NAME
    Java - Perl extension for accessing a JVM remotely or locally

SYNOPSIS
      use Java;
      $java = new Java;
      $frame = $java->create_object("java.awt.Frame","Frame's Title");
      $frame->setSize(400,400);
      $frame->show();
      $java->do_event($frame,"addWindowListener",\&event_handler);
  
      $array = $java->create_array("java.lang.String",5);
      // Set array element 3 to "Java is lame"
      $array->[3] = "Java is lame";
      $element_value = $array->[3]->get_value();

      $button = $java->create_object("java.awt.Button","Push Me");
      // Listen for 'Action' events from $button object
      $java->do_event($button,"addActionListener",\&event_handler);

      // Loop & wait mode
      while(1)
      {
           my $continue = $java->go;
           last if (!defined $continue);
      }

      // Got an event!
      sub event_handler
      {
            my($object_that_caused_event,$event_object) = @_;
            if ($object_that_caused_event->same($button))
            {
                    // From $button!
                    print "You pushed my button!!\n";
            }
      }

DESCRIPTION
    This module allows you to talk to a JVM on a local or remote machine.
    You can create objects, call functions, access fields, deal with arrays,
    get events & all the nonsense you can do in Java - from Perl!

Starting a JVM server
    First you must run 'JavaServer' on the machine to which you will make
    connections. Simply do a 'java JavaServer' to start the server. By
    default it will start listening on port 2000. Make sure the
    'JavaServer.jar' is in your classpath - also make sure the Swing stuff
    (JFC if you prefer) is in your classpath as well if you want to use
    Swing stuff (note this does not apply to JVM 1.2+).

Creating the root Java object
    You connect to a remote (or local) JVM when you create a new Java
    instance. The new call accepts a hash with the following keys:

            host => hostname of remote machine to connect to
                            default is 'localhost'
            port => port the JVM is listening on (JavaServer)
                            default is 2000
            event_port => port that the remote JVM will send events to
                            default is 2001.  If you specify '-1' for this
                            value then the event service will be turned off -
                            if you're not doing any GUI work this might be
                            a good idea as the second event port will NOT
                            get used/opened saving some system resources.
            authfile => The path to a file whose first line is used as a 
                            shared 'secret' which will be passed to 
                            JavaServer.  To use this feature you must start 
                            JavaServer with the '--authfile=<filename>' 
                            command-line option.
                            If the secret words match access will be granted
                            to this client.  By default there is no shared
                            secret.  See the 'Authorization' section below.
            use_old_style_arrays => tell Java.pm to use 'old-style' arrays
                            which you should NOT be using unless you need
                            backwards compatibility with 3.x Java.pm & 
                            earlier.  By default all arrays returned by 
                            JavaServer are 'tied' to the JavaArray class for 
                            easier perl-like manipulation.  See the 'Arrays' 
                            section futher down for more info.

    For example:

            $java = new Java(host => "java.zzo.com", event_port => 4032);

            # No events!
            $java2 = new Java(port => 8032, event_port => -1);

    You can have any number of java 'environments' in a Perl program.

    Also if you 'use strict' you must do a 'no struct 'subs'' 'cuz all Java
    method calls are AUTOLOAD'ed - sorry.

Creating java primitives
    The Java.pm module will treat all integers encountered in parameter
    lists as integer and strings as java Strings. All other primitive types
    must be suffixed with an identifier so Java.pm knows what primitive Java
    type to convert it to - for instance boolean types are tagged like:
    "true:b" or "false:b"

    Here's a complete list of supported Java primitives:

            Perl String Value  -> (converted to) -> Java Primitive
            -----------------                       --------------
            2344                                    int
            "23:short"                              short
            "23:byte"                               byte
            "a:char"                                char
            "23445:long"                            long
            "3.42:float"                            float
            "3.14159:double"                        double
            "true:b" or "false:b"                   boolean
            "Anything else"                         String
                    or
            "Anything else:string"                  String

    So... if you need to use an integer as a String say "343:string".

Localization and String encoding
    Quick note on String encodings, you can specify that your strings are
    encoded in a specific format using the ":string_<ENCODING>" syntax like:

            my $label = $java->create_object("java.awt.Label","Label:string_UTF8");

    This specifies that this String uses Unicode encoding. See
    http://www.javasoft.com/products/jdk/1.1/docs/guide/intl/encoding.doc.ht
    ml for the complete list of valid Java String encodings.

