45 lines
2.8 KiB
XML
45 lines
2.8 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<chapter id="service-activator">
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<title>Service Activator</title>
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<section id="service-activator-introduction">
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<title>Introduction</title>
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<para>
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The Service Activator is the endpoint type for connecting any Spring-managed Object to an input channel so that
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it may play the role of a service. If the service produces output, it may also be connected to an output channel.
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Alternatively, an output producing service may be located at the end of a processing pipeline or message flow in
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which case, the inbound Message's "replyChannel" header can be used. This is the default behavior if no output
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channel is defined, and as with most of the configuration options you'll see here, the same behavior actually
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applies for most of the other components we have seen.
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</para>
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</section>
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<section id="service-activator-namespace">
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<title>The <service-activator/> Element</title>
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<para>
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To create a Service Activator, use the 'service-activator' element with the 'input-channel' and 'ref' attributes:
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<programlisting language="xml"><service-activator input-channel="exampleChannel" ref="exampleHandler"/></programlisting>
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</para>
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<para>
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The configuration above assumes that "exampleHandler" either contains a single method annotated with the
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@ServiceActivator annotation or that it contains only one public method at all. To delegate to an explicitly
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defined method of any object, simply add the "method" attribute.
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<programlisting language="xml"><service-activator input-channel="exampleChannel" ref="somePojo" method="someMethod"/></programlisting>
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</para>
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<para>
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In either case, when the service method returns a non-null value, the endpoint will attempt to send the reply
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message to an appropriate reply channel. To determine the reply channel, it will first check if an
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"output-channel" was provided in the endpoint configuration:
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<programlisting language="xml"><service-activator input-channel="exampleChannel" output-channel="replyChannel"
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ref="somePojo" method="someMethod"/></programlisting>
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If no "output-channel" is available, it will then check the Message's <literal>RETURN_ADDRESS</literal> header
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value. If that value is available, it will then check its type. If it is a
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<interfacename>MessageChannel</interfacename>, the reply message will be sent to that channel. If it is a
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<classname>String</classname>, then the endpoint will attempt to resolve the channel name to a channel instance.
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If the channel cannot be resolved, then a <classname>ChannelResolutionException</classname> will be thrown.
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</para>
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</section>
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</chapter> |