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128 lines
4.3 KiB
Plaintext
128 lines
4.3 KiB
Plaintext
[[bridge]]
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=== Messaging Bridge
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A messaging bridge is a relatively trivial endpoint that connects two message channels or channel adapters.
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For example, you may want to connect a `PollableChannel` to a `SubscribableChannel` so that the subscribing endpoints do not have to worry about any polling configuration.
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Instead, the messaging bridge provides the polling configuration.
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By providing an intermediary poller between two channels, you can use a messaging bridge to throttle inbound messages.
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The poller's trigger determines the rate at which messages arrive on the second channel, and the poller's `maxMessagesPerPoll` property enforces a limit on the throughput.
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Another valid use for a messaging bridge is to connect two different systems.
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In such a scenario, Spring Integration's role is limited to making the connection between these systems and managing a poller, if necessary.
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It is probably more common to have at least a transformer between the two systems, to translate between their formats.
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In that case, the channels can be provided as the 'input-channel' and 'output-channel' of a transformer endpoint.
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If data format translation is not required, the messaging bridge may indeed be sufficient.
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[[bridge-namespace]]
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==== Configuring a Bridge with XML
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You can use the `<bridge>` element is used to create a messaging bridge between two message channels or channel adapters.
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To do so, provide the `input-channel` and `output-channel` attributes, as the following example shows:
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====
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[source,xml]
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----
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<int:bridge input-channel="input" output-channel="output"/>
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----
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====
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As mentioned above, a common use case for the messaging bridge is to connect a `PollableChannel` to a `SubscribableChannel`.
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When performing this role, the messaging bridge may also serve as a throttler:
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====
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[source,xml]
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----
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<int:bridge input-channel="pollable" output-channel="subscribable">
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<int:poller max-messages-per-poll="10" fixed-rate="5000"/>
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</int:bridge>
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----
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====
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You can use a similar mechanism to connecting channel adapters.
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The following example shows a simple "`echo`" between the `stdin` and `stdout` adapters from Spring Integration's `stream` namespace:
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====
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[source,xml]
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----
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<int-stream:stdin-channel-adapter id="stdin"/>
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<int-stream:stdout-channel-adapter id="stdout"/>
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<int:bridge id="echo" input-channel="stdin" output-channel="stdout"/>
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----
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====
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Similar configurations work for other (potentially more useful) Channel Adapter bridges, such as file-to-JMS or mail-to-file.
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Upcoming chapters cover the various channel adapters.
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NOTE: If no 'output-channel' is defined on a bridge, the reply channel provided by the inbound message is used, if available.
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If neither an output nor a reply channel is available, an exception is thrown.
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[[bridge-annot]]
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==== Configuring a Bridge with Java Configuration
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The following example shows how to configure a bridge in Java by using the `@BridgeFrom` annotation:
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====
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[source, java]
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----
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@Bean
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public PollableChannel polled() {
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return new QueueChannel();
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}
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@Bean
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@BridgeFrom(value = "polled", poller = @Poller(fixedDelay = "5000", maxMessagesPerPoll = "10"))
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public SubscribableChannel direct() {
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return new DirectChannel();
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}
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----
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====
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The following example shows how to configure a bridge in Java by using the `@BridgeTo` annotation:
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[source, java]
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----
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@Bean
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@BridgeTo(value = "direct", poller = @Poller(fixedDelay = "5000", maxMessagesPerPoll = "10"))
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public PollableChannel polled() {
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return new QueueChannel();
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}
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@Bean
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public SubscribableChannel direct() {
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return new DirectChannel();
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}
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----
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Alternately, you can use a `BridgeHandler`, as the following example shows:
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[source, java]
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----
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@Bean
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@ServiceActivator(inputChannel = "polled",
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poller = @Poller(fixedRate = "5000", maxMessagesPerPoll = "10"))
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public BridgeHandler bridge() {
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BridgeHandler bridge = new BridgeHandler();
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bridge.setOutputChannelName("direct");
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return bridge;
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}
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----
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[[bridge-dsl]]
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==== Configuring a Bridge with the Java DSL
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You can use the Java Domain Specific Language (DSL) to configure a bridge, as the following example shows:
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[source, java]
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----
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@Bean
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public IntegrationFlow bridgeFlow() {
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return IntegrationFlows.from("polled")
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.bridge(e -> e.poller(Pollers.fixedDelay(5000).maxMessagesPerPoll(10)))
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.channel("direct")
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.get();
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}
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----
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