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INT-3306 Document Release Strategy POJO Limitation

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JIRA: https://jira.springsource.org/browse/INT-3306

Add a caution about using POJO ReleaseStrategy with large groups.
This commit is contained in:
Gary Russell
2014-02-24 17:34:40 -05:00
committed by Artem Bilan
parent 00a4bc8cc7
commit 233aaffb3b
1 changed files with 16 additions and 1 deletions
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17
src/reference/docbook/aggregator.xml
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@@ -256,7 +256,22 @@ anything other than <classname>Message</classname>). Typically this would satisf
for some reason, you need to access the full <classname>MessageGroup</classname>
then you should simply provide an implementation of the <classname>ReleaseStrategy</classname> interface.
</para>
<caution>
<para>
When handling potentially large groups, it is important to understand how these methods are invoked because the release
strategy may be invoked multiple times before the group is released. The most efficient is an implementation of
<interfacename>ReleaseStrategy</interfacename> because the aggregator can invoke it directly. The second most
efficient is a POJO method with a <code>Collection&lt;Message&lt;?&gt;&gt;</code> parameter type. The least efficient
is a POJO method with a <code>Collection&lt;Foo&gt;</code> type - the framework has to copy the payloads from the messages
in the group into a new collection (and possibly attempt conversion on the payloads to <code>Foo</code>) every time the
release strategy is called. <code>Collection&lt;?&gt;</code> avoids the conversion but still requires creating the
new <interfacename>Collection</interfacename>.
</para>
<para>
<emphasis role="bold">For these reasons, for large groups, it is recommended that you implement
<interfacename>ReleaseStrategy</interfacename>.</emphasis>
</para>
</caution>
<para>When the group is released for aggregation, all its not-yet-released
messages are processed and removed from the group.
If the group is also complete (i.e. if all messages from a