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INT-1516 added docs for aggregator ans SpEL

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This commit is contained in:
Oleg Zhurakousky
2010-11-12 09:27:49 -05:00
parent ba665734fb
commit 858570882e
1 changed files with 38 additions and 1 deletions
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39
docs/src/reference/docbook/aggregator.xml
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@@ -323,7 +323,8 @@
id="aggxmlCorrelationStrategyMethod" /><![CDATA[
message-store="messageStore" ]]><co id="aggxml11-co" linkends="aggxml11" /><![CDATA[
send-partial-result-on-expiry="true" ]]><co id="aggxml9" /><![CDATA[
send-timeout="86420000" ]]><co id="aggxml10" /><![CDATA[ />
send-timeout="86420000" ]]><co id="aggxml10" /><![CDATA[
expression="#this.toArray()" ]]><co id="aggxml12" /><![CDATA[/>
<channel id="outputChannel"/>
@@ -420,6 +421,10 @@
<para>The timeout for sending the aggregated messages to the output or
reply channel. <emphasis>Optional</emphasis>.</para>
</callout>
<callout arearefs="aggxml12">
<para>SpEL expression to handle release strategy <emphasis>Optional</emphasis>.</para>
</callout>
</calloutlist>
<para>Using a "ref" attribute is generally recommended if a custom
@@ -492,6 +497,38 @@
strategy method and the aggregator method can be combined in a single
bean (all of them or any two).</para>
</note>
<para>
<emphasis>Aggregators and Spring Expression Language (SpEL)</emphasis>
</para>
<para>
Since Spring Integration 2.0, the <emphasis>release strategy</emphasis> may be handled with SpEL (http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/expressions.html)
which would be recommend if the logic behind such <emphasis>release strategy</emphasis> is relatively simple.
Let's say you have a legacy component which was designed to receive an array of objects. We know that default release
strategy will assemble all aggregated messages in the List. So now we have two problems. First we need to extract individual
messages form such list, extract payload of each message and assemble them into the array of objects (see code below)
<programlisting language="java"><![CDATA[public String[] processRelease(List<Message<String>> mesages){
List<String> strList = new ArrayList<String>();
for (Message<String> message : mesages) {
strList.add(message.getPayload());
}
return strList.toArray(new String[]{});
}]]></programlisting>
However, with SpEL such requirement could actually be handled relatively easy with a simple
one-line expression, thus sparing you from writing a custom class and configuring it as a bean.
<programlisting language="xml"><![CDATA[<int:aggregator input-channel="aggrChannel"
output-channel="replyChannel"
expression="#this.![payload].toArray()"/>]]></programlisting>
In the above configuration we are using <emphasis>Collection Projection</emphasis> expression
(http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/expressions.html#d0e12113) to
assemble a new collection from the payloads of all messages in the list and then transforming it to an Array, thus
achieving the same result as the java code above.
</para>
</section>
<section>