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INT-1438, added XPath transformer documentation

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This commit is contained in:
Oleg Zhurakousky
2010-09-15 22:43:41 -04:00
parent d5cb033c60
commit 394efd2a2a
2 changed files with 100 additions and 2 deletions
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spring-integration-xml/src/main/java/org/springframework/integration/xml/XmlPayloadConverter.java
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/*
* Copyright 2002-2008 the original author or authors.
* Copyright 2002-2010 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.

100
src/docbkx/xml.xml
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<chapter id="xml">
<title>Dealing with XML Payloads</title>
<title>XML Support - Dealing with XML Payloads</title>
<section id="xml-intro">
<title>Introduction</title>
@@ -328,6 +328,104 @@
</bean>]]></programlisting>
</section>
<section id="xpath-transformer">
<title>Transforming xml messages using XPath</title>
<para>
When it comes to message transformation XPath is a great way to transform Messages that have XML
payloads by defining XPath transformers via <emphasis>xpath-transformer</emphasis> element.
</para>
<para>
<emphasis>Simple XPath transformation</emphasis>
</para>
<para>
Let's look at the following transformer configuration:
<programlisting language="xml"><![CDATA[<xpath-transformer input-channel="inputChannel" output-channel="outputChannel"
xpath-expression="/person/@name" />]]></programlisting>
. . . and Message
<programlisting language="java"><![CDATA[Message<?> message =
MessageBuilder.withPayload("<person name='John Doe' age='42' married='true'/>").build();]]></programlisting>
After sending this message to the 'inputChannel' the XPath transformer configured above will transform
this XML Message to a simple Message with payload of 'John Doe' all based on
the simple XPath Expression specified in the <emphasis>xpath-expression</emphasis> attribute.
</para>
<para>
XPath also has capability to perform simple conversion of extracted elements
to a desired type. Valid return types are defined in <classname>XPathConstants</classname> and follows
the conversion rules specified by the <classname>XPath</classname>.
</para>
<para>
The following constants are defined by the <classname>XPathConstants</classname>: <emphasis>BOOLEAN, DOM_OBJECT_MODEL, NODE, NODESET, NUMBER, STRING</emphasis>
</para>
<para>
You can configure the desired type by simply using <emphasis>evaluation-type</emphasis>
attribute of the <emphasis>xpath-transformer</emphasis> element.
<programlisting language="xml"><![CDATA[<xpath-transformer input-channel="numberInput" xpath-expression="/person/@age"
evaluation-type="NUMBER_RESULT" output-channel="output"/>
<xpath-transformer input-channel="booleanInput" xpath-expression="/person/@married = 'true'"
evaluation-type="BOOLEAN_RESULT" output-channel="output"/>
]]></programlisting>
</para>
<para>
<emphasis>Node Mappers</emphasis>
</para>
<para>
If you need to provide custom mapping for the node extracted by the XPath expression simply provide a reference to the
implementation of the <classname>org.springframework.xml.xpath.NodeMapper</classname> - an interface used by
<classname>XPathOperations</classname> implementations for mapping Node objects on a per-node basis. To provide a
reference to a <classname>NodeMapper</classname> simply use <emphasis>node-mapper</emphasis> attribute:
<programlisting language="xml"><![CDATA[<xpath-transformer input-channel="nodeMapperInput" xpath-expression="/person/@age"
node-mapper="testNodeMapper" output-channel="output"/>
]]></programlisting>
. . . and Sample NodeMapper implementation:
<programlisting language="java"><![CDATA[class TestNodeMapper implements NodeMapper {
public Object mapNode(Node node, int nodeNum) throws DOMException {
return node.getTextContent() + "-mapped";
}
}]]></programlisting>
</para>
<para>
<emphasis>XML Payload Converter</emphasis>
</para>
<para>
You can also use implementation of the <classname>org.springframework.integration.xml.XmlPayloadConverter</classname> to
provide more granular transformation:
<programlisting language="xml"><![CDATA[<xpath-transformer input-channel="customConverterInput" xpath-expression="/test/@type"
converter="testXmlPayloadConverter" output-channel="output"/>
]]></programlisting>
. . . and Sample XmlPayloadConverter implementation:
<programlisting language="java"><![CDATA[class TestXmlPayloadConverter implements XmlPayloadConverter {
public Source convertToSource(Object object) {
throw new UnsupportedOperationException();
}
//
public Node convertToNode(Object object) {
try {
return DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(
new InputSource(new StringReader("<test type='custom'/>")));
}
catch (Exception e) {
throw new IllegalStateException(e);
}
}
//
public Document convertToDocument(Object object) {
throw new UnsupportedOperationException();
}
}]]></programlisting>
</para>
<para>
<emphasis>Combination of SpEL and XPath expressions</emphasis>
</para>
<para>
You can also combine Spring Expression Language (SpEL) expressions with XPath expression and configure
them using <emphasis>expression</emphasis> attribute:
<programlisting language="xml"><![CDATA[xpath-expression id="testExpression" expression="/person/@age * 2"/>]]></programlisting>
In the above case the overall result of the expression will be the result of the XPathe expression multiplied by 2.
</para>
</section>
<section id="xpath-namespace-support">
<title>XPath components namespace support</title>