DSL: Polishing AMQP ICA Spec

Also add `messageHeaders()` to `MessageSourceSpec`.

Author: garyrussell

spring-integration-amqp/src/main/java/org/springframework/integration/amqp/dsl/AmqpInboundPolledChannelAdapterSpec.java

@@ -50,17 +50,17 @@ public AmqpInboundPolledChannelAdapterSpec transacted(boolean transacted) {
 		return this;
 	}
 
-	public AmqpInboundPolledChannelAdapterSpec setPropertiesConverter(MessagePropertiesConverter propertiesConverter) {
+	public AmqpInboundPolledChannelAdapterSpec propertiesConverter(MessagePropertiesConverter propertiesConverter) {
 		this.target.setPropertiesConverter(propertiesConverter);
 		return this;
 	}
 
-	public AmqpInboundPolledChannelAdapterSpec setHeaderMapper(AmqpHeaderMapper headerMapper) {
+	public AmqpInboundPolledChannelAdapterSpec headerMapper(AmqpHeaderMapper headerMapper) {
 		this.target.setHeaderMapper(headerMapper);
 		return this;
 	}
 
-	public AmqpInboundPolledChannelAdapterSpec setMessageConverter(MessageConverter messageConverter) {
+	public AmqpInboundPolledChannelAdapterSpec messageConverter(MessageConverter messageConverter) {
 		this.target.setMessageConverter(messageConverter);
 		return this;
 	}

spring-integration-core/src/main/java/org/springframework/integration/dsl/MessageSourceSpec.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 the original author or authors.
+ * Copyright 2016-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,12 @@
 
 package org.springframework.integration.dsl;
 
+import java.util.Map;
+
+import org.springframework.expression.Expression;
 import org.springframework.integration.core.MessageSource;
+import org.springframework.integration.endpoint.AbstractMessageSource;
+import org.springframework.util.Assert;
 
 /**
  * An {@link IntegrationComponentSpec} for {@link MessageSource}s.
@@ -25,9 +30,26 @@
  * @param <H> the target {@link MessageSource} implementation type.
  *
  * @author Artem Bilan
+ * @author Gary Russell
  *
  * @since 5.0
  */
 public abstract class MessageSourceSpec<S extends MessageSourceSpec<S, H>, H extends MessageSource<?>>
 		extends IntegrationComponentSpec<S, H> {
+
+	/**
+	 * Expressions with which to enhance headers.
+	 * Only applies to subclasses of {@link AbstractMessageSource}.
+	 * @param headerExpressions the header expressions.
+	 * @return the spec.
+	 * @since 5.0.1
+	 */
+	public S messageHeaders(Map<String, Expression> headerExpressions) {
+		Assert.state(this.target instanceof AbstractMessageSource,
+				() -> "'MessageSource' must be an instance of 'AbstractMessageSource', not "
+					+ this.target.getClass());
+		((AbstractMessageSource<?>) this.target).setHeaderExpressions(headerExpressions);
+		return _this();
+	}
+
 }