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INT-1501 enhanced documentation to include examples and explanation on header enricher sub-element including SpEL support

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Oleg Zhurakousky
2010-11-10 12:10:19 -05:00
parent 30e106eeb0
commit 3066911916
1 changed files with 66 additions and 6 deletions
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72
docs/src/reference/docbook/content-enrichment.xml
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@@ -16,13 +16,73 @@
<title>Header Enricher</title>
<para>
If you only need to add headers to a Message, and they are not dynamically determined by Message content,
then referencing a custom implementation may be overkill. For that reason, Spring Integration provides the
'header-enricher' element. <programlisting language="xml"><![CDATA[ <header-enricher input-channel="in" output-channel="out">
<header name="foo" value="123"/>
<header name="bar" ref="someBean"/>
</header-enricher>]]></programlisting>
If you only need to add headers to a Message, and they are not dynamically determined by the Message content,
then referencing a custom implementation of the Transformer may be an overkill. For that reason,
Spring Integration provides the <emphasis>Header Enricher</emphasis> which is exposed via <code>&lt;header-enricher&gt;</code> element.
<programlisting language="xml"><![CDATA[<int:header-enricher input-channel="in" output-channel="out">
<int:header name="foo" value="123"/>
<int:header name="bar" ref="someBean"/>
</int:header-enricher>]]></programlisting>
</para>
<para>
<emphasis>Header Enricher</emphasis> also provides helpful sub-elements to set well known header names.
<programlisting language="xml"><![CDATA[<int:header-enricher input-channel="in" output-channel="out">
<int:error-channel ref="applicationErrorChannel"/>
<int:reply-channel ref="quoteReplyChannel"/>
<int:correlation-id value="123"/>
<int:priority value="HIGHEST"/>
<int:header name="bar" ref="someBean"/>
</int:header-enricher>]]></programlisting>
In the above configuration you can clearly see that for well known headers such as <code>errorChannel</code>,
<code>correlationId</code>, <code>priority</code>, <code>replyChannel</code>etc., instead of using generic <emphasis>&lt;header&gt;</emphasis>
sub-element where you would have to provide both header 'name' and 'value', you can use convenient sub-elements
allowing you to set those values directly.
</para>
<para>
<emphasis>SpEL Support</emphasis>
</para>
<para>
In Spring Integration 2.0 we are introducing convenience of
<link href="http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/expressions.html">Spring Expression Language (SpEL)</link>
to help configure many different components. <emphasis>Header Enricher</emphasis> is one of them.
A lot of times, header value cannot be defined statically and has to be computed dynamically. That is why
<emphasis>Header Enricher</emphasis> allows you to also specify bean 'ref' and 'method' that will calculate the
header value. Let's look at the following configuration:
<programlisting language="xml"><![CDATA[<int:header-enricher input-channel="in" output-channel="out">
<int:header name="foo" method="computeValue" ref="myBean"/>
</int:header-enricher>
<bean id="myBean" class="foo.bar.MyBean"/>]]></programlisting>
<programlisting language="java"><![CDATA[public class MyBean{
public String computeValue(String payload){
return payload.toUpperCase() + "_US";
}
}]]></programlisting>
As you can see that the computation logic to determine the header value is actually pretty simple and the
natural question would be is there a simpler way to accomplish this? And that is where SpEL shows its true power.
<programlisting language="xml"><![CDATA[<int:header-enricher input-channel="in" output-channel="out">
<int:header name="foo" expression="payload.toUpperCase() + '_US'"/>
</int:header-enricher>]]></programlisting>
As you can see, with SpEL for simple cases like above we no longer have to provide a separate class and configure
it in the application context. All we need is to use <emphasis>expression</emphasis> attribute and provide a valid
SpEL expression. You can also see that 'payload' and 'headers' are bound as variables to the SpEL Evaluation Context
giving you full access to the incoming Message.
</para>
<para>
<emphasis>Adapter specific Header Enrichers</emphasis>
</para>
<para>
As you go through the manual you will see that as an added convenience
Spring Integration provides adapter specific Header Enrichers (e.g., WS, XMPP, etc.)
</para>
</section>
</section>