Creating java objects
    Once you've connected to a JVM via the 'new Java' call you can start
    creating Java objects. This is accomplished via the 'create_object'
    function. The first argument must be the 'fully-qualified'/'full path'
    of the Java object you want to create - like 'java.lang.String' or
    'java.awt.Frame'. The remaining arguments are passed to that object's
    constructor.

    For example:

            my $frame = $java->create_object("java.awt.Frame","Frame Title");
            my $dialog = $java->create_object("java.awt.Dialog",$frame,
                            "Dialog Title","true:b");

    Note the use of "true:b" in the constructor to tell Java.pm that that
    value should be a 'true' Java boolean value.

    In these cases a 'java.awt.Frame' takes a String as the lone parameter,
    whereas a 'java.awt.Dialog' takes a Frame, a String, and a boolean value
    in its constructor.

Calling java methods
    You can make both static and instantiated method calls on java objects.
    The parameter lists work exactly like constructor parameter lists - if
    you want to pass a java primitive anything other than integers or
    Strings need to be tagged accordingly. All function calls that return
    something return a java object - so even if the java function returns an
    'int' it is returned to perl as a 'java.lang.Integer'. To get the value
    of that Integer you must use the 'get_value' function. The syntax is
    exactly what you'd expect (I hope!).

    For example:

            $frame->setSize(200, 500);
            $frame->show();  # (or $frame->show)

    Note functions that don't take any parameters don't need the
    parentheses! Alternatively you can use the 'call' function to make
    method calls:

            $frame->call('setSize', 500, 500);
            $frame->call('show');

    But that's no fun!

    To call static functions the syntax is slightly different.

    For example:

    To call the static method 'forName' in the object 'java.lang.Class' it
    looks like this:

            my $class = $java->java_lang_Class("forName", "Test");

    Note you use the '$java' object returned from the call to 'new Java' to
    access static methods - the static object must be fully-qualified
    separated by '_'s instead of '.'s WHEN USED AS A FUNCTION NAME (as
    opposed to the method below when it's used as a string - in the below
    case DO NOT replace '.'s with '_'s)! And finally the first parameter is
    the name of the static function followed by any parameters to it.

    If your static class is NOT in a package you MUST use the 'static_call'
    function like:

            my $return_value = $java->static_call("MyStaticClass","<function_name>",@params);

    Even if your class is in a package you can use the 'static_call'
    function (Note when using the 'static_call' function your fully
    qualified class name is separated by '.' NOT '_'s as in the example
    above):

        my $class = $java->static_call("java.lang.Class", "forName", "Test");
            IS EXACTLY EQUIVALENT TO
            my $class = $java->java_lang_Class("forName", "Test");

    Note the use of '.'s in the first case and '_'s in the second case. Also
    the returned value '$class' in an OBJECT NOT a string. To 'stringify' it
    use the 'get_value' function as described below. Here's a sneak peek:

        print "This java.lang.Class object's name is ", $class->get_value, "\n";

Getting and Setting java object fields
    You can get and set individual fields in java objects (static or
    instantiated) using the 'get_field' and 'set_field' methods. All
    'get_field' calls return java objects just like calling java functions.
    You must use the 'get_value' function to 'unwrap' primitive types to
    their actual values.

    For example:

    Get a static field

            my $win_act = $java->get_field("java.awt.event.WindowEvent",
                                                    "WINDOW_ACTIVATED");

    Note the first parameter must be the fully qualified java object name
    and the second parameter is the static field.

    Get an instantiated field

            my $obj = $java->create_object("java.my.Object");
            my $field = $obj->get_field("my_field");

    Similarly to set a field another parameter is added to the 'set_field'
    call with the object that the specified field is to be set to:

    Set a static field

            $java->set_field("java.static.Object","field_name",$obj);

    Set an instantiated field

            $obj->set_field("integer_field_name",400);

Getting values
    To 'unwrap' java primitives (including Strings) you need to call the
    'get_value' function. This will stringify any object given to it -
    typcially this is only useful for 'unwrapping' java primitives and
    Strings. Note for all other object the 'toString()' method is called.

