Add configuration option to EventJsonLayoutBaseFactory to flatten MDC

dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/EventJsonLayoutBaseFactory.java

@@ -31,6 +31,11 @@
  * <td>(empty)</td>
  * <td>Set of MDC keys which should be included in the JSON map. By default includes everything.</td>
  * </tr>
+ * <tr>
+ * <td>{@code flattenMdc}</td>
+ * <td>{@code false}</td>
+ * <td>Whether the MDC should be included under the key "mdc" or flattened into the map.</td>
+ * </tr>
  * </table>
  */
 @JsonTypeName("json")
@@ -41,6 +46,7 @@ public class EventJsonLayoutBaseFactory extends AbstractJsonLayoutBaseFactory<IL
         EventAttribute.EXCEPTION, EventAttribute.TIMESTAMP);
 
     private Set<String> includesMdcKeys = ImmutableSet.of();
+    private boolean flattenMdc = false;
 
     @JsonProperty
     public EnumSet<EventAttribute> getIncludes() {
@@ -62,12 +68,22 @@ public void setIncludesMdcKeys(Set<String> includesMdcKeys) {
         this.includesMdcKeys = includesMdcKeys;
     }
 
+    @JsonProperty
+    public boolean isFlattenMdc() {
+        return flattenMdc;
+    }
+
+    @JsonProperty
+    public void setFlattenMdc(boolean flattenMdc) {
+        this.flattenMdc = flattenMdc;
+    }
+
     @Override
     @SuppressWarnings("unchecked")
     public LayoutBase<ILoggingEvent> build(LoggerContext context, TimeZone timeZone) {
         final EventJsonLayout jsonLayout = new EventJsonLayout(createDropwizardJsonFormatter(),
             createTimestampFormatter(timeZone), createThrowableProxyConverter(), includes, getCustomFieldNames(),
-            getAdditionalFields(), includesMdcKeys);
+            getAdditionalFields(), includesMdcKeys, flattenMdc);
         jsonLayout.setContext(context);
         return jsonLayout;
     }

dropwizard-json-logging/src/main/java/io/dropwizard/logging/json/layout/EventJsonLayout.java

@@ -28,18 +28,20 @@ public class EventJsonLayout extends AbstractJsonLayout<ILoggingEvent> {
     private final Map<String, String> customFieldNames;
 
     private ImmutableSet<String> includesMdcKeys;
+    private final boolean flattenMdc;
 
     public EventJsonLayout(JsonFormatter jsonFormatter, TimestampFormatter timestampFormatter,
                            ThrowableHandlingConverter throwableProxyConverter, Set<EventAttribute> includes,
                            Map<String, String> customFieldNames, Map<String, Object> additionalFields,
-                           Set<String> includesMdcKeys) {
+                           Set<String> includesMdcKeys, boolean flattenMdc) {
         super(jsonFormatter);
         this.timestampFormatter = timestampFormatter;
         this.additionalFields = ImmutableMap.copyOf(additionalFields);
         this.customFieldNames = ImmutableMap.copyOf(customFieldNames);
         this.throwableProxyConverter = throwableProxyConverter;
         this.includes = ImmutableSet.copyOf(includes);
         this.includesMdcKeys = ImmutableSet.copyOf(includesMdcKeys);
+        this.flattenMdc = flattenMdc;
     }
 
     @Override
@@ -56,18 +58,23 @@ public void stop() {
 
     @Override
     protected Map<String, Object> toJsonMap(ILoggingEvent event) {
-        return new MapBuilder(timestampFormatter, customFieldNames, additionalFields, 16)
+        final MapBuilder mapBuilder = new MapBuilder(timestampFormatter, customFieldNames, additionalFields, 16)
             .addTimestamp("timestamp", isIncluded(EventAttribute.TIMESTAMP), event.getTimeStamp())
             .add("level", isIncluded(EventAttribute.LEVEL), String.valueOf(event.getLevel()))
             .add("thread", isIncluded(EventAttribute.THREAD_NAME), event.getThreadName())
-            .add("mdc", isIncluded(EventAttribute.MDC), filterMdc(event.getMDCPropertyMap()))
             .add("logger", isIncluded(EventAttribute.LOGGER_NAME), event.getLoggerName())
             .add("message", isIncluded(EventAttribute.MESSAGE), event.getFormattedMessage())
             .add("context", isIncluded(EventAttribute.CONTEXT_NAME), event.getLoggerContextVO().getName())
             .add("version", jsonProtocolVersion != null, jsonProtocolVersion)
             .add("exception", isIncluded(EventAttribute.EXCEPTION) && event.getThrowableProxy() != null,
-                throwableProxyConverter.convert(event))
-            .build();
+                 throwableProxyConverter.convert(event));
+        final boolean includeMdc = isIncluded(EventAttribute.MDC);
+        if (flattenMdc) {
+            filterMdc(event.getMDCPropertyMap()).forEach((k,v) -> mapBuilder.add(k, includeMdc, v));
+        } else {
+            mapBuilder.add("mdc", includeMdc, filterMdc(event.getMDCPropertyMap()));
+        }
+        return mapBuilder.build();
     }
 
