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* Mostly driver by suggestions from IDEA language plugin * Add Maven-Gradle code switch for dependency in the modules
87 lines
4.2 KiB
Plaintext
87 lines
4.2 KiB
Plaintext
[[resource]]
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== Resource Support
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The resource inbound channel adapter builds upon Spring's `Resource` abstraction to support greater flexibility across a variety of actual types of underlying resources, such as a file, a URL, or a class path resource.
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Therefore, it is similar to but more generic than the file inbound channel adapter.
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[[resource-inbound-channel-adapter]]
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=== Resource Inbound Channel Adapter
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The resource inbound channel adapter is a polling adapter that creates a `Message` whose payload is a collection of `Resource` objects.
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`Resource` objects are resolved based on the pattern specified by the `pattern` attribute.
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The collection of resolved `Resource` objects is then sent as a payload within a `Message` to the adapter's channel.
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That is one major difference between resource inbound channel adapter and file inbound channel adapter: The latter buffers `File` objects and sends a single `File` object per `Message`.
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The following example shows a simple configuration that finds all files that end with the 'properties' extension in the `things.thing1` package available on the classpath and sends them as the payload of a `Message` to the channel named '`resultChannel`':
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====
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[source,xml]
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----
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<int:resource-inbound-channel-adapter id="resourceAdapter"
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channel="resultChannel"
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pattern="classpath:things/thing1/*.properties">
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<int:poller fixed-rate="1000"/>
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</int:resource-inbound-channel-adapter>
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----
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====
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The resource inbound channel adapter relies on the `org.springframework.core.io.support.ResourcePatternResolver` strategy interface to resolve the provided pattern.
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It defaults to an instance of the current `ApplicationContext`.
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However, you can provide a reference to an instance of your own implementation of `ResourcePatternResolver` by setting the `pattern-resolver` attribute, as the following example shows:
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====
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[source,xml]
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----
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<int:resource-inbound-channel-adapter id="resourceAdapter"
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channel="resultChannel"
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pattern="classpath:things/thing1/*.properties"
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pattern-resolver="myPatternResolver">
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<int:poller fixed-rate="1000"/>
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</int:resource-inbound-channel-adapter>
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<bean id="myPatternResolver" class="org.example.MyPatternResolver"/>
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----
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====
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You may have a use case where you need to further filter the collection of resources resolved by the `ResourcePatternResolver`.
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For example, you may want to prevent resources that were already resolved from appearing in a collection of resolved resources ever again.
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On the other hand, your resources might be updated rather often, and you _do_ want them to be picked up again.
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In other words, both defining an additional filter and disabling filtering altogether are valid use cases.
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You can provide your own implementation of the `org.springframework.integration.util.CollectionFilter` strategy interface, as the following example shows:
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====
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[source,java]
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----
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public interface CollectionFilter<T> {
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Collection<T> filter(Collection<T> unfilteredElements);
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}
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----
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====
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The `CollectionFilter` receives a collection of un-filtered elements (which are `Resource` objects in the preceding example), and it returns a collection of filtered elements of that same type.
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If you define the adapter with XML but you do not specify a filter reference, the resource inbound channel adapter uses a default implementation of `CollectionFilter`.
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The implementation class of that default filter is `org.springframework.integration.util.AcceptOnceCollectionFilter`.
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It remembers the elements passed in the previous invocation in order to avoid returning those elements more than once.
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To inject your own implementation of `CollectionFilter` instead, use the `filter` attribute, as the following example shows:
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====
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[source,xml]
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----
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<int:resource-inbound-channel-adapter id="resourceAdapter"
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channel="resultChannel"
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pattern="classpath:things/thing1/*.properties"
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filter="myFilter">
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<int:poller fixed-rate="1000"/>
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</int:resource-inbound-channel-adapter>
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<bean id="myFilter" class="org.example.MyFilter"/>
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----
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====
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If you do not need any filtering and want to disable even the default `CollectionFilter` strategy, provide an empty value for the filter attribute (for example, `filter=""`)
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