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INT-1691 updated FTP documentation with poller configuration notes

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Oleg Zhurakousky
2010-12-16 13:24:18 -05:00
parent a6cf3b74bb
commit f7beff8d11
1 changed files with 31 additions and 1 deletions
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docs/src/reference/docbook/ftp.xml
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@@ -162,6 +162,36 @@ xsi:schemaLocation="http://www.springframework.org/schema/integration/ftp
<bean id="customFilter" class="org.example.CustomFilter"/>
]]></programlisting>
</para>
<para>
<emphasis>Poller configuration notes for FTP Inbound adapter</emphasis>
</para>
<para>
The job of protocol specific adapters such as FTP consists of two tasks.
<emphasis>1) Communicate with remote server and transfer file from the remote directory to the local directory</emphasis>
<emphasis>2) Generate Message with the transferred file as a payload and send it to a channel identified via 'channel' attribute.</emphasis>
That is why they called 'channel-adapters' not just 'adapters' and therefore the main job of such adapter is to generate a
Message which essentially makes the second part of the above explanation to take precedence in such way that
*IF* your local directory already has a file(s) it will first generate Messages from these files and *ONLY*
when all files have been processed it will initiate the remote communication to get more files.
So when configuring a trigger on the poller you might want to pay an extra attention to <code>max-messages-per-poll</code>
attribute which has a default value of 1 for all <classname>SourcePollingChannelAdapter</classname> instances (e.g., FTP).
This means that as soon as one file is processed it will wait for the next execution time which is dependent on your
trigger configuration, so if you happened to have a file(s) sitting in the <code>local-directory</code> it would process
those files before it would initiate communication with remote FTP server and if the <code>max-messages-per-poll</code>
was set to 1 (default) then it would be processing one file at the time with intervals defined by your trigger
essentially working as <emphasis>one-poll = one-file</emphasis>.
</para>
<para>
For typical use cases you most likely want the oposite behavior and that is to process all the files you can for each
poll and only then wait for the next poll. If that is the case it is recommended to set <code>max-messages-per-poll</code> to -1
value which means on each poll the adapter will attempt to generate as many messages as it possibly can meaning it will process
everything in the local directory, then it will connect to the remote directory transferring everything that is available
there and processing them locally. Only then the poll will stop and wait for the next execution time
You can also set it to some value greater then 1 (e.g., 10 which means on each poll attempt to process no more then 10 files)
</para>
</section>
<section id="ftp-outbound">
@@ -202,6 +232,6 @@ xsi:schemaLocation="http://www.springframework.org/schema/integration/ftp
instead of remote-directory="/foo/bar")
</important>
</para>
</section>
</chapter>