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This is a significant update to the build system, including the changes listed below. README.md has been updated with instructions on the most important day-to-day commands. - Eliminate buildSrc submodule In favor of using the new bundlor and docbook-reference plugins. The net effect is a large reduction in number of lines of build code. Common docbook resources, stylesheets, etc are stored directly in the docbook plugin. This means that --recursive is no longer required when cloning and there will never be a need to use `git submodule` commands. README files have been updated to reflect. Use of the new bundlor plugin also means the removal of template.mf files from the source tree in favor of an inline approach. See build.gradle for details. Bundlor 'import templates' are built up programmatically and kept physically close to gradle dependency declarations, leading to more convenience when changing these values and hopefully fewer errors / version inconsistencies over time. Certain tests depended on the presence of template.mf files, all of which have recently been removed from the source tree in favor of the new bundlor plugin which allows for inlining bundlor configuration within the Gradle build script. These tests now create temp files using the java.io.File API instead. - Upgrade to Gradle 1.0-milestone-6 The m6 release is significantly faster when resolving dependencies and has a number of valuable new features over the earlier m3 version. Review the release notes for Gradle 1.0-milestone-6 online for full details. - Switch to repo.springsource.org repository Previously the project build declared as many repositories as necessary to resolve all project dependencies. Now depending on a single 'virtual repository' defined within the SpringSource Artifactory instance at http://repo.springsource.org. Currently, the virtual repository in use is 'libs-milestone', which allows for the resolution of all "milestone-or-better" versions of all S2 and third-party dependencies. Should snapshot dependencies become required, this value may be changed from 'libs-milestone' to 'libs-snapshot'. To build only against GA releases, change the value to 'libs-release'. - New build plan(s) Spring Integration build plans have been updated to use the Artifactory Bamboo plugin and publish to repo.springsource.org. Build plans have names like 2.1.x to reflect the version under development, not necessarily the name of the branch, as this may change over time and across major releases. - Improve release process As mentioned above, Spring Integration will now use the Artifactory Bamboo plugin to publish releases and also use Artifactory's support for pushing builds directly into Maven Central via oss.sonatype.org. Generate poms that contain all necessary fields for onboarding at Maven central (scm, developers, organization, licenses, etc). Generate -source and -javadoc poms to comply with Maven Central onboarding rules (and for general good practice anyway). Generation of PGP signatures, sha1 and md5 checksums are all handled automatically by Artifactory. These are also requirements for automated entry into Maven Central. - Remove source-level pom generation Automatic generation of Maven poms suitable for use in building Spring Integration is no longer supported. Generation and publication of poms for the purpose of dependency management remains supported. Sonar support has to date depended on these poms, but will be switched over to use the Gradle Sonar plugin shortly. - Eliminate docs subproject Move docs/src to the root of the project and eliminate docs as a formal subproject. This simplifies the build in a number of ways, including removing the need for distinguishing between 'subprojects' and 'javaprojects' as well as allowing users to build both 'api' and 'reference' docs without qualifying with a ':docs' prefix. Also rename the src/info directory to src/dist to better reflect that these files are packaged with the distribution. For example, the readme.txt there is really the distribution readme, distinct from the README.md at the root of the project which is for building from source, etc.
98 lines
6.5 KiB
XML
98 lines
6.5 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="message-store"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Message Store</title>
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<para>
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Enterprise Integration Patterns (EIP) identifies several patterns that have the capability to buffer messages. For example,
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an <emphasis>Aggregator</emphasis> buffers messages until they can be released and a <emphasis>QueueChannel</emphasis> buffers
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messages until consumers explicitly receive those messages from that channel.
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Because of the failures that can occur at any point within your message flow, EIP components that buffer
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messages also introduce a point where messages could be lost.
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</para>
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<para>
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To mitigate the risk of losing Messages, EIP defines the <ulink url="http://eaipatterns.com/MessageStore.html">Message Store</ulink> pattern which allows
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EIP components to store <emphasis>Messages</emphasis> typically in some type of persistent store (e.g. RDBMS).
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</para>
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<para>
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Spring Integration provides support for the <emphasis>Message Store</emphasis> pattern by
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a) defining a <classname>org.springframework.integration.store.MessageStore</classname> strategy interface,
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b) providing several implementations of this interface, and
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c) exposing a <code>message-store</code> attribute on all components that have the capability to buffer messages
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so that you can inject any instance that implements the <classname>MessageStore</classname> interface.
