Inbound Channel Adapters

通常，消息流从入站通道适配器开始（例如 <int-jdbc:inbound-channel-adapter>）。适配器使用 <poller> 配置，它要求一个 MessageSource<?> 定期生成消息。Java DSL 允许从 MessageSource<?> 启动 IntegrationFlow。为此，IntegrationFlow fluent API 提供了一个重载 IntegrationFlow.from(MessageSource<?> messageSource) 方法。你可以将 MessageSource<?> 配置为 bean，并将其作为该方法的参数提供。IntegrationFlow.from() 的第二个参数是 Consumer<SourcePollingChannelAdapterSpec> lambda，它允许你为 SourcePollingChannelAdapter 提供选项（例如 PollerMetadata 或 SmartLifecycle）。以下示例展示了如何使用 fluent API 和 lambda 来创建 IntegrationFlow：

Typically, message flows start from an inbound channel adapter (such as <int-jdbc:inbound-channel-adapter>). The adapter is configured with <poller>, and it asks a MessageSource<?> to periodically produce messages. Java DSL allows for starting IntegrationFlow from a MessageSource<?>, too. For this purpose, the IntegrationFlow fluent API provides an overloaded IntegrationFlow.from(MessageSource<?> messageSource) method. You can configure the MessageSource<?> as a bean and provide it as an argument for that method. The second parameter of IntegrationFlow.from() is a Consumer<SourcePollingChannelAdapterSpec> lambda that lets you provide options (such as PollerMetadata or SmartLifecycle) for the SourcePollingChannelAdapter. The following example shows how to use the fluent API and a lambda to create an IntegrationFlow:

@Bean
public MessageSource<Object> jdbcMessageSource() {
    return new JdbcPollingChannelAdapter(this.dataSource, "SELECT * FROM something");
}

@Bean
public IntegrationFlow pollingFlow() {
    return IntegrationFlow.from(jdbcMessageSource(),
                c -> c.poller(Pollers.fixedRate(100).maxMessagesPerPoll(1)))
            .transform(Transformers.toJson())
            .channel("furtherProcessChannel")
            .get();
}

对于那些不需要直接构建 Message 对象的情况，你可以使用基于 java.util.function.Supplier 的 IntegrationFlow.fromSupplier() 变体。Supplier.get() 的结果将自动包装进一个 Message（如果它还没有是一个 Message 的话）。

For those cases that have no requirements to build Message objects directly, you can use a IntegrationFlow.fromSupplier() variant that is based on the java.util.function.Supplier . The result of the Supplier.get() is automatically wrapped in a Message (if it is not already a Message).