Support better HttpMessageConverters manipulation

Add additional constructor and a protected postProcessConverters method
to make it easier to manipulate the final converter list that will
be used.

Fixes gh-1482

Author: philwebb

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/HttpMessageConverters.java

@@ -69,26 +69,54 @@ public HttpMessageConverters(HttpMessageConverter<?>... additionalConverters) {
 	 * converters.
 	 * @param additionalConverters additional converters to be added. Items are added just
 	 * before any default converter of the same type (or at the front of the list if no
-	 * default converter is found) The {@link #getConverters()} methods can be used for
-	 * further converter manipulation.
+	 * default converter is found) The {@link #postProcessConverters(List)} method can be
+	 * used for further converter manipulation.
 	 */
 	public HttpMessageConverters(Collection<HttpMessageConverter<?>> additionalConverters) {
-		List<HttpMessageConverter<?>> converters = new ArrayList<HttpMessageConverter<?>>();
+		this(true, additionalConverters);
+	}
+
+	/**
+	 * Create a new {@link HttpMessageConverters} instance with the specified converters.
+	 * @param addDefaultConverters if default converters should be added
+	 * @param converters converters to be added. Items are added just before any default
+	 * converter of the same type (or at the front of the list if no default converter is
+	 * found) The {@link #postProcessConverters(List)} method can be used for further
+	 * converter manipulation.
+	 */
+	public HttpMessageConverters(boolean addDefaultConverters,
+			Collection<HttpMessageConverter<?>> converters) {
+		List<HttpMessageConverter<?>> combined = new ArrayList<HttpMessageConverter<?>>();
 		List<HttpMessageConverter<?>> processing = new ArrayList<HttpMessageConverter<?>>(
-				additionalConverters);
-		for (HttpMessageConverter<?> defaultConverter : getDefaultConverters()) {
-			Iterator<HttpMessageConverter<?>> iterator = processing.iterator();
-			while (iterator.hasNext()) {
-				HttpMessageConverter<?> candidate = iterator.next();
-				if (ClassUtils.isAssignableValue(defaultConverter.getClass(), candidate)) {
-					converters.add(candidate);
-					iterator.remove();
+				converters);
+		if (addDefaultConverters) {
+			for (HttpMessageConverter<?> defaultConverter : getDefaultConverters()) {
+				Iterator<HttpMessageConverter<?>> iterator = processing.iterator();
+				while (iterator.hasNext()) {
+					HttpMessageConverter<?> candidate = iterator.next();
+					if (ClassUtils.isAssignableValue(defaultConverter.getClass(),
+							candidate)) {
+						combined.add(candidate);
+						iterator.remove();
+					}
 				}
+				combined.add(defaultConverter);
 			}
-			converters.add(defaultConverter);
 		}
-		converters.addAll(0, processing);
-		this.converters = Collections.unmodifiableList(converters);
+		combined.addAll(0, processing);
+		combined = postProcessConverters(combined);
+		this.converters = Collections.unmodifiableList(combined);
+	}
+
+	/**
+	 * Method that can be used to post-process the {@link HttpMessageConverter} list
+	 * before it is used.
+	 * @param converters a mutable list of the converters that will be used.
+	 * @return the final converts list to use
+	 */
+	protected List<HttpMessageConverter<?>> postProcessConverters(
+			List<HttpMessageConverter<?>> converters) {
+		return converters;
 	}
 
 	private List<HttpMessageConverter<?>> getDefaultConverters() {
@@ -127,8 +155,8 @@ public Iterator<HttpMessageConverter<?>> iterator() {
 	}
 
 	/**
-	 * Return a mutable list of the converters in the order that they will be registered.
-	 * Values in the list cannot be modified once the bean has been initialized.
+	 * Return an immutable list of the converters in the order that they will be
+	 * registered.
 	 * @return the converters
 	 */
 	public List<HttpMessageConverter<?>> getConverters() {

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/HttpMessageConvertersTests.java

@@ -18,6 +18,7 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Iterator;
 import java.util.List;
 
 import org.junit.Rule;
@@ -97,4 +98,30 @@ public void addNewConverters() {
 		assertEquals(converter2, converters.getConverters().get(1));
 	}
 
+	@Test
+	public void postProcessConverters() throws Exception {
+		HttpMessageConverters converters = new HttpMessageConverters() {
+			@Override
+			protected List<HttpMessageConverter<?>> postProcessConverters(
+					List<HttpMessageConverter<?>> converters) {
+				for (Iterator<HttpMessageConverter<?>> iterator = converters.iterator(); iterator
+						.hasNext();) {
+					if (iterator.next() instanceof Jaxb2RootElementHttpMessageConverter) {
+						iterator.remove();
+					}
+				}
+				return converters;
+			};
+		};
+		List<Class<?>> converterClasses = new ArrayList<Class<?>>();
+		for (HttpMessageConverter<?> converter : converters) {
+			converterClasses.add(converter.getClass());
+		}
+		assertThat(converterClasses, equalTo(Arrays.<Class<?>> asList(
+				ByteArrayHttpMessageConverter.class, StringHttpMessageConverter.class,
+				ResourceHttpMessageConverter.class, SourceHttpMessageConverter.class,
+				AllEncompassingFormHttpMessageConverter.class,
+				MappingJackson2HttpMessageConverter.class)));
+	}
+
 }