    For example:

            my $string1 = $java->create_object("java.lang.String","Mark");
            my $string2 = $java->create_object("java.lang.String","Jim");

            if ($string1 eq $string2)
            {
                    # WRONG!!!  
                    # $string1 & $string2 are objects!
            }

            if ($string1->get_value eq $string2->get_value)
            {
                    # RIGHT!!!
                    # now you're comparing actual strings...
            }

Arrays - new style!
    Arrays are created with the 'create_array' function call. It needs a
    fully-qualified java object or primitive name and a dimension.

            If you specified 'use_tied_arrays' in your constructor to Java.pm
            (& I think you should unless you have to perserve backwards 
            compatibility...) all Java array references will be 'tied' to the
            JavaArray class allowing a more intuitive interface to your array.

            All array references will be _references_ to these objects.  
            Here's how it looks (compare with 'old style' below):

            # This will create a String array with 100 elements
        #       (this is the same)
            my $array  = $java->create_array("java.lang.String",100);

        # Now it gets interesting!
            # Don't forget on primitive arrays to use the ':' notation!
            $array->[22] = "Mark rules the free world";

            # Get element #99
            my $element_99 = $array->[99];

    To get the length or size of an array do what you'd expect (I hope!)

    For example:

            my $length = scalar (@$array);
            my $size = $#{@array};

            (remember you get an arrayref there sonny...)

    To pass as a function parameter just pass it in as normal:

            my $list = $java->java_util_Arrays("asList",$array);

Arrays - old style
    Arrays are created with the 'create_array' function call. It needs a
    fully-qualified java object or primitive name and a dimension.

    For example:

            # This will create a char array with 100 elements
            my $char_array  = $java->create_array("char",100);

            # This will create a String array with 5 elements
            my $string_array = $java->create_array("java.lang.String",5);
                
    Array elements are get and set using the 'get_field' and 'set_field'
    function calls.

    For example:

            # Set element #22 to 'B'
            # Don't forget on primitive arrays to use the ':' notation!
            $char_array->set_field(22,"B:char");

            # Set element #3 to 'Mark Rox'
            $string_array->set_field(3,"Mark Rox");

            # Get element #99
            my $element_99 = $char_array->get_field(99);

            # Get element #4
            my $element_4 = $string_array->get_field(4);

            # Don't forget to get the actual string value you gotta call
            #       'get_value'!
            my $char_value = $char_element_99->get_value;
            my $string_value = $string_element_4->get_value;

    To get the length of an array use the get_length function.

    For example:

            my $length = $string_array->get_length;

    Note this will return an actual integer! You do not need to call
    'get_value' on 'get_length's return value!

Passing & receiving the 'null' value
    To pass a 'null' in a function parameter list or to set a field or array
    index, used Perl's 'undef'. So:

            $object->function($param1, undef, $param2);

    Will pass 'null' as the second parameter to that function. Similarly to
    set a field or array index to null:

            $object->set_field("fieldname",undef);  # Set field to null
            $array->[4] = undef;    # Set array value to null

    Of course if the field or array type is a primimtive type you will get a
    NullPointerException - Java doesn't seem to like that!

    If a function returns null or a field or array index is equal to null,
    you will recieve 'undef' back. Note this is indistinguishable (sp??)
    from a function with a 'void' return value. So:

            my $retval = $object->function($param1,$param2,undef,"Another param");
            print "It returned NULL\n" if (!$retval);

    Similarly:

            my $f_value = $object->get_field("someField");
            print "someField is NULL\n" if (!$f_value);

            my $a_value = $array->[38];
            print "Array index 38 is NULL\n" if (!$a_value);

    If someone can think of a good reason why the null return value should
    not be undef or should be different than what a void function returns
    I'd like to hear about it!