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</para>
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<para>Details on how to configure a specific <emphasis>Message Store</emphasis> implementation and/or how to inject
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a <classname>MessageStore</classname> implementation into a specific buffering component are described
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throughout the manual (see the specific component, such as <emphasis>QueueChannel</emphasis>, <emphasis>Aggregator</emphasis>,
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<emphasis>Resequencer</emphasis> etc.), but here are a couple of samples to give you an idea:
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</para>
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<para>
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QueueChannel
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<programlisting language="xml"><![CDATA[<int:channel id="myQueueChannel">
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<int:queue message-store="refToMessageStore"/>
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<int:channel>]]></programlisting>
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</para>
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<para>
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Aggregator
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<programlisting language="xml"><![CDATA[<int:aggregator . . . message-store="refToMessageStore"/>]]></programlisting>
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</para>
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<para>
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By default <emphasis>Messages</emphasis> are stored in-memory using <classname>org.springframework.integration.store.SimpleMessageStore</classname>,
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an implementation of <classname>MessageStore</classname>. That might be fine for development or simple low-volume environments where the potential loss
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of non-persistent messages is not a concern. However, the typical production application will need a more robust option, not only to mitigate the risk of
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message loss but also to avoid potential out-of-memory errors. Therefore, we also provide MessageStore implementations for a variety of data-stores.
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Below is a complete list of supported implementations:
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<itemizedlist>
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<listitem><xref linkend="jdbc-message-store"/> - uses RDBMS to store Messages</listitem>
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<listitem><xref linkend="redis-message-store"/> - uses Redis key/value datastore to store Messages</listitem>
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<listitem><xref linkend="mongodb-message-store"/> - uses MongoDB document store to store Messages</listitem>
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<listitem><xref linkend="gemfire-message-store"/> - uses Gemfire distributed cache to store Messages</listitem>
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</itemizedlist>
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</para>
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<para>
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<important>
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<para>However be aware of some limitations while using persistent implementations of the <classname>MessageStore</classname>.</para>
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<para>The Message data (payload and headers) is <emphasis>serialized</emphasis> and <emphasis>deserialized</emphasis>
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using different serialization strategies depending on the implementation of the <classname>MessageStore</classname>.
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For example, when using <classname>JdbcMessageStore</classname>, only <classname>Serializable</classname> data is persisted by default.
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In this case non-Serializable headers are removed before serialization occurs.
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Also be aware of the protocol specific headers that are injected by transport adapters (e.g., FTP, HTTP, JMS etc.).
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For example, <literal><http:inbound-channel-adapter/></literal> maps HTTP-headers into Message Headers and one of them is an
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<classname>ArrayList</classname> of non-Serializable <classname>org.springframework.http.MediaType</classname> instances.
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However you are able to inject your own implementation of the <classname>Serializer</classname> and/or
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<classname>Deserializer</classname> strategy interfaces into some <classname>MessageStore</classname> implementations
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(such as JdbcMessageStore) to change the behaviour of serialization and deserialization.
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</para>
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<para>
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Special attention must be paid to the headers that represent certain types of data.
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For example, if one of the headers contains an instance of some <emphasis>Spring Bean</emphasis>, upon deserialization you may end
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up with a different instance of that bean,
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which directly affects some of the implicit headers created by the framework (e.g., REPLY_CHANNEL or ERROR_CHANNEL).
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Currently they are not serializable, but even if they were the deserialized channel would not represent the expected instance.
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As a workaround we suggest to remove bean-ref headers via a <literal><header-filter/></literal>
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before sending a message to an endpoint backed by a persistent <classname>MessageStore</classname>.
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Also, we recommend using channel names instead of channel instances when setting those types of headers,
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thus allowing it to be resolved in real time by the <classname>ChannelResolver</classname>.
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</para>
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<para>
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Also avoid configuration of a message-flow like this:
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<emphasis>gateway -> queue-channel (backed by a persistent Message Store) -> service-activator</emphasis>
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That gateway creates a <emphasis>Temporary Reply Channel</emphasis> in the background, and it will be lost by the time the
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service-activator's poller reads from the queue, because it has been deserialized by another thread on the sending side.
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</para>
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<para>
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Nevertheless we are constantly thinking about potential improvements to the framework, such as a way to provide some
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robust default serialization strategy for messages in these cases.
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</para>
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</important>
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</para>
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</section>
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