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<!-- $Id: sax-2.0.html,v 1.6 2002/01/21 19:21:43 darobin Exp $ -->
<html>
<head>
<title>Perl SAX 2.0 Binding</title>
</head>
<body>
<h1>Perl SAX 2.0 Binding</h1>
<p>SAX (Simple API for XML) is a common parser interface for XML
parsers. It allows application writers to write applications that use
XML parsers, but are independent of which parser is actually used.</p>
<p>This document describes the version of SAX used by Perl modules.
The original version of SAX 2.0, for Java, is described at <a
href="http://sax.sourceforge.net/">http://sax.sourceforge.net/</a>.</p>
<p>There are two basic interfaces in the Perl version of SAX, the
parser interface and the handler interface. The parser interface
creates new parser instances, starts parsing, and provides additional
information to handlers on request. The handler interface is used to
receive parse events from the parser. This pattern is also commonly
called "Producer and Consumer" or "Generator and Sink". Note that the
parser doesn't have to be an XML parser, all it needs to do is provide
a stream of events to the handler as if it were parsing XML. But the
actual data from which the events are generated can be anything, a Perl
object, a CSV file, a database table...
</p>
<p>SAX is typically used like this:
<pre>
my $handler = MyHandler->new();
my $parser = AnySAXParser->new( Handler => $handler );
$parser->parse($uri);
</pre></p>
<p>Handlers are typically written like this:
<pre>
package MyHandler;
sub new {
my $type = shift;
return bless {}, $type;
}
sub start_element {
my ($self, $element) = @_;
print "Starting element $element->{Name}\n";
}
sub end_element {
my ($self, $element) = @_;
print "Ending element $element->{Name}\n";
}
sub characters {
my ($self, $characters) = @_;
print "characters: $characters->{Data}\n";
}
1;
</pre></p>
<h2>Basic SAX Parser</h2>
<p>These methods and options are the most commonly used with SAX
parsers and event generators.</p>
<p>Applications may not invoke a <tt>parse()</tt> method again while a
parse is in progress (they should create a new SAX parser instead for
each nested XML document). Once a parse is complete, an application
may reuse the same parser object, possibly with a different input
source.</p>
<p>During the parse, the parser will provide information about the XML
document through the registered event handlers. Note that an event that
hasn't been registered (ie that doesn't have its corresponding method in
the handler's class) will <b>not</b> be called. This allows one to only
get the events one is interested in.
</p>
<p>
<dl><dt><b><tt class='function'>parse</tt></b>(<var>uri</var> [, <var>options</var>])</dt>
<dd>
Parses the XML instance identified by <var>uri</var> (a system
identifier). <var>options</var> can be a list of option, value pairs
or a hash. Options include <tt>Handler</tt>, features and properties,
and advanced SAX parser options. <tt>parse()</tt> returns the result
of calling the <tt>end_document()</tt> handler. The options supported
by <tt>parse()</tt> may vary slightly if what is being "parsed" isn't
XML.
</dd></dl></p>
<p>
<dl><dt><b><tt class='function'>parse_file</tt></b>(<var>stream</var> [, <var>options</var>])</dt>
<dd>
Parses the XML instance in the already opened <var>stream</var>, an
IO::Handler or similar. <var>options</var> are the same as for <tt
class='function'>parse()</tt>. <tt>parse_file()</tt> returns the result
of calling the <tt>end_document()</tt> handler.</dd></dl></p>
<p>
<dl><dt><b><tt class='function'>parse_string</tt></b>(<var>string</var> [, <var>options</var>])</dt>
<dd>
Parses the XML instance in <var>string</var>. <var>options</var> are
the same as for <tt class='function'>parse()</tt>.
<tt>parse_string()</tt> returns the result of calling the
<tt>end_document()</tt> handler.</dd></dl></p>
<p>
<dl><dt><b><tt>Handler</tt></b></dt>
<dd>
The default handler object to receive all events from the parser.
Applications may change <tt>Handler</tt> in the middle of the parse
and the SAX parser will begin using the new handler
immediately. The <a href="sax-2.0-adv.html">Advanced SAX</a> document
lists a number of more specialized handlers that can be used should you
wish to dispatch different types of events to different objects.
