Set message header using BindingProperties' contentType

- Update MessageConverterConfigurer that uses a channel interceptor to check if the message contentType header is missing and if there is a binding property for `contentType` header is provided, then set that value as the message contentType header

This resolves #397

Add test

spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/config/ContentTypeConfigurerTests.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2015 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.cloud.stream.config;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.junit.Assert.assertThat;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.SpringApplicationConfiguration;
+import org.springframework.cloud.stream.annotation.Bindings;
+import org.springframework.cloud.stream.annotation.EnableBinding;
+import org.springframework.cloud.stream.binder.BinderFactory;
+import org.springframework.cloud.stream.messaging.Source;
+import org.springframework.cloud.stream.test.binder.TestSupportBinder;
+import org.springframework.context.annotation.PropertySource;
+import org.springframework.integration.support.MessageBuilder;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+/**
+ * @author Ilayaperumal Gopinathan
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringApplicationConfiguration({ContentTypeConfigurerTests.TestSource.class})
+public class ContentTypeConfigurerTests {
+
+	@Autowired @Bindings(TestSource.class)
+	private Source testSource;
+
+	@Autowired
+	private BinderFactory binderFactory;
+
+	@Test
+	public void testMessageHeaderWhenNoExplicitContentType() throws Exception {
+		testSource.output().send(MessageBuilder.withPayload("{\"message\":\"Hi\"}").build());
+		Message<String> received = (Message<String>) ((TestSupportBinder) binderFactory.getBinder(null)).messageCollector().forChannel(testSource.output()).poll();
+		assertThat(received.getHeaders().get(MessageHeaders.CONTENT_TYPE).toString(), equalTo("application/json"));
+		assertThat(received.getPayload(), equalTo("{\"message\":\"Hi\"}"));
+	}
+
+	@EnableBinding(Source.class)
+	@EnableAutoConfiguration
+	@PropertySource("classpath:/org/springframework/cloud/stream/config/channel/source-channel-configurers.properties")
+	public static class TestSource {
+
+	}
+}
+

spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/config/MessageChannelConfigurerTests.java

@@ -52,7 +52,7 @@ public class MessageChannelConfigurerTests {
 	private Sink testSink;
 
 	@Test
-	public void testContentTypeConfigurer() throws Exception {
+	public void testMessageConverterConfigurer() throws Exception {
 		final CountDownLatch latch = new CountDownLatch(1);
 		MessageHandler messageHandler = new MessageHandler() {
 			@Override

spring-cloud-stream-integration-tests/src/test/resources/org/springframework/cloud/stream/config/channel/source-channel-configurers.properties

@@ -0,0 +1,2 @@
+spring.cloud.stream.bindings.output.destination=interceptor-test
+spring.cloud.stream.bindings.output.contentType=application/json