Sub-flows support
一些 if…else 和 publish-subscribe 组件提供了使用子流程指定其逻辑或映射的功能。最简单的示例是 .publishSubscribeChannel(), 如下例所示：
Some of if…else and publish-subscribe components provide the ability to specify their logic or mapping by using sub-flows.
The simplest sample is .publishSubscribeChannel(), as the following example shows:
@Bean
public IntegrationFlow subscribersFlow() {
return flow -> flow
.publishSubscribeChannel(Executors.newCachedThreadPool(), s -> s
.subscribe(f -> f
.<Integer>handle((p, h) -> p / 2)
.channel(c -> c.queue("subscriber1Results")))
.subscribe(f -> f
.<Integer>handle((p, h) -> p * 2)
.channel(c -> c.queue("subscriber2Results"))))
.<Integer>handle((p, h) -> p * 3)
.channel(c -> c.queue("subscriber3Results"));
}可以使用单独的 IntegrationFlow @Bean 定义实现相同的结果，但我们希望你发现这种子流程逻辑组合样式很有用。我们发现它会导致代码更短（因此更具可读性）。
You can achieve the same result with separate IntegrationFlow @Bean definitions, but we hope you find the sub-flow style of logic composition useful.
We find that it results in shorter (and so more readable) code.
从 5.3 版本开始，提供了基于 BroadcastCapableChannel 的 publishSubscribeChannel() 实现，以在代理支持的消息通道上配置子流程订阅者。例如，我们现在可以将多个订阅者配置为 Jms.publishSubscribeChannel() 上的子流程：
Starting with version 5.3, a BroadcastCapableChannel-based publishSubscribeChannel() implementation is provided to configure sub-flow subscribers on broker-backed message channels.
For example, we now can configure several subscribers as sub-flows on the Jms.publishSubscribeChannel():
@Bean
public JmsPublishSubscribeMessageChannelSpec jmsPublishSubscribeChannel() {
return Jms.publishSubscribeChannel(jmsConnectionFactory())
.destination("pubsub");
}
@Bean
public IntegrationFlow pubSubFlow(BroadcastCapableChannel jmsPublishSubscribeChannel) {
return f -> f
.publishSubscribeChannel(jmsPublishSubscribeChannel,
pubsub -> pubsub
.subscribe(subFlow -> subFlow
.channel(c -> c.queue("jmsPubSubBridgeChannel1")))
.subscribe(subFlow -> subFlow
.channel(c -> c.queue("jmsPubSubBridgeChannel2"))));
}类似的 publish-subscribe 子流程组合提供了 .routeToRecipients() 方法。
A similar publish-subscribe sub-flow composition provides the .routeToRecipients() method.
另一个示例是在 .filter() 方法中使用 .discardFlow() 而不是 .discardChannel()。
Another example is using .discardFlow() instead of .discardChannel() on the .filter() method.
.route() 值得特别关注。考虑以下示例：
The .route() deserves special attention.
Consider the following example:
@Bean
public IntegrationFlow routeFlow() {
return f -> f
.<Integer, Boolean>route(p -> p % 2 == 0,
m -> m.channelMapping("true", "evenChannel")
.subFlowMapping("false", sf ->
sf.<Integer>handle((p, h) -> p * 3)))
.transform(Object::toString)
.channel(c -> c.queue("oddChannel"));
}.channelMapping() 继续像在常规 Router 映射中一样工作，但 .subFlowMapping() 将该子流程绑定到主流程。换言之，任何路由器的子流程都将在 .route() 之后返回到主流程。
The .channelMapping() continues to work as it does in regular Router mapping, but the .subFlowMapping() tied that sub-flow to the main flow.
In other words, any router’s sub-flow returns to the main flow after .route().
有时，你需要从 .subFlowMapping() 引用现有的 IntegrationFlow @Bean。以下示例演示了如何执行此操作：
Sometimes, you need to refer to an existing IntegrationFlow @Bean from the .subFlowMapping().
The following example shows how to do so:
@Bean
public IntegrationFlow splitRouteAggregate() {
return f -> f
.split()
.<Integer, Boolean>route(o -> o % 2 == 0,
m -> m
.subFlowMapping(true, oddFlow())
.subFlowMapping(false, sf -> sf.gateway(evenFlow())))
.aggregate();
}
@Bean
public IntegrationFlow oddFlow() {
return f -> f.handle(m -> System.out.println("odd"));
}
@Bean
public IntegrationFlow evenFlow() {
return f -> f.handle((p, h) -> "even");
}在这种情况下，当你需要从该子流程接收回复并继续主流程时，此 IntegrationFlow Bean 引用（或其输入通道）必须用 .gateway() 包装，如前一个示例所示。前一个示例中的 oddFlow() 引用没有包装到 .gateway()。因此，我们不希望从此路由分支获得回复。否则，你最终会遇到类似于以下内容的异常：
In this case, when you need to receive a reply from such a sub-flow and continue the main flow, this IntegrationFlow bean reference (or its input channel) has to be wrapped with a .gateway() as shown in the preceding example.
The oddFlow() reference in the preceding example is not wrapped to the .gateway().
Therefore, we do not expect a reply from this routing branch.
Otherwise, you end up with an exception similar to the following:
Caused by: org.springframework.beans.factory.BeanCreationException:
The 'currentComponent' (org.springframework.integration.router.MethodInvokingRouter@7965a51c)
is a one-way 'MessageHandler' and it isn’t appropriate to configure 'outputChannel'.
This is the end of the integration flow.
当你将子流程配置为 lambda 时，框架将处理与子流程的请求-回复交互，并且不需要网关。
When you configure a sub-flow as a lambda, the framework handles the request-reply interaction with the sub-flow and a gateway is not needed.
子流程可以嵌套到任何深度，但我们不建议这样做。事实上，即使在路由器的情况下，在流程中添加复杂的子流程也会很快看起来像一盘意大利面，并且对于人类来说很难解析。
Sub-flows can be nested to any depth, but we do not recommend doing so. In fact, even in the router case, adding complex sub-flows within a flow would quickly begin to look like a plate of spaghetti and be difficult for a human to parse.
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在 DSL 支持子流程配置的情况下，当组件配置通常需要通道并且该子流程以 In cases where the DSL supports a subflow configuration, when a channel is normally needed for the component being configured, and that subflow starts with a 框架在内部创建一个 the Framework internally creates a |