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clarified the documentation about providing a message-store for a QueueChannel

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Mark Fisher
2011-02-05 19:41:28 -05:00
parent d7e7fd7348
commit 6325e42588
1 changed files with 25 additions and 36 deletions
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docs/src/reference/docbook/channel.xml
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@@ -438,58 +438,47 @@ public Message<?> receive(final PollableChannel<?> channel) { ... }]]></programl
<para><emphasis>Persistent QueueChannel Configuration</emphasis></para>
<para>
Since <classname>QueueChannel</classname> provides capability to buffer Messages it also introduces a point of failure
where Messages could be lost in the event of the system crash. To mitigate this risk, <classname>QueueChannel</classname> is
backed by a persistent store which is exposed via simple strategy interface <classname>MessageStore</classname>:
<programlisting language="java"><![CDATA[public interface MessageStore {
Message<?> getMessage(UUID id);
<T> Message<T> addMessage(Message<T> message);
Message<?> removeMessage(UUID id);
int getMessageCount();
}]]></programlisting>
For more details on <classname>MessageStore</classname> see <xref linkend="message-store" />.
Since a <classname>QueueChannel</classname> provides the capability to buffer Messages, but does so in-memory only
by default, it also introduces a possibility that Messages could be lost in the event of a system failure. To
mitigate this risk, a <classname>QueueChannel</classname> may be backed by a persistent implementation of the
<classname>MessageGroupStore</classname> strategy interface. For more details on <classname>MessageGroupStore</classname>
and <classname>MessageStore</classname> see <xref linkend="message-store" />.
</para>
<para>
When <classname>QueueChannel</classname> receives the Message it will add the Message to the <classname>MessageStore</classname>
by invoking <code>addMessage(Message)</code> method and when the Message is polled from the <classname>MessageStore</classname>
it is removed from it via <code>removeMessage(UUID)</code> method.
When a <classname>QueueChannel</classname> receives a Message, it will add it to the Message Store, and when a Message
is polled from a <classname>QueueChannel</classname>, it is removed from the Message Store.
</para>
<para>
By default any <classname>QueueChannel</classname> is bootstrapped with <classname>SimpleMessageStore</classname> which is
in-memory Map-based implementation of the <classname>MessageStore</classname> interface. However Spring Integration
also provides <classname>JdbcMessageStore</classname> to allow <classname>QueueChannel</classname> to be backed by an RDBMS.
By default any <classname>QueueChannel</classname> only stores its Messages in an in-memory Queue
and can therefore lead to the lost message scenario mentioned above. However Spring Integration
provides a <classname>JdbcMessageStore</classname> to allow a <classname>QueueChannel</classname> to be backed by an RDBMS.
</para>
<para>
You configure <classname>MessageStore</classname> for <classname>QueueChannel</classname> via <code>message-store</code> attribute.
You can configure a Message Store for any <classname>QueueChannel</classname> by adding the
<code>message-store</code> attribute as shown in the next example.
<programlisting language="xml"><![CDATA[<int:channel id="myChannel">
<int:queuel message-store="messageStore">
<programlisting language="xml"><![CDATA[<int:channel id="dbBackedChannel">
<int:queue message-store="messageStore">
<int:channel id="myChannel">
<jdbc:embedded-database id="dataSource" type="HSQL"/>
<int-jdbc:message-store id="messageStore" data-source="dataSource"/>]]></programlisting>
<int-jdbc:message-store id="messageStore" data-source="someDataSource"/>]]></programlisting>
You can also see that you can configure <classname>JdbcMessageStore</classname> via namespace support provided by
Spring Integration JDBC module. All you need to do is inject any standard Spring datasource. Spring Integration JDBC
module also provides schemas for most popular databases. These schemas are located in
<emphasis>org.springframework.integration.jdbc</emphasis> package of Spring Integration JDBC module.
The above example also shows that <classname>JdbcMessageStore</classname> can be configured with the namespace support
provided by the Spring Integration JDBC module. All you need to do is inject any <classname>javax.sql.DataSource</classname>
instance. The Spring Integration JDBC module also provides schema DDL for most popular databases. These schemas are located in
the <emphasis>org.springframework.integration.jdbc</emphasis> package of that module (spring-integration-jdbc).
<important>
One thing to remember is that with any transactional persistent store (e.g., JdbcMessageStore)
the messages removed from such persistent store will only be completely removed if transaction completed
successfully, otherwise transaction will roll back and the Message will not be lost.
One thing to remember is that with any transactional persistent store (e.g., JdbcMessageStore),
a Message removed from the store will only be permanently removed if the transaction completes
successfully, otherwise the transaction will roll back and the Message will not be lost.
</important>
And of course you can alway provide your own implementation of MessageStore interface
Many other implementations of the Message Store will be available as the growing number of Spring projects
related to "NoSQL" data stores provide the underlying support. Of course, you can always provide your own implementation
of the MessageGroupStore interface if you cannot find one that meets your particular needs.
</para>
</section>
<section id="channel-configuration-pubsubchannel">
<title>PublishSubscribeChannel Configuration</title>
<para>