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<h1>Writing input filters</h1>
<p>Saxon can take its input from a JAXP <code>SAXSource</code> object, which essentially represents a sequence
of SAX events representing the output of an XML parser. A very useful technique is to
interpose a <i>filter</i> between the parser and Saxon. The filter will typically be an
instance of the SAX2 <b>XMLFilter</b> class.
</p>
<p>There are a number of ways of using a Saxon XSLT transformation as part of a pipeline of filters.
Some of these techniques also work with XQuery. The techniques include:</p>
<ul>
<li content="para">
<p>Generate the transformation as an <code>XMLFilter</code> using the <code>newXMLFilter()</code>
method of the <code>TransformerFactory</code>. This works with XSLT only. A drawback of this approach
is that it is not possible to supply parameters to the transformation using standard JAXP facilities. It
is possible, however, by casting the <code>XMLFilter</code> to a <a class="bodylink" href="../javadoc/net/sf/saxon/Filter.html"><code>net.sf.saxon.Filter</code></a>, and calling
its <code>getTransformer()</code> method, which returns a <code>Transformer</code> object offering the usual
<code>addParameter()</code> method.</p>
</li>
<li content="para">
<p>Generate the transformation as a SAX <code>ContentHandler</code> using the <code>newTransformerHandler()</code>
method. The pipelines stages after the transformation can be added by giving the transformation a <code>SAXResult</code>
as its destination. This again is XSLT only.</p>
</li>
<li content="para">
<p>Implement the pipeline step before the transformation or query as an <code>XMLFilter</code>, and
use this as the <code>XMLReader</code> part of a <code>SAXSource</code>, pretending to be an XML parser.
This technique works with both XSLT and XQuery, and it can even be used from the command line, by nominating
the <code>XMLFilter</code> as the source parser using the <code>-x</code> option on the command line.</p>
</li>
</ul>
<p>The <code>-x</code> option on the Saxon command line specifies the parser that Saxon will
use to process the source files. This class must implement the SAX2 XMLReader interface, but it
is not required to be a real XML parser; it can take the input from any kind of source file,
so long as it presents it in the form of a stream of SAX events. When using the JAXP API, the
equivalent to the <code>-x</code> option is to call <code>transformerFactory.setAttribute(
net.sf.saxon.lib.FeatureKeys.SOURCE_PARSER_CLASS, 'com.example.package.Parser')</code></p>
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