dc1d1868d9
INT-2425 - Poller: Document the Ability to Change Polling Rate at Runtime For reference see: * https://jira.springsource.org/browse/INT-2430 * https://jira.springsource.org/browse/INT-2425 INT-2430 - Code Review - Minor spelling error fix in src/reference/docbook/endpoint.xml INT-2430 - Code Review - Doc updates * Add more documentation around the dynamic poller sample * Standardize Endpoint chapter so that for emphasis of properties the <emphasis/> docbook element is used rather than quotes. Polishing
72 lines
4.5 KiB
XML
72 lines
4.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<section xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="polling-consumer"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Poller (Polling Consumer)</title>
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<para>
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When Message Endpoints (Channel Adapters) are connected to channels and
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instantiated, they produce one of the following 2 instances:
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</para>
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<itemizedlist>
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<listitem><ulink url="http://static.springsource.org/spring-integration/api/org/springframework/integration/endpoint/PollingConsumer.html">PollingConsumer</ulink></listitem>
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<listitem><ulink url="http://static.springsource.org/spring-integration/api/org/springframework/integration/endpoint/EventDrivenConsumer.html">EventDrivenConsumer</ulink></listitem>
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</itemizedlist>
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<para>
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The actual implementation depends on which type of channel these Endpoints
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are connected to. A channel adapter connected to a channel that implements
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the <interfacename><ulink url="http://static.springsource.org/spring-integration/api/org/springframework/integration/core/SubscribableChannel.html">org.springframework.integration.core.SubscribableChannel</ulink></interfacename>
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interface will produce an instance of <classname>EventDrivenConsumer</classname>.
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On the other hand, a channel adapter connected to a channel that implements the
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<interfacename><ulink url="http://static.springsource.org/spring-integration/api/org/springframework/integration/core/PollableChannel.html">org.springframework.integration.core.PollableChannel</ulink></interfacename>
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interface (e.g. a QueueChannel) will produce an instance of <classname>PollingConsumer</classname>.
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</para>
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<para>
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Polling Consumers allow Spring Integration components to actively poll for
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Messages, rather than to process Messages in an event-driven manner.
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</para>
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<para>
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They represent a critical cross cutting concern in many
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messaging scenarios. In Spring Integration, Polling Consumers are based
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on the pattern with the same name, which is described in the book
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"Enterprise Integration Patterns" by Gregor Hohpe and Bobby Woolf. You
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can find a description of the pattern on the book's website at:
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</para>
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<itemizedlist>
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<listitem><ulink url="http://www.enterpriseintegrationpatterns.com/PollingConsumer.html">
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http://www.enterpriseintegrationpatterns.com/PollingConsumer.html
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</ulink></listitem>
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</itemizedlist>
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<para>
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Furthermore, in Spring Integration a second variation of the Polling Consumer
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pattern exists. When Inbound Channel Adapters are being used, these adapters
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are often wrapped by a <classname>SourcePollingChannelAdapter</classname>.
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For example, when retrieving messages from a remote FTP Server location,
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the adapter described in <xref linkend="ftp-inbound" />
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is configured with a <emphasis>poller</emphasis> to retrieve messages periodically.
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So, when components are configured with Pollers, the resulting instances are
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of one of the following types:
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</para>
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<itemizedlist>
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<listitem><ulink url="http://static.springsource.org/spring-integration/api/org/springframework/integration/endpoint/PollingConsumer.html">PollingConsumer</ulink></listitem>
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<listitem><ulink url="http://static.springsource.org/spring-integration/api/org/springframework/integration/endpoint/SourcePollingChannelAdapter.html">SourcePollingChannelAdapter</ulink></listitem>
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</itemizedlist>
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<para>
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This means, Pollers are used in both inbound and outbound messaging scenarios.
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Here are some use-cases that illustrate the scenarios in which Pollers are
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used:
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</para>
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<itemizedlist>
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<listitem>Polling certain external systems such as FTP Servers, Databases, Web Services</listitem>
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<listitem>Polling internal (pollable) Message Channels</listitem>
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<listitem>Polling internal services (E.g. repeatedly execute methods on a Java class)</listitem>
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</itemizedlist>
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<para>
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This chapter is meant to only give a high-level overview regarding Polling Consumers
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and how they fit into the concept of message channels - <xref linkend="channel"/> and
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channel adapters -
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<xref linkend="channel-adapter"/>. For more in-depth information regarding
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Messaging Endpoints in general and Polling Consumers in particular, please see
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<xref linkend="endpoint"/>.
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</para>
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</section>
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