     private Map<String, String> filterMdc(Map<String, String> mdcPropertyMap) {

dropwizard-json-logging/src/test/java/io/dropwizard/logging/json/LayoutIntegrationTests.java

@@ -74,6 +74,7 @@ public void testDeserializeJson() throws Exception {
             EventAttribute.LOGGER_NAME,
             EventAttribute.EXCEPTION,
             EventAttribute.TIMESTAMP);
+        assertThat(factory.isFlattenMdc()).isTrue();
         assertThat(factory.getCustomFieldNames()).containsOnly(entry("timestamp", "@timestamp"));
         assertThat(factory.getAdditionalFields()).containsOnly(entry("service-name", "user-service"),
             entry("service-build", 218));

dropwizard-json-logging/src/test/java/io/dropwizard/logging/json/layout/EventJsonLayoutTest.java

@@ -41,7 +41,7 @@ public class EventJsonLayoutTest {
         EventAttribute.THREAD_NAME, EventAttribute.MDC, EventAttribute.LOGGER_NAME, EventAttribute.MESSAGE,
         EventAttribute.EXCEPTION, EventAttribute.TIMESTAMP);
     private EventJsonLayout eventJsonLayout = new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter,
-        includes, ImmutableMap.of(), ImmutableMap.of(), ImmutableSet.of());
+        includes, ImmutableMap.of(), ImmutableMap.of(), ImmutableSet.of(), false);
 
     @Before
     public void setUp() {
@@ -109,7 +109,7 @@ public void testLogVersion() {
     public void testReplaceFieldName() {
         Map<String, Object> map = new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, includes,
             ImmutableMap.of("timestamp", "@timestamp", "message", "@message"), ImmutableMap.of(),
-            ImmutableSet.of())
+            ImmutableSet.of(), false)
             .toJsonMap(event);
         assertThat(map).containsOnly(entry("@timestamp", timestamp),
             entry("thread", "main"),
@@ -123,7 +123,7 @@ public void testReplaceFieldName() {
     public void testAddNewField() {
         Map<String, Object> map = new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, includes,
             ImmutableMap.of(), ImmutableMap.of("serviceName", "userService", "serviceBuild", 207),
-            ImmutableSet.of())
+            ImmutableSet.of(), false)
             .toJsonMap(event);
         assertThat(map).containsOnly(entry("timestamp", timestamp),
             entry("thread", "main"),
@@ -139,7 +139,7 @@ public void testAddNewField() {
     public void testFilterMdc() {
         Map<String, Object> map = new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter, includes,
             ImmutableMap.of(), ImmutableMap.of(),
-            ImmutableSet.of("userId", "orderId")).toJsonMap(event);
+            ImmutableSet.of("userId", "orderId"), false).toJsonMap(event);
         assertThat(map).containsOnly(entry("timestamp", timestamp),
             entry("thread", "main"),
             entry("level", "INFO"),
@@ -148,6 +148,20 @@ public void testFilterMdc() {
             entry("mdc", ImmutableMap.of("userId", "18", "orderId", "24")));
     }
 
+    @Test
+    public void testFlattensMdcMap() {
+        Map<String, Object> map = new EventJsonLayout(jsonFormatter, timestampFormatter, throwableProxyConverter,
+            includes, ImmutableMap.of(), ImmutableMap.of(), ImmutableSet.of(), true).toJsonMap(event);
+        assertThat(map).containsOnly(entry("timestamp", timestamp),
+                                     entry("thread", "main"),
+                                     entry("level", "INFO"),
+                                     entry("logger", logger),
+                                     entry("message", message),
+                                     entry("userId", "18"),
+                                     entry("serviceId", "19"),
+                                     entry("orderId", "24"));
+    }
+
     @Test
     public void testStartThrowableConverter() {
         eventJsonLayout.start();

dropwizard-json-logging/src/test/resources/yaml/json-log.yml

@@ -18,4 +18,5 @@ layout:
     service-name: "user-service"
     service-build: 218
   includesMdcKeys: [userId]
+  flattenMdc: true