Using the exception catcher processor in XPL, with Orbeon Forms

gistfile1.xml

<?xml version="1.0" encoding="utf-8"?>
<p:config xmlns:p="http://www.orbeon.com/oxf/pipeline"
          xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
          xmlns:oxf="http://www.orbeon.com/oxf/processors">

    <p:param name="instance" type="input"/>
    <p:param name="data" type="output"/>

    <!-- Using the URL generator, which here will 404 -->
    <p:processor name="oxf:url-generator">
        <p:input name="config">
            <config>
                <url>http://www.google.com/notfound</url>
            </config>
        </p:input>
        <p:output name="data" id="url-data"/>
    </p:processor>

    <!-- The exception catcher behaves like the identity processor if there is no exception -->
    <!-- However if there is an exception, it catches it, and you get a serialized form of the exception -->
    <p:processor name="oxf:exception-catcher">
        <p:input name="data" href="#url-data"/>
        <p:output name="data" id="url-data-checked"/>
    </p:processor>

    <!-- Check whether we had an exception -->
    <p:choose href="#url-data-checked">
        <p:when test="/exceptions">
            <!-- Extract the message -->
            <p:processor name="oxf:xslt">
                <p:input name="data" href="#url-data-checked"/>
                <p:input name="config">
                    <message xsl:version="2.0">
                        <xsl:value-of select="/exceptions/exception/message"/>
                    </message>
                </p:input>
                <p:output name="data" ref="data"/>
            </p:processor>
        </p:when>
        <p:otherwise>
            <!-- Just return the document -->
            <p:processor name="oxf:identity">
                <p:input name="data" href="#url-data-checked"/>
                <p:output name="data" ref="data"/>
            </p:processor>
        </p:otherwise>
    </p:choose>

</p:config>