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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.
84 lines
5.4 KiB
XML
84 lines
5.4 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="feed"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Feed Adapter</title>
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<para>
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Spring Integration provides support for Syndication via Feed Adapters
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</para>
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<section id="feed-intro">
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<title>Introduction</title>
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<para>
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Web syndication is a form of publishing material such as news stories, press releases, blog posts, and
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other items typically available on a website but also made available in a feed format such as RSS or ATOM.
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</para>
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<para>
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Spring integration provides support for Web Syndication via its 'feed' adapter and provides convenient
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namespace-based configuration for it.
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To configure the 'feed' namespace, include the following elements within the headers of your XML configuration file:
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<programlisting language="xml"><![CDATA[xmlns:int-feed="http://www.springframework.org/schema/integration/feed"
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xsi:schemaLocation="http://www.springframework.org/schema/integration/feed
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http://www.springframework.org/schema/integration/feed/spring-integration-feed.xsd"]]></programlisting>
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</para>
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</section>
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<section>
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<title>Feed Inbound Channel Adapter</title>
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<para>
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The only adapter that is really needed to provide support for retrieving feeds is an <emphasis>inbound channel adapter</emphasis>.
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This allows you to subscribe to a particular URL. Below is an example configuration:
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<programlisting language="xml"><![CDATA[<int-feed:inbound-channel-adapter id="feedAdapter"
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channel="feedChannel"
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url="http://feeds.bbci.co.uk/news/rss.xml">
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<int:poller fixed-rate="10000" max-messages-per-poll="100" />
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</int-feed:inbound-channel-adapter>]]></programlisting>
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In the above configuration, we are subscribing to a URL identified by the <code>url</code> attribute.
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</para>
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<para>
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As news items are retrieved they will be converted to Messages and sent to a channel identified by the <code>channel</code> attribute.
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The payload of each message will be a <classname>com.sun.syndication.feed.synd.SyndEntry</classname> instance. That encapsulates
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various data about a news item (content, dates, authors, etc.).
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</para>
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<para>
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You can also see that the <emphasis>Inbound Feed Channel Adapter</emphasis> is a Polling Consumer. That means you have to
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provide a poller configuration. However, one important thing you must understand with regard to Feeds is that its inner-workings
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are slightly different then most other poling consumers. When an Inbound Feed adapter is started, it does the first poll and
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receives a <classname>com.sun.syndication.feed.synd.SyndEntryFeed</classname> instance. That is an object that contains multiple
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<classname>SyndEntry</classname> objects. Each entry is stored in the local entry queue and is released based on
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the value in the <code>max-messages-per-poll</code> attribute such that each Message will contain a single entry.
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If during retrieval of the entries from the entry queue the queue had become empty, the adapter will attempt to update
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the Feed thereby populating the queue with more entries (SyndEntry instances) if available. Otherwise the next attempt to
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poll for a feed will be determined by the trigger of the poller (e.g., every 10 seconds in the above configuration).
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</para>
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<para>
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<emphasis>Duplicate Entries</emphasis>
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</para>
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<para>
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Polling for a Feed might result in entries that have already been processed
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("I already read that news item, why are you showing it to me again?").
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Spring Integration provides a convenient mechanism to eliminate the need to worry about duplicate entries.
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Each feed entry will have a <emphasis>published date</emphasis> field. Every time a new Message is generated and sent,
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Spring Integration will store the value of the latest <emphasis>published date</emphasis> in an instance of the
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<classname>org.springframework.integration.store.MetadataStore</classname> strategy. The MetadataStore interface is
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designed to store various types of generic meta-data (e.g., published date of the last feed entry that has been processed)
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to help components such as this Feed adapter deal with duplicates.
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</para>
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<para>
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The default rule for locating this metadata store is as follows: Spring Integration will look for a bean of type
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<classname>org.springframework.integration.store.MetadataStore</classname> in the ApplicationContext. If one is found then it will be used,
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otherwise it will create a new instance of <classname>SimpleMetadataStore</classname> which is an in-memory implementation that
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will only persist metadata within the lifecycle of the currently running Application Context. This means that upon restart you may
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end up with duplicate entries. If you need to persist metadata between Application Context restarts, you may use the
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<classname>PropertiesPersistingMetadataStore</classname> which is backed by a properties file and a properties-persister.
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Alternatively, you could provide your own implementation of the <classname>MetadataStore</classname> interface
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(e.g. JdbcMetadataStore) and configure it as bean in the Application Context.
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<programlisting language="xml"><![CDATA[<bean id="metadataStore"
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class="org.springframework.integration.store.PropertiesPersistingMetadataStore"/>]]></programlisting>
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</para>
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</section>
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</chapter>
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