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INT-1731 updated transformer documentation to reflect the change related to 'transformer must never return null'

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Oleg Zhurakousky
2011-01-06 14:32:31 -05:00
parent 8bd6f2fb37
commit 7288315528
1 changed files with 11 additions and 4 deletions
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docs/src/reference/docbook/transformer.xml
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@@ -60,13 +60,20 @@
<para>
The method that is used for transformation may expect either the <interfacename>Message</interfacename> type or
the payload type of inbound Messages. It may also accept Message header values either individually or as a full
map by using the @Header and @Headers parameter annotations respectively. The return value of the method can be
map by using the <code>@Header</code> and <code>@Headers</code> parameter annotations respectively. The return value of the method can be
any type. If the return value is itself a <interfacename>Message</interfacename>, that will be passed along to
the transformer's output channel. If the return type is a Map, and the original Message payload was
<emphasis>not</emphasis> a Map, the entries in that Map will be added to the Message headers of the original
Message (the keys must be Strings). If the return value is <emphasis>null</emphasis>, then no reply Message will
be sent (effectively the same behavior as a Message Filter returning false). Otherwise, the return value will be
sent as the payload of an outbound reply Message.
Message (the keys must be Strings).
</para>
<para>
Since Spring Integration 2.0 after many debates we've changed the behavior of Message Transformer for the cases where
transformation method returns <code>null</code>. Returning <code>null</code> will now result in the exception. In other
words Message Transformer should no longer be used as Message Filter (that is what Message Filter is for). Message Transformer
should always be expected to transform the source Message into a valid target Message.
However, if you still need this type of behavior (where component might return NULL and not be considered an error), a
<emphasis>service-activator</emphasis> could be used. Its <code>requires-reply</code> value is FALSE by default, but can
be set to TRUE in order to have Exceptions thrown for NULL return values.
</para>
<para>