Exceptions
    Currently Java.pm will 'croak' when an Exception is encountered in
    JavaServer. So the way to deal with them is to enclose your Java
    expression that might throw an exception in an 'eval' block & then check
    the $@ variable to see if an Exception was indeed thrown. You then need
    to parse the $@ variable to see exactly what Exception was thrown.
    Currently the format of the $@ string is:

            ERROR: java.lang.Exception: some.java.Exception: <more info> at $0 line XX

    Note the '<more info>' part is the result of the getMessage() function
    of that Exception. Everything after that is the stuff put in there by
    croak; the filename & line number of your Perl program.

  get_exception
    The actual Exception object that was thrown is available via the
    'get_exception' function call.

  get_stack_trace
    There is also a convenience function 'get_stack_trace' which will return
    the Stack Trace as an array of lines from the most recent Exception
    thrown. To see how this is done 'Read The Code Luke' in Java.pm -
    basically it just gets the most recent Exception & creates an
    appropriate PrintWriter into which it has Java dump the Stack Trace &
    then it just returns the String-ifized version of it - something you can
    easily (albiet messily) do yourself.


    So here's what an Exception handler can look like:

            my $I;
            eval
            {
                    $I = $java->java_lang_Integer("parseInt","$some_string:string");
            };
            if ($@)
            {
                    # An exception was thrown!!
                    $@ =~ s/^ERROR: //;     # Gets rid of 'ERROR: '
                    $@ =~ s/at $0.*$//;     # Gets rid of 'croak' generated stuff

                    # Print just the Java stuff
                    print "$@\n";

                    # This is the actual NumberFormatException object
                    my $exception_object = $java->get_exception;

                    # There's also this new convenience routines to give
                    #       the Stack Trace as an array of lines
                    # This returns the Stack Trace from the most recent
                    #       Exception thrown 
                    my @stack_trace = $java->get_stack_trace;

                    local($") = "\n";
                    print "Stack Trace:\n@st\n";

            }

    So in this example if the scalar $some_string did NOT contain a parsable
    integer - say 'dd' - the printed error message would be:

            java.lang.Exception: java.lang.NumberFormatException: dd 

            Stack Trace:
            java.lang.Exception: java.lang.NumberFormatException: dd
                    at Dealer.callFunction(Dealer.java:856)
                    at Dealer.parse(Dealer.java:526)
                    at Dealer.run(Dealer.java:425)

    You can most likely ignore all of the 'Dealer' stack frames as that is
    internal to JavaServer. Of course dumping Stack Traces should only be
    used while you're debugging anyways!

Comparing Java objects
    The '==' operator is now overloaded to provide this functionality!
    Woohoo! So you can now say stuff like:

            if ($object1 == $object2)
            {
                    #They're the same!
            }
            else
            {
                    #Not!
            }

    Here's the old (other) way of doing the exact same thing:

    You can see if two references to java objects actually point to the same
    object by using the 'same' function like:

            if ($object1->same($object2))
            {
                    # They're the same!
            }
            else
            {
                    # Nope, not the same
            }

    You'll see why this is useful in the next section 'Events'.

Events
    Events are passed from the remote JVM to Perl5 via a separate event
    port. To enable events on an object use the 'do_event' function. Your
    callback function will receive the object that caused the event as its
    first parameter and the event object itself as the second parameter.
    Here's where ya wanna use the 'same' function (or the new overloaded
    '==' operator) to see what object caused this event if you set up
    multiple objects to call the same event function.

    For example:

            my $frame = $java->create_object("java.awt.Frame","Title");
            $java->do_event($frame,"addWindowListener",\&event_handler);
            my $button = $java->create_object("java.awt.Button","Push Me");
            $java->do_event($button,"addActionListener",\&event_handler);

    To stop listening for events do:

            $java->do_event($frame,"removeWindowListener");

    Where: - $frame is the object for which you'd like to receive events -
    "addWindowListener" specifies the types of events you want to listen for
    - \&event_handler is your event callback routing that will handle these
    events

    You will keep receiving events you registered for until you make a
    "remove" call or your Java object goes away (out of scope, you destroy
    it, whatever).

    Note the second parameter MUST be of the form:

            "<add | remove><Event Type>Listener"

    Default <Event Types> are:

            Component
            Container
            Focus
            Key
            Mouse
            MouseMotion
            Window
            Action
            Item
            Adjustment
            Text

    Swing <Event Types> are:

            Ancestor
            Caret
            CellEditor
            Change
            Hyperlink
            InternalFrame
            ListData
            ListSelection
            MenuDragMouse
            MenuKey
            Menu
            PopupMenu
            TreeExpansion
            TreeSelection
            TreeWillExpand

    And within most of these <Event Types> there are a number of specific
    events. Check out the Java event docs if you don't know what I'm talking
    about...

