INT-2453 content-type and ObjectToJsonTransformer

Added 'content-type' functionality to ObjectToJsonTransformer

Added 'content-type' attribute to object-to-json-transformer element

Added parser and usage tests to ensure propper overrides
(see Mark's last comment here https://github.com/SpringSource/spring-integration/pull/409)

Applied required changes to Amqp module to work with standard 'content-type' header

INT-2453 polish based on PR comments

INT-2453 polished test

INT-2453 polished parser

spring-integration-core/src/main/java/org/springframework/integration/MessageHeaders.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -86,6 +86,8 @@ public final class MessageHeaders implements Map<String, Object>, Serializable {
 
 	public static final String SEQUENCE_DETAILS = "sequenceDetails";
 
+	public static final String CONTENT_TYPE = "content-type";
+
 
 	private final Map<String, Object> headers;
 

spring-integration-core/src/main/java/org/springframework/integration/config/xml/ObjectToJsonTransformerParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -18,11 +18,13 @@ package org.springframework.integration.config.xml;
 
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.xml.ParserContext;
+import org.springframework.integration.MessageHeaders;
 import org.springframework.util.StringUtils;
 import org.w3c.dom.Element;
 
 /**
  * @author Mark Fisher
+ * @author Oleg Zhurakousky
  * @since 2.0
  */
 public class ObjectToJsonTransformerParser extends AbstractTransformerParser {
@@ -38,6 +40,8 @@ public class ObjectToJsonTransformerParser extends AbstractTransformerParser {
 		if (StringUtils.hasText(objectMapper)) {
 			builder.addConstructorArgReference(objectMapper);
 		}
+		if (element.hasAttribute(MessageHeaders.CONTENT_TYPE)){
+			builder.addPropertyValue("contentType", element.getAttribute("content-type"));
+		}
 	}
-
-}
+}

spring-integration-core/src/main/java/org/springframework/integration/json/ObjectToJsonTransformer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -13,26 +13,35 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.integration.json;
 
 import java.io.StringWriter;
 
 import org.codehaus.jackson.map.ObjectMapper;
 
-import org.springframework.integration.transformer.AbstractPayloadTransformer;
+import org.springframework.integration.Message;
+import org.springframework.integration.MessageHeaders;
+import org.springframework.integration.support.MessageBuilder;
+import org.springframework.integration.transformer.AbstractTransformer;
 import org.springframework.util.Assert;
+import org.springframework.util.LinkedCaseInsensitiveMap;
 
 /**
  * Transformer implementation that converts a payload instance into a JSON string representation.
  *
  * @author Mark Fisher
+ * @author James Carr
+ * @author Oleg Zhurakousky
  * @since 2.0
  */
-public class ObjectToJsonTransformer extends AbstractPayloadTransformer<Object, String> {
+public class ObjectToJsonTransformer extends AbstractTransformer {
+
+	public static final String JSON_CONTENT_TYPE = "application/json";
 
 	private final ObjectMapper objectMapper;
 
+	private volatile String contentType = JSON_CONTENT_TYPE;
+	private volatile boolean contentTypeExplicitlySet = false;
 
 	public ObjectToJsonTransformer(ObjectMapper objectMapper) {
 		Assert.notNull(objectMapper, "objectMapper must not be null");
@@ -43,11 +52,42 @@ public class ObjectToJsonTransformer extends AbstractPayloadTransformer<Object,
 		this.objectMapper = new ObjectMapper();
 	}
 
+	/**
+	 * Sets the content-type header value
+	 *
+	 * @param contentType
+	 */
+	public void setContentType(String contentType){
+		// only null assertion is needed since "" is a valid value
+		Assert.notNull(contentType, "'contentType' must not be null");
+		this.contentTypeExplicitlySet = true;
+		this.contentType = contentType;
+	}
 
-	protected String transformPayload(Object payload) throws Exception {
+	private String transformPayload(Object payload) throws Exception {
 		StringWriter writer = new StringWriter();
 		this.objectMapper.writeValue(writer, payload);
 		return writer.toString();
 	}
 
-}
+	@Override
+	protected Object doTransform(Message<?> message) throws Exception {
+		String payload = this.transformPayload(message.getPayload());
+		MessageBuilder<String> messageBuilder = MessageBuilder.withPayload(payload);
+
+		LinkedCaseInsensitiveMap<Object> headers = new LinkedCaseInsensitiveMap<Object>();
+		headers.putAll(message.getHeaders());
+
+		if (headers.containsKey(MessageHeaders.CONTENT_TYPE)) {
+			if (this.contentTypeExplicitlySet){
+				// override
+				headers.put(MessageHeaders.CONTENT_TYPE, this.contentType);
+			}
+		}
+		else {
+			headers.put(MessageHeaders.CONTENT_TYPE, this.contentType);
+		}
+		messageBuilder.copyHeaders(headers);
+		return messageBuilder.build();
+	}
+}

spring-integration-core/src/main/java/org/springframework/integration/mapping/AbstractHeaderMapper.java

@@ -268,7 +268,7 @@ public abstract class AbstractHeaderMapper<T> implements RequestReplyHeaderMappe
 	 */
 	private String addPrefixIfNecessary(String prefix, String propertyName) {
 		String headerName = propertyName;
-		if (StringUtils.hasText(prefix) && !headerName.startsWith(prefix)) {
+		if (StringUtils.hasText(prefix) && !headerName.startsWith(prefix) && !headerName.equals(MessageHeaders.CONTENT_TYPE)) {
 			headerName = prefix + propertyName;
 		}
 		return headerName;

spring-integration-core/src/main/resources/org/springframework/integration/config/xml/spring-integration-2.2.xsd

@@ -2017,6 +2017,15 @@
 		<xsd:choice minOccurs="0" maxOccurs="unbounded">
 			<xsd:element ref="poller" />
 		</xsd:choice>
+		<xsd:attribute name="content-type" use="optional">
+			<xsd:annotation>
+				<xsd:documentation>
+					Allows you to set 'content-type' Message header. In the case that a content-type header is already present,
+					we will only override that value IF this attribute is explicitely set with
+					content-type value (e.g., content-type="text/xml")
+				</xsd:documentation>
+			</xsd:annotation>
+		</xsd:attribute>
 		<xsd:attribute name="object-mapper" use="optional">
 			<xsd:annotation>
 				<xsd:documentation>