9.4.1. First Example: A Temperature Converter

9.4.2. Second Example: An ISBN Lookup Engine

This example, which uses a little module residing on one of the author's personal web servers, is somewhat more object oriented. It takes an ISBN number and returns Dublin Core XML for almost any book that might match it:

  my ($isbn_number) = @ARGV;
  use SOAP::Lite +autodispatch=>
      uri=>'http://www.jmac.org/ISBN',
      proxy=>'http://www.jmac.org/projects/bookdb/isbn/lookup.pl';
  my $isbn_obj = ISBN->new;

  # The 'get_dc' method fetches Dublin Core information
  my $result = $isbn_obj->get_dc($isbn_number);

The magic here is that the module on the host machine, ISBN.pm, isn't unusual in any way; it's a pretty straightforward Perl module that you could use in the usual fashion, if you happened to have a local copy. In other words, we can get the same results by logging into the machine and hammering out a little program like this:

  my ($isbn_number) = @ARGV;
  use ISBN; # This line replaces the long 'use SOAP::Lite' line
  my $isbn_obj = ISBN->new;

  # The 'get_dc' method fetches Dublin Core information
  my $result = $isbn_obj->get_dc($isbn_number);

But, by invoking SOAP::Lite and mumbling a few extra incantations to aim our sights at a remote machine that's listening for SOAP-ish requests, you don't need a copy of that Perl module on your end to enjoy the benefits of its API. And, if we eventually went insane and reimplemented the module in Java, you'd probably never know it, since we'd keep the interface the same. In the language-independent world of web services, that's all that matters.

Where is the XML? We can switch on a valve and peek at the raw stuff roaring beneath this pleasant veneer. Let's see what actually happens with that ISBN class constructor call after we activate SOAP::Lite's outputxml option:

  my ($isbn_number) = @ARGV;
  use SOAP::Lite +autodispatch=>
      uri=>'http://www.jmac.org/ISBN', outputxml=>1,
      proxy=>'http://www.jmac.org/projects/bookdb/isbn/lookup.pl';
  my $isbn_xml = ISBN->new;
  print "$isbn_xml\n";

What we get back is something like this:

<?xml version="1.0" encoding="UTF-8"?><SOAP-ENV:Envelope xmlns:SOAP-ENC="http://
schemas.xmlsoap.org/soap/encoding/" SOAP-ENV:encodingStyle="http://schemas.xmlsoap.
org/soap/encoding/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:
xsi="http://www.w3.org/1999/XMLSchema-instance" xmlns:xsd="http://www.w3.org/1999/
XMLSchema" xmlns:namesp1="http://www.jmac.org/ISBN"><SOAP-ENV:Body><namesp2:
newResponse xmlns:namesp2="http://www.jmac.org/ISBN"><ISBN xsi:type="namesp1:ISBN"/>
</namesp2:newResponse></SOAP-ENV:Body></SOAP-ENV:Envelope>

The second bit of example code had to stop short, of course, since it returned a scalar containing a pile of XML (which we then printed) instead of an object belonging to the SOAP::Lite class family. We can't well continue calling methods on it. We can fix this problem by passing the blob to the magic SOAP::Deserializer class, which turns SOAPy XML back into objects:

# Continuing from the previous snippet...
my $deserial = SOAP::Deserializer->new;
my $isbn_obj = $deserial->deserialize($isbn_xml);
# Now we can continue as with the first example.

A little extra work, then, nets us the raw XML as well as the black boxes of the SOAP::Lite objects. As you may expect, this feature has uses far beyond interesting book examples, as getting the raw XML in hand opens up the door to all kinds of interesting mischief on our end.