    Here's what an event handler looks like:

            sub event_handler
            {
                    my($object,$event) = @_;
                    if ($object->same($frame))      # Old sytle
                            OR
                    if ($object == $frame)          # New style!
                    {
                            # Event caused by our frame object!
        
                            # This will get this event's ID value
                            my $event_id = $event->getID->get_value;

                            # Get value for a WINDOW_CLOSING event
                            my $closing_id = $java->get_field("java.awt.event.WindowEvent","WINDOW_CLOSING")->get_value;

                            if ($event_id == $closing_id)
                            {
                                    # Close our frame @ user request
                                    $object->dispose;
                            }
                    }
                    if ($object->same($button))     # old style
                            OR
                    if ($object == $button)         # new style!
                    {
                            print "You Pushed My Button!\n";
                    }
            }

    Note return values from event handlers are ignored by Java.pm BUT are
    returned from the Event Loop as you'll see in a bit.

    Note also how I had to call 'get_value' to get the actualy integer
    values of the 'getID' function return value and the field value of
    WINDOW_CLOSING.

Event Loops
    Once you've set up your event handlers you must start the event loop to
    begin getting events - there are two ways to do this.

            1. Have Java.pm handle the event loop 
            2. Roll your own.

    Java.pm's event loop will block until an events happens - typically this
    is what you want but sometimes you might want more control, so I've
    decided to be nice this _one_ time & let you roll your own too.

    Here's how Java.pm's event loop works for ya:

            #
            # Set up a bunch of events...
            #

            while(1)
            {
                    my $cont = $java->go;
                    last if (!defined $cont);
            }

    Note this works similarly to Tk's event loop. Your program will now just
    sit & respond to events via your event handlers. Also note that
    Java.pm's event loop only handles ONE event & then returns - the return
    value is whatever your event handler returned OR undef if there was an
    error (like you lost yer connexion to the JVM).

    Here's how you can create yer own Event Loop:

    You ask Java.pm for a FileHandle that represents the incoming event
    stream. You can then select on this FileHandle or do whatever else you
    want - remember this is a READ ONLY FileHandle so writing to it ain't
    going to do anything. Once you get a 'line' from this FileHandle you can
    (and probably should) call 'decipher_event' & the event will be
    dispatched to your event handler appropriately - the return value being
    the return value of your event handler. This can look something like
    this:

            ## Roll my own event loop

            # Get event FileHandle
            my $event_file_handle = $java->get_event_FH;

            # Set up my select loop
            my $READBITS = 0;
            vec($READBITS,$event_file_handle->fileno,1) = 1;

            # Suck in lines forever & dispatch events
            while(1)
            {
                    my $nf = select(my $rb = $READBITS,undef,undef,undef);
                    if ($nf)
                    {
                            my $event_line = <$event_file_handle>;
                            $java->decipher_event($event_line);
                    }
            }

    Note this example is EXACTLY what Java.pm's 'go' function does - if you
    roll yer own Event Loop you prolly want to do something more interesting
    than this!

    The upshot is you'll probably just want to use the 'go' function but if
    you've got some other FileHandles going on & you don't want to block on
    just this one you can (and should) use the 'roll your own' method.

Authorization
    Using the 'authfile' key when creating the root Java object specifies a
    file whose first line is taken to be a password to be passed to the
    remote JavaServer to authenticate the connexion. JavaServer must be
    started with the '--authfile=<filename>' command-line option and the
    first line of that file must match to be granted access. Note this is a
    _very_ basic form of authorization - to maximize it you should restrict
    the file permissions as much as possible (i.e. 0600). Thanks to Achim
    Settelmeier for the initial implementation!

EXPORT
    None by default.

AUTHOR
    Mark Ethan Trostler, mark@zzo.com

SEE ALSO
    perl(1). http://www.javasoft.com/. Any sorta Java documentation you can
    get yer hands on! http://www.zzo.com/Java/getit.html

COPYRIGHT
    Copyright (c) 2000-2003 Mark Ethan Trostler

    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)

