83cac18b6e
* incremental progress on getting docbkx working - downgraded docbook 4.5 -> 4.4 because of "URI is not file" errors (`find src/docbkx/*.xml | xargs grep -l '4\.5' | xargs perl -p -i -e 's/4\.5/4.4/g'`) - eliminated spring-integration-reference in favor of idiomatic src/docbkx under project root - using xsl from spring-ws to get things working. need to figure out how to integrate previous xsl, however (it's still there), because the L&F is quite different now - upgraded version of docbkx plugin to 2.0.9
62 lines
4.0 KiB
XML
62 lines
4.0 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<chapter id="delayer">
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<title>Delayer</title>
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<section id="delayer-introduction">
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<title>Introduction</title>
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<para>
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A Delayer is a simple endpoint that allows a Message flow to be delayed by a certain interval. When
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a Message is delayed, the original sender will not block. Instead, the delayed Messages will be
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scheduled with an instance of <interfacename>java.util.concurrent.ScheduledExecutorService</interfacename>
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to be sent to the output channel after the delay has passed. This approach is scalable even for
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rather long delays, since it does not result in a large number of blocked sender Threads. On the
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contrary, in the typical case a thread pool will be used for the actual execution of releasing the
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Messages. Below you will find several examples of configuring a Delayer.
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</para>
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</section>
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<section id="delayer-namespace">
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<title>The <delayer> Element</title>
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<para>
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The <delayer> element is used to delay the Message flow between two Message Channels.
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As with the other endpoints, you can provide the "input-channel" and "output-channel" attributes,
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but the delayer also requires at least the 'default-delay' attribute with the number of milliseconds
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that each Message should be delayed.
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<programlisting language="xml"><![CDATA[ <delayer input-channel="input" default-delay="3000" output-channel="output"/>]]></programlisting>
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If you need per-Message determination of the delay, then you can also provide the name of a header
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within the 'delay-header-name' attribute:
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<programlisting language="xml"><![CDATA[ <delayer input-channel="input" output-channel="output"
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default-delay="3000" delay-header-name="delay"/>]]></programlisting>
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In the example above the 3 second delay would only apply in the case that the header value is
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not present for a given inbound Message. If you only want to apply a delay to Messages that have
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an explicit header value, then you can set the 'default-delay' to 0. For any Message that has a
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delay of 0 (or less), the Message will be sent directly. In fact, if there is not a positive delay
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value for a Message, it will be sent to the output channel on the calling Thread.
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<tip>
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The delay handler actually supports header values that represent an interval in milliseconds (any
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Object whose <methodname>toString()</methodname> method produces a value that can be parsed into a
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Long) as well as <classname>java.util.Date</classname> instances representing an absolute time.
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In the former case, the milliseconds will be counted from the current time (e.g. a value of 5000
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would delay the Message for at least 5 seconds from the time it is received by the Delayer). In
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the latter case, with an actual Date instance, the Message will not be released until that Date
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occurs. In either case, a value that equates to a non-positive delay, or a Date in the past, will
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not result in any delay. Instead, it will be sent directly to the output channel in the original
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sender's Thread.
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</tip>
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</para>
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<para>
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The delayer delegates to an instance of Spring's <interfacename>TaskScheduler</interfacename> abstraction.
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The default scheduler is a <classname>ThreadPoolTaskScheduler</classname> instance with a pool size of 1.
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If you want to delegate to a different scheduler, you can provide a reference through the delayer element's
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'scheduler' attribute:
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<programlisting language="xml"><![CDATA[ <delayer input-channel="input" output-channel="output"
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default-delay="0" delay-header-name="delay"
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scheduler="exampleTaskScheduler"/>
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<task:scheduler id="exampleTaskScheduler" pool-size="3"/>]]></programlisting>
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</para>
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</section>
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</chapter> |