Add nullChannel DSL element to Groovy DSL

spring-integration-groovy/src/main/groovy/org/springframework/integration/groovy/dsl/GroovyIntegrationFlowDefinition.groovy

@@ -103,6 +103,17 @@ class GroovyIntegrationFlowDefinition {
 		this
 	}
 
+	/**
+	 * Populate a {@link org.springframework.integration.channel.NullChannel} instance
+	 * at the current {@link IntegrationFlow} chain position.
+	 * The nullChannel acts like "/dev/null".
+	 * @see org.springframework.integration.channel.NullChannel
+	 */
+	GroovyIntegrationFlowDefinition nullChannel() {
+		this.delegate.nullChannel()
+		this
+	}
+
 	/**
 	 * Populate a {@link org.springframework.integration.dsl.support.MessageChannelReference} instance
 	 * at the current {@link IntegrationFlow} chain position.

spring-integration-groovy/src/test/groovy/org/springframework/integration/groovy/dsl/test/GroovyDslTests.groovy

@@ -220,6 +220,50 @@ class GroovyDslTests {
 		assert groovyTestService.result.get() == 'TEST'
 	}
 
+	@Autowired
+	@Qualifier('nullChannelFlow.input')
+	private MessageChannel nullChannelFlowInput
+
+	@Test
+	void 'nullChannelFlow discards messages'() {
+		def wireTapChannel = new QueueChannel()
+		def testFlow = integrationFlow {
+			wireTap(wireTapChannel)
+			nullChannel()
+		}
+		def registration = this.integrationFlowContext.registration(testFlow).register()
+		registration.inputChannel.send(new GenericMessage<Object>('test'))
+		def tappedMessage = wireTapChannel.receive(1000)
+		registration.destroy()
+
+		assert tappedMessage?.payload == 'test' //verify that a message was sent and assume nullChannel discarded it.
+
+	}
+
+	@Autowired
+	@Qualifier('nullChannelWithTransformFlow.input')
+	private MessageChannel nullChannelWithTransformFlowInput
+
+	@Test
+	void 'nullChannel can be used after transform in a flow'() {
+		def wireTapChannel = new QueueChannel()
+		def testFlow = integrationFlow {
+			transform {
+				transformer { it.toUpperCase() }
+			}
+			wireTap(wireTapChannel)
+			nullChannel()
+		}
+		def registration = this.integrationFlowContext.registration(testFlow).register()
+		registration.inputChannel.send(new GenericMessage<Object>('test'))
+		def tappedMessage = wireTapChannel.receive(1000)
+		registration.destroy()
+
+		//verify that a message was sent, transformed and assume nullChannel discarded it.
+		assert tappedMessage?.payload == 'TEST'
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@EnableIntegration
 	static class Config {
@@ -361,6 +405,27 @@ class GroovyDslTests {
 
 		}
 
+		@Bean
+		nullChannelFlow() {
+			integrationFlow {
+				{
+					log LoggingHandler.Level.WARN, 'test.category'
+				}
+				nullChannel()
+			}
+
+		}
+
+		@Bean
+		nullChannelWithTransformFlow() {
+			integrationFlow {
+				transform {
+					transformer { it.toUpperCase() }
+				}
+				nullChannel()
+			}
+		}
+
 	}
 
 	@CompileStatic