`MessageChannelSpec.wireTap()`

Spring Integration includes a .wireTap() fluent API MessageChannelSpec builders. The following example shows how to use the wireTap method to log input:

@Bean
public QueueChannelSpec myChannel() {
    return MessageChannels.queue()
            .wireTap("loggingFlow.input");
}

@Bean
public IntegrationFlow loggingFlow() {
    return f -> f.log();
}

If the MessageChannel is an instance of InterceptableChannel, the log(), wireTap() or intercept() operators are applied to the current MessageChannel. Otherwise, an intermediate DirectChannel is injected into the flow for the currently configured endpoint. In the following example, the WireTap interceptor is added to myChannel directly, because DirectChannel implements InterceptableChannel:

@Bean
MessageChannel myChannel() {
    return new DirectChannel();
}

...
    .channel(myChannel())
    .log()
}

When the current MessageChannel does not implement InterceptableChannel, an implicit DirectChannel and BridgeHandler are injected into the IntegrationFlow, and the WireTap is added to this new DirectChannel. The following example does not have any channel declaration:

.handle(...)
.log()
}

In the preceding example (and any time no channel has been declared), an implicit DirectChannel is injected in the current position of the IntegrationFlow and used as an output channel for the currently configured ServiceActivatingHandler (from the .handle(), described earlier).