</dd></dl></p>
<h2><a name="BasicHandler">Basic SAX Handler</a></h2>
<p>These methods are the most commonly used by SAX handlers.</p>
<p>
<dl><dt><b><tt class='function'>start_document</tt></b>(<var>document</var>)</dt>
<dd>
Receive notification of the beginning of a document.
<p>The SAX parser will invoke this method only once, before any other
methods (except for <tt>set_document_locator()</tt> in advanced SAX
handlers).</p>
No properties are defined for this event (<var>document</var> is
empty).</dd></dl></p>
<p>
<dl><dt><b><tt class='function'>end_document</tt></b>(<var>document</var>)</dt>
<dd>
Receive notification of the end of a document.
<p>The SAX parser will invoke this method only once, and it will be
the last method invoked during the parse. The parser shall not invoke
this method until it has either abandoned parsing (because of an
unrecoverable error) or reached the end of input.</p>
<p>No properties are defined for this event (<var>document</var> is
empty).</p>
The return value of <tt>end_document()</tt> is returned by the
parser's <tt>parse()</tt> methods.</dd></dl></p>
<p>
<dl><dt><b><tt class='function'>start_element</tt></b>(<var>element</var>)</dt>
<dd>
Receive notification of the start of an element.
<p>The Parser will invoke this method at the beginning of every
element in the XML document; there will be a corresponding
<tt>end_element()</tt> event for every <tt>start_element()</tt> event (even when the
element is empty). All of the element's content will be reported, in
order, before the corresponding <tt>end_element()</tt> event.</p>
<var>element</var> is a hash with these properties:
<blockquote>
<table>
<tr><td><b><tt>Name</tt></b></td>
<td>The element type name (including prefix).</td></tr>
<tr><td><b><tt>Attributes</tt></b></td>
<td>The attributes attached to the element, if any.</td></tr>
</table>
</blockquote>
If namespace processing is turned on (which is the default), these
properties are also available:
<blockquote>
<table>
<tr><td><b><tt>NamespaceURI</tt></b></td>
<td>The namespace of this element.</td></tr>
<tr><td><b><tt>Prefix</tt></b></td>
<td>The namespace prefix used on this element.</td></tr>
<tr><td><b><tt>LocalName</tt></b></td>
<td>The local name of this element.</td></tr>
</table>
</blockquote>
<tt>Attributes</tt> is a hash keyed by JClark namespace notation. That
is, the keys are of the form "{NamespaceURI}LocalName". If the attribute
has no NamespaceURI, then it is simply "{}LocalName". Each attribute is
a hash with these properties:
<blockquote>
<table>
<tr><td><b><tt>Name</tt></b></td>
<td>The attribute name (including prefix).</td></tr>
<tr><td><b><tt>Value</tt></b></td>
<td>The normalized value of the attribute.</td></tr>
<tr><td><b><tt>NamespaceURI</tt></b></td>
<td>The namespace of this attribute.</td></tr>
<tr><td><b><tt>Prefix</tt></b></td>
<td>The namespace prefix used on this attribute.</td></tr>
<tr><td><b><tt>LocalName</tt></b></td>
<td>The local name of this attribute.</td></tr>
</table>
</blockquote>
</dd>
</dl>
</p>
<p>
<dl><dt><b><tt class='function'>end_element</tt></b>(<var>element</var>)</dt>
<dd>
Receive notification of the end of an element.
<p>The SAX parser will invoke this method at the end of every element
in the XML document; there will be a corresponding <tt
class='function'>start_element()</tt> event for every <tt
class='function'>end_element()</tt> event (even when the element is
empty).</p>
<var>element</var> is a hash with these properties:
<blockquote>
<table>
<tr><td><b><tt>Name</tt></b></td>
<td>The element type name (including prefix).</td></tr>
</table>
</blockquote>
If namespace processing is turned on (which is the default), these
properties are also available:
<blockquote>
<table>
<tr><td><b><tt>NamespaceURI</tt></b></td>
<td>The namespace of this element.</td></tr>
<tr><td><b><tt>Prefix</tt></b></td>
<td>The namespace prefix used on this element.</td></tr>
<tr><td><b><tt>LocalName</tt></b></td>
<td>The local name of this element.</td></tr>
</table>
</blockquote></dd>
</dl></p>
<p>
<dl><dt><b><tt class='function'>characters</tt></b>(<var>characters</var>)</dt>
<dd>
Receive notification of character data.
