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INT-3119 Add Documentation Re SpEL Customization

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- Custom PropertyAccessors
- Custom Functions

Polishing - PR Comments
This commit is contained in:
Gary Russell
2013-08-30 14:16:53 -04:00
parent 8f182a2be8
commit 693a1e17a0
5 changed files with 100 additions and 3 deletions
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1
src/reference/docbook/index.xml
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@@ -162,6 +162,7 @@
<partintro id="spring-integration-adapters">
<para>Advanced Topics and Additional Resources</para>
</partintro>
<xi:include href="./spel.xml"/>
<xi:include href="./message-publishing.xml"/>
<xi:include href="./transactions.xml"/>
<xi:include href="./security.xml"/>

88
src/reference/docbook/spel.xml Normal file
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@@ -0,0 +1,88 @@
<?xml version="1.0" encoding="UTF-8"?>
<appendix xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="spel"
xmlns:xlink="http://www.w3.org/1999/xlink">
<title>Spring Expression Language (SpEL)</title>
<section id="spel-intro">
<title>Introduction</title>
<para>
Many Spring Integration components can be configured using expressions. These expressions
are written in the <ulink url="http://static.springsource.org/spring-framework/docs/current/spring-framework-reference/html/expressions.html">
Spring Expression Language</ulink>.
</para>
<para>
In most cases, the <emphasis>#root</emphasis> object is the
<classname>Message</classname> which, of course, has two properties - <code>headers</code> and
<code>payload</code> - allowing such expressions as <code>payload</code>, <code>payload.foo</code>,
<code>headers['my.header']</code> etc.
</para>
<para>
In some cases, additional variables are provided, for example the <code>&lt;int-http:inbound-gateway/&gt;</code>
provides <code>#requestParams</code> (parameters from the HTTP request) and <code>#pathVariables</code>
(values from path placeholders in the URI).
</para>
<para>
For all SpEL expressions, a <interfacename>BeanResolver</interfacename> is available, enabling references to
any bean in the application context. For example <code>@myBean.foo(payload)</code>. In addition, two
<interfacename>PropertyAccessors</interfacename> are available; a <classname>MapAccessor</classname>
enables accessing values in a <interfacename>Map</interfacename> using a key, and a
<classname>ReflectivePropertyAccessor</classname> which allows access to fields and or JavaBean compliant
properties (using getters and setters). This is how the <interfacename>Message</interfacename> headers
and payload properties are accessible.
</para>
<para>
Starting with Spring Integration 3.0, it is possible to add additional
<interfacename>PropertyAccessor</interfacename>s to the SpEL evaluation context.
In fact, the framework provides one such accessor,
the <classname>JsonPropertyAccessor</classname> which can be used (read-only) to access fields from
a <classname>JsonNode</classname>, or JSON in a <classname>String</classname>. Or you can create your
own <interfacename>PropertyAccessor</interfacename> if you have specific needs.
</para>
<para>
In addition, custom functions can be added. Custom functions are <code>static</code> methods
declared on a class. Functions and property accessors are available in any SpEL
expression used throughout the framework.
</para>
<para>
To configure your custom accessors and functions, add an
<classname>IntegrationEvaluationContextFactoryBean</classname> with
<code>id="integrationEvaluationContext"</code>
to your application context, with the appropriate configuration; for example:
</para>
<programlisting language="xml"><![CDATA[<beans:bean id="integrationEvaluationContext"
class="org.springframework.integration.config.IntegrationEvaluationContextFactoryBean">
<property name="propertyAccessors">
<list>
<bean class="foo.MyCustomPropertyAccessor"/>
</list>
</property>
<property name="functions">
<map>
<entry key="barcalc"
value="#{T(foo.MyFunctions).getMethod('calc', T(foo.MyBar))}"/>
</map>
</property>
</bean>]]></programlisting>
<para>
This factory bean definition will override the default <code>integrationEvaluationContext</code>
bean definition, adding the custom accessor to the list (which also includes the standard
accessors mentioned above), and one custom function.
</para>
<para>
Note that custom functions are static methods.
In the above example, the custom function is a static method <code>calc</code> on class
<classname>MyFunctions</classname> and takes a single parameter of type <classname>MyBar</classname>.
</para>
<para>
Say you have a <classname>Message</classname> with a payload that has a type <classname>MyFoo</classname>
on which you need to perform some action to create a <classname>MyBar</classname> object from it,
and you then want to invoke a custom function <code>calc</code> on that object.
</para>
<para>
The standard property accessors wouldn't know how to get a <classname>MyBar</classname>
from a <classname>MyFoo</classname> so you could write
and configure a custom property accessor to do so. So, your final expression might be
<code>"#barcalc(payload.myBar)"</code>.
</para>
</section>
</appendix>

8
src/reference/docbook/whats-new.xml
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@@ -68,6 +68,14 @@
<xref linkend="file-tailing"/>.
</para>
</section>
<section id="3.0-spel-customization">
<title>Spring Expression Language (SpEL) Configuration</title>
<para>
A new factory bean is provided to allow
configuration of custom <interfacename>PropertyAccessor</interfacename>s and functions for
use in SpEL expressions throughout the framework. For more information see <xref linkend="spel" />.
</para>
</section>
</section>
<section id="3.0-general">

4
src/reference/docbook/xmpp.xml
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@@ -201,8 +201,8 @@ xsi:schemaLocation="http://www.springframework.org/schema/integration/xmpp
</note>
</para>
</section>
<section id="xmpp-appendices">
<title>Appendices</title>
<section id="xmpp-advanced">
<title>Advanced Configuration</title>
<para>
Since Spring Integration XMPP support is based on the Smack 3.1 API (http://www.igniterealtime.org/downloads/index.jsp), it is important