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This commit is contained in:
Mark Fisher
2009-07-03 16:23:38 +00:00
parent 16fde0a821
commit 46716aca17
1 changed files with 24 additions and 14 deletions
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spring-integration-reference/src/chain.xml
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@@ -27,18 +27,25 @@
</para>
<para>
The handler chain simplifies configuration while internally maintaining the same degree of loose coupling between
components, and it is trivial to modify the configuration if at some point a non-linear arrangement is required.
The chain will be expanded into a linear setup of the listed endpoints, separated by direct
channels. The reply channel header will not be taken into account within the chain: only
after the last handler is invoked will the resulting message be forwarded onto the reply channel or the chain's output
channel. Because of this setup all handlers except the last require a <methodname>setOutputChannel</methodname>
implementation. The last handler only needs an output channel if the outputChannel on the MessageHandlerChain is set.
If this is not the case, the "replyChannel" header needs to be set on each message, so that it is clear where the
message needs to go.
components, and it is trivial to modify the configuration if at some point a non-linear arrangement is required.
</para>
<para>
Internally, the chain will be expanded into a linear setup of the listed endpoints, separated by direct channels.
The reply channel header will not be taken into account within the chain: only after the last handler is invoked
will the resulting message be forwarded on to the reply channel or the chain's output channel. Because of this
setup all handlers except the last require a <methodname>setOutputChannel</methodname> implementation. The last
handler only needs an output channel if the outputChannel on the MessageHandlerChain is set.
<note>
<para>
As with other endpoints, the output-channel is optional. If there is a reply Message at the end of the
chain, the output-channel takes precedence, but if not available, the chain handler will check for a
reply channel header on the inbound Message.
</para>
</note>
</para>
<para>
In most cases there is no need to implement MessageHandlers yourself. The next section will focus on namespace
support for the chain element. Most Spring Integration enpoints like Service Activators and Transformers are
support for the chain element. Most Spring Integration endpoints, like Service Activators and Transformers, are
suitable for use within a <classname>MessageHandlerChain</classname>.
</para>
</section>
@@ -47,8 +54,8 @@
<title>The &lt;chain&gt; Element</title>
<para>
The &lt;chain&gt; element provides an 'input-channel' attribute, and if the last element in the chain is capable
of producing reply messages, it may optionally provide an 'output-channel' attribute. The sub-elements are then
filters, transformers, splitters, and service-activators. The last element may also be a router or aggregator.
of producing reply messages (optional), it also supports an 'output-channel' attribute. The sub-elements are then
filters, transformers, splitters, and service-activators. The last element may also be a router.
<programlisting language="xml"><![CDATA[ <chain input-channel="input" output-channel="output">
<filter ref="someSelector" throw-exception-on-rejection="true"/>
<header-enricher error-channel="customErrorChannel">
@@ -57,9 +64,12 @@
<service-activator ref="someService" method="someMethod"/>
</chain>]]></programlisting>
</para>
The &lt;header-enricher&gt; element used in the above example will set a message header with name "foo" and value "bar" on the message.
A header enricher is a specialization of Transformer that touches only header values. You could obtain the same result by
implementing a MessageHandler that did the header modifications and wiring that as a bean.
<para>
The &lt;header-enricher&gt; element used in the above example will set a message header with name "foo" and
value "bar" on the message. A header enricher is a specialization of Transformer that touches only header
values. You could obtain the same result by implementing a MessageHandler that did the header modifications
and wiring that as a bean.
</para>
</section>
</chapter>