<p>The Parser will call this method to report each chunk of character
data. SAX parsers may return all contiguous character data in a
single chunk, or they may split it into several chunks (however, all
of the characters in any single event must come from the same external
entity so that the Locator provides useful information).</p>
<p><var>characters</var> is a hash with this property:</p>
<blockquote>
<table>
<tr><td><b><tt>Data</tt></b></td>
<td>The characters from the XML document.</td></tr>
</table>
</blockquote></dd>
</dl></p>
<p>
<dl><dt><b><tt class='function'>ignorable_whitespace</tt></b>(<var>characters</var>)</dt>
<dd>
Receive notification of ignorable whitespace in element content.
<p>Validating Parsers must use this method to report each chunk of
ignorable whitespace (see the W3C XML 1.0 recommendation, section
2.10): non-validating parsers may also use this method if they are
capable of parsing and using content models.</p>
<p>SAX parsers may return all contiguous whitespace in a single chunk,
or they may split it into several chunks; however, all of the
characters in any single event must come from the same external
entity, so that the Locator provides useful information.</p>
<p><var>characters</var> is a hash with this property:</p>
<blockquote>
<table>
<tr><td><b><tt>Data</tt></b></td>
<td>The whitespace characters from the XML document.</td></tr>
</table>
</blockquote></dd>
</dl></p>
<h2><a name="Exceptions">Exceptions</a></h2>
<p>
Conformant XML parsers are required to abort processing when
well-formedness or validation errors occur. In Perl, SAX parsers use
<tt>die()</tt> to signal these errors. To catch these errors and prevent
them from killing your program, use <tt>eval{}</tt>:
<pre>
eval { $parser->parse($uri) };
if ($@) {
# handle error
}
</pre>
</p>
<p>
Exceptions can also be thrown when setting features or properties
on the SAX parser (see advanced SAX below).</p>
<p>
Exception values (<tt>$@</tt>) in SAX are hashes blessed into the
package that defines their type, and have the following properties:
</p>
<blockquote>
<table>
<tr><td><b><tt>Message</tt></b></td>
<td>A detail message for this exception.</td></tr>
<tr><td><b><tt>Exception</tt></b></td>
<td>The embedded exception, or <tt>undef</tt> if there is none.</td></tr>
</table>
</blockquote>
If the exception is raised due to parse errors, these
properties are also available:
<blockquote>
<table>
<tr><td><b><tt>ColumnNumber</tt></b></td>
<td>The column number of the end of the text where the exception
occurred.</td></tr>
<tr><td><b><tt>LineNumber</tt></b></td>
<td>The line number of the end of the text where the exception
occurred.</td></tr>
<tr><td><b><tt>PublicId</tt></b></td>
<td>The public identifier of the entity where the exception
occurred.</td></tr>
<tr><td><b><tt>SystemId</tt></b></td>
<td>The system identifier of the entity where the exception
occurred.</td></tr>
</table>
</blockquote>
<p></p><hr />
<h2>Advanced SAX</h2>
<ul>
<li><a href="sax-2.0-adv.html#Parsers">SAX Parsers</a></li>
<li><a href="sax-2.0-adv.html#Features">Features</a></li>
<li><a href="sax-2.0-adv.html#InputSources">Input Sources</a></li>
<li><a href="sax-2.0-adv.html#Handlers">SAX Handlers</a></li>
<li><a href="sax-2.0-adv.html#Filters">SAX Filters</a></li>
<li><a href="sax-2.0-adv.html#Java">Java and DOM Compatibility</a></li>
</ul>
</body>
</html>
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