Add support for sorting json keys

Add `jsonSortKeys` property to HttpMapperProperties.

Fixes gh-498

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

@@ -21,11 +21,16 @@ import org.springframework.http.converter.HttpMessageConverter;
 
 /**
  * Configuration properties to configure {@link HttpMessageConverter}s.
+ * 
+ * @author Dave Syer
+ * @author Piotr Maj
  */
 @ConfigurationProperties(name = "http.mappers", ignoreUnknownFields = false)
 public class HttpMapperProperties {
 
-	private boolean jsonPrettyPrint = false;
+	private boolean jsonPrettyPrint;
+
+	private boolean jsonSortKeys;
 
 	public void setJsonPrettyPrint(boolean jsonPrettyPrint) {
 		this.jsonPrettyPrint = jsonPrettyPrint;
@@ -35,4 +40,12 @@ public class HttpMapperProperties {
 		return this.jsonPrettyPrint;
 	}
 
+	public void setJsonSortKeys(boolean jsonSortKeys) {
+		this.jsonSortKeys = jsonSortKeys;
+	}
+
+	public boolean isJsonSortKeys() {
+		return this.jsonSortKeys;
+	}
+
 }

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

@@ -38,12 +38,14 @@ import org.springframework.http.converter.json.MappingJackson2HttpMessageConvert
 
 import com.fasterxml.jackson.databind.Module;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for {@link HttpMessageConverter}s.
  * 
  * @author Dave Syer
  * @author Christian Dupuis
+ * @author Piotr Maj
  */
 @Configuration
 @ConditionalOnClass(HttpMessageConverter.class)
@@ -87,7 +89,12 @@ public class HttpMessageConvertersAutoConfiguration {
 		@ConditionalOnMissingBean
 		@Primary
 		public ObjectMapper jacksonObjectMapper() {
-			return new ObjectMapper();
+			ObjectMapper objectMapper = new ObjectMapper();
+			if (this.properties.isJsonSortKeys()) {
+				objectMapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS,
+						true);
+			}
+			return objectMapper;
 		}
 
 		@Bean

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -64,6 +64,7 @@ server.tomcat.max-threads = 0 # number of threads in protocol handler
 
 # SPRING MVC (HttpMapperProperties)
 http.mappers.json-pretty-print=false # pretty print JSON
+http.mappers.json-sort-keys=falose # sort keys
 spring.view.prefix= # MVC view prefix
 spring.view.suffix= # ... and suffix
 spring.resources.cache-period= # cache timeouts in headers sent to browser