SPR-6932 Add option to extract value from single-key models in MappingJacksonJsonView

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/view/json/MappingJacksonJsonView.java

@@ -43,6 +43,7 @@ import org.springframework.web.servlet.view.AbstractView;
  *
  * @author Jeremy Grelle
  * @author Arjen Poutsma
+ * @author Rossen Stoyanchev
  * @see org.springframework.http.converter.json.MappingJacksonHttpMessageConverter
  * @since 3.0
  */
@@ -61,8 +62,10 @@ public class MappingJacksonJsonView extends AbstractView {
 
 	private Set<String> renderedAttributes;
 
-	private boolean disableCaching = true;
+	private boolean extractValueFromSingleKeyModel = false;
 
+	private boolean disableCaching = true;
+	
 	/**
 	 * Construct a new {@code JacksonJsonView}, setting the content type to {@code application/json}.
 	 */
@@ -127,6 +130,19 @@ public class MappingJacksonJsonView extends AbstractView {
 		this.disableCaching = disableCaching;
 	}
 
+	/**
+	 * Set whether to serialize models containing a single attribute as a map or whether to 
+	 * extract the single value from the model and serialize it directly.
+	 * The effect of setting this flag is similar to using 
+	 * {@code MappingJacksonHttpMessageConverter} with an {@code @ResponseBody}.
+	 * request-handling method.  
+	 * 
+	 * <p>Default is {@code false}. 
+	 */
+	public void setExtractValueFromSingleKeyModel(boolean extractValueFromSingleKeyModel) {
+		this.extractValueFromSingleKeyModel = extractValueFromSingleKeyModel;
+	}
+
 	@Override
 	protected void prepareResponse(HttpServletRequest request, HttpServletResponse response) {
 		response.setContentType(getContentType());
@@ -170,7 +186,7 @@ public class MappingJacksonJsonView extends AbstractView {
 				result.put(entry.getKey(), entry.getValue());
 			}
 		}
-		return result;
+		return (this.extractValueFromSingleKeyModel && result.size() == 1) ? result.values().iterator().next() : result;
 	}
 
 }

org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/view/json/MappingJacksonJsonViewTest.java

@@ -194,6 +194,36 @@ public class MappingJacksonJsonViewTest {
 		validateResult();
 	}
 
+	@Test
+	public void filterSingleKeyModel() throws Exception {
+		view.setExtractValueFromSingleKeyModel(true);
+
+		Map<String, Object> model = new HashMap<String, Object>();
+		TestBeanSimple bean = new TestBeanSimple();
+		model.put("foo", bean);
+
+		Object actual = view.filterModel(model);
+		
+		assertSame(bean, actual);
+	}
+	
+	@Test
+	public void filterTwoKeyModel() throws Exception {
+		view.setExtractValueFromSingleKeyModel(true);
+
+		Map<String, Object> model = new HashMap<String, Object>();
+		TestBeanSimple bean1 = new TestBeanSimple();
+		TestBeanSimple bean2 = new TestBeanSimple();
+		model.put("foo1", bean1);
+		model.put("foo2", bean2);
+
+		Object actual = view.filterModel(model);
+
+		assertTrue(actual instanceof Map);
+		assertSame(bean1, ((Map) actual).get("foo1"));
+		assertSame(bean2, ((Map) actual).get("foo2"));
+	}
+
 	private void validateResult() throws Exception {
 		Object jsResult =
 				jsContext.evaluateString(jsScope, "(" + response.getContentAsString() + ")", "JSON Stream", 1, null);

spring-framework-reference/src/view.xml

@@ -2610,7 +2610,9 @@ simpleReport.reportDataKey=myBeanData</programlisting>
   	of framework-specific classes) will be encoded as JSON. For cases where the 
   	contents of the map need to be filtered, users may specify a specific set of 
   	model attributes to encode via the <literal>RenderedAttributes</literal> 
-  	property.</para>
+  	property. The <literal>extractValueFromSingleKeyModel</literal> property
+  	may also be  used to have the value in single-key models extracted and 
+  	serialized directly rather than as a map of model attributes.</para>
 
 	<para>JSON mapping can be customized as needed through the use of Jackson's provided 
 	annotations. When further control is needed, a custom