaPerlCaller() ;
            return (String [])pc.CallPerlSub("@main::list",
                null, dummy.getClass()) ;
         }
      }
   END

   sub list {
      return ('a', 'b', 'c') ;
   }

   print(Pod_Context->get_list()->[1] . "\n") ; # prints b

=for comment

Note: When calling a Perl function that returns a list or array, you will
need to pass the Class object for the expected array type (in this case
String []). Since these Class objects are difficult to access for array 
types, the easiest way to do this is to create a dummy array of the desired 
type and call the getClass() method on that object (as seen above).
   Z<>


=head1 CALLBACK LOOPS

It is now possible to use callbacks from different Java threads. One of the 
big advantages of this is that you can now handle, for example, SWING events 
in Perl. Here's an example:

   use Inline Java => <<'END' ;
      import java.util.* ;
      import org.perl.inline.java.* ;
      import javax.swing.* ;
      import java.awt.event.* ;

      class Pod_Button extends InlineJavaPerlCaller
                       implements ActionListener {
         JFrame frame = null ;

         public Pod_Button() throws InlineJavaException {
            frame = new JFrame("Pod_Button") ;
            frame.setSize(100,100) ;
            JButton button = new JButton("Click Me!") ;
            frame.getContentPane().add(button) ;
            button.addActionListener(this) ;
            frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE) ; 
            frame.show() ;
         }

         public void actionPerformed(ActionEvent e){
            try {
               CallPerlSub("main::button_pressed", new Object [] {}) ;
            }
            catch (InlineJavaPerlException pe){
               // $@ is in pe.GetObject()
            }
            catch (InlineJavaException pe) {
               pe.printStackTrace() ;
            }
         }

         public void close(){
            frame.dispose() ;
            frame.hide() ;
            frame = null ;
         }

         public void quit(){
            System.exit(0) ;
         }
      }
   END

   my $b = new Pod_Button() ;
   $b->StartCallbackLoop() ;
   $b->close() ;

   # Maybe do some other stuff

   exit() ;      # in client-server mode, optional
   $b->quit() ;  # in JNI mode

   sub button_pressed {
      print("click!\n") ; # prints click!
      $b->StopCallbackLoop() ;
   }

The StartCallbackLoop method can be called on any 
C<org.perl.inline.java.InlineJavaPerlCaller> object and will block the 
current thread and allow the reception of callbacks through
any InlineJavaPerlCaller that has been created by the same (current) thread.
The only way to interrupt such a StartCallbackLoop method is to call the
StopCallbackLoop method on any C<org.perl.inline.java.InlineJavaPerlCaller> 
object that has been created by that same thread.

Also, only threads that communicate with Perl through C<Inline::Java> are allowed
to create C<org.perl.inline.java.InlineJavaPerlCaller> objects and invoke their 
StartCallbackLoop / StopCallbackLoop methods.
   Z<>


=head1 SELECT-STYLE CALLBACK LOOPS

The disadvantage with the type of callback loop presented in the previous 
section is that the main portion of the Perl program is completely blocked
while waiting for callbacks. In version 0.51 a new API for callback loops 
was introduced, allowing for callbacks to be processed much in the same 
fashion one uses select(2) to read data from a filehandle. Here's an 
example: 

   use Inline Java => <<'END' ;
      import java.util.* ;
      import org.perl.inline.java.* ;
      import javax.swing.* ;
      import java.awt.event.* ;

      class Pod_Button extends InlineJavaPerlCaller
                       implements ActionListener {
         JFrame frame = null ;

         public Pod_Button() throws InlineJavaException {
            frame = new JFrame("Pod_Button") ;
            frame.setSize(100,100) ;
            JButton button = new JButton("Click Me!") ;
            frame.getContentPane().add(button) ;
            button.addActionListener(this) ;
            frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE) ; 
            frame.show() ;
         }

         public void actionPerformed(ActionEvent e){
            try {
               CallPerlSub("main::button_pressed", new Object [] {}) ;
            }
            catch (InlineJavaPerlException pe){
               // $@ is in pe.GetObject()
            }
            catch (InlineJavaException pe) {
               pe.printStackTrace() ;
            }
         }

         public void close(){
            frame.dispose() ;
            frame.hide() ;
            frame = null ;
         }

         public void quit(){
            System.exit(0) ;
         }
      }
   END

   my $b = new Pod_Button() ;  
   $b->OpenCallbackStream() ;
   while ((my $rc = $b->WaitForCallback(5)) > -1){
      if ($rc > 0){
         # A callback is pending, we must process it.
         $b->ProcessNextCallback() ;
      }
      else {
         # A timeout has occurred after, in this case, 5 secs.
         print "5 seconds have passed, still waiting for callback...\n" ;
         # Maybe do some other stuff
      }
   }
   $b->close() ;

   # Maybe do some other stuff

   exit() ;      # in client-server mode, optional
   $b->quit() ;  # in JNI mode

   sub button_pressed {
      print('click!' . "\n") ; # prints click!
      $b->CloseCallbackStream() ;
   }

The StartCallbackStream method can be called on any InlineJavaPerlCaller object
to initialize a channel to receive callbacks. The WaitForCallback method can 
then be called with a float timeout value (-1 means wait forever, 0 means return 
immediately). The WaitForCallback method can return:

   rc  >  0, indicating that rc callbacks are waiting to be processed
   rc ==  0, indicating that a timeout has occurred and no callbacks are waiting
   rc == -1, indicating that the callback stream has been closed

The callback stream can be closed by calling CloseCallbackStream, which works 
similarly to the StopCallbackLoop method used in the previous section. 

Also, the restrictions regarding thread communication stated in the previous
section are valid in this case as well.
   Z<>


=head1 SEE ALSO

L<Inline::Java>, L<Inline::Java::PerlNatives>, L<Inline::Java::PerlInterpreter>.
   Z<>


=head1 AUTHOR

Patrick LeBoutillier <patl@cpan.org> is the author of Inline::Java.

Brian Ingerson <ingy@cpan.org> is the author of Inline.
   Z<>
 

=head1 COPYRIGHT

Copyright (c) 2001-2004, Patrick LeBoutillier.

All Rights Reserved. This module is free software. It may be used,
redistributed and/or modified under the terms of the Perl Artistic
License. See http://www.perl.com/perl/misc/Artistic.html for more
details.

=cut
