Implement #679

release-notes/VERSION

@@ -10,6 +10,7 @@ Project: jackson-databind
 #348: ObjectMapper.valueToTree does not work with @JsonRawValue
  (reported by Chris P, pimlottc@github)
 #649: Make `BeanDeserializer` use new `parser.nextFieldName()` and `.hasTokenId()` methods
+#679: Add `isEmpty()` implementation for `JsonNode` serializers
 #696: Copy constructor does not preserve `_injectableValues`
  (reported by Charles A)
 #700: Cannot Change Default Abstract Type Mapper from LinkedHashMap

src/main/java/com/fasterxml/jackson/databind/JsonNode.java

@@ -37,8 +37,8 @@
  * and {@link ObjectMapper#treeAsTokens(TreeNode)}
  */
 public abstract class JsonNode
-    implements TreeNode, Iterable<JsonNode>,
-        JsonSerializable // since 2.5; bit tricky if anyone is sub-classing but...
+    extends JsonSerializable.Base // i.e. implements JsonSerializable
+    implements TreeNode, Iterable<JsonNode>
 {
     /*
     /**********************************************************

src/main/java/com/fasterxml/jackson/databind/JsonSerializable.java

@@ -15,9 +15,9 @@
  * so -- if class is a bean, it can be serialized without
  * implementing this interface.
  *<p>
- * NOTE: Jackson 2.0 added another method (from former "JsonSerializableWithType"),
- * which is required for proper handling of case where additional type information
- * is needed.
+ * Note that while it is possible to just directly implement {@link JsonSerializable},
+ * actual implementations are strongly recommended to instead extend
+ * {@link JsonSerializable.Base}.
  */
 public interface JsonSerializable
 {
@@ -44,4 +44,23 @@ public interface JsonSerializable
      */
     public void serializeWithType(JsonGenerator gen, SerializerProvider serializers,
             TypeSerializer typeSer) throws IOException;
+
+    /**
+     * Base class with minimal implementation, as well as couple of extension methods
+     * that core Jackson databinding makes use of.
+     * Use of this base class is strongly recommended over directly implementing
+     * {@link JsonSerializable}.
+     *
+     * @since 2.6
+     */
+    public static class Base
+    {
+        /**
+         * Method that may be called on instance to determine if it is considered
+         * "empty" for purposes of serialization filtering or not.
+         */
+        public boolean isEmpty(SerializerProvider serializers) {
+            return false;
+        }
+    }
 }

src/main/java/com/fasterxml/jackson/databind/node/ArrayNode.java

@@ -43,6 +43,17 @@ public ArrayNode deepCopy()
         return ret;
     }
 
+    /*
+    /**********************************************************
+    /* Overrides for JsonSerializable.Base
+    /**********************************************************
+     */
+
+    @Override
+    public boolean isEmpty(SerializerProvider serializers) {
+        return _children.isEmpty();
+    }
+
     /*
     /**********************************************************
     /* Implementation of core JsonNode API

src/main/java/com/fasterxml/jackson/databind/node/ObjectNode.java

@@ -1,8 +1,7 @@
 package com.fasterxml.jackson.databind.node;
 
 import com.fasterxml.jackson.core.*;
-import com.fasterxml.jackson.databind.JsonNode;
-import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
 import com.fasterxml.jackson.databind.util.RawValue;
 
@@ -61,6 +60,17 @@ public ObjectNode deepCopy()
         return ret;
     }
 
+    /*
+    /**********************************************************
+    /* Overrides for JsonSerializable.Base
+    /**********************************************************
+     */
+
+    @Override
+    public boolean isEmpty(SerializerProvider serializers) {
+        return _children.isEmpty();
+    }
+
     /*
     /**********************************************************
     /* Implementation of core JsonNode API

src/main/java/com/fasterxml/jackson/databind/ser/std/SerializableSerializer.java

@@ -37,14 +37,27 @@ public class SerializableSerializer
     protected SerializableSerializer() { super(JsonSerializable.class); }
 
     @Override
-    public void serialize(JsonSerializable value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
-        value.serialize(jgen, provider);
+    public boolean isEmpty(SerializerProvider serializers, JsonSerializable value) {
+        if (value instanceof JsonSerializable.Base) {
+            return ((JsonSerializable.Base) value).isEmpty(serializers);
+        }
+        return false;
+    }
+
+    @Deprecated
+    public boolean isEmpty(JsonSerializable value) {
+        return isEmpty(null, value);
+    }
+
+    @Override
+    public void serialize(JsonSerializable value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
+        value.serialize(gen, serializers);
     }
 
     @Override
-    public final void serializeWithType(JsonSerializable value, JsonGenerator jgen, SerializerProvider provider,
+    public final void serializeWithType(JsonSerializable value, JsonGenerator gen, SerializerProvider serializers,
             TypeSerializer typeSer) throws IOException {
-        value.serializeWithType(jgen, provider, typeSer);
+        value.serializeWithType(gen, serializers, typeSer);
     }
 
     @Override

src/test/java/com/fasterxml/jackson/databind/node/TestObjectNode.java

@@ -4,6 +4,7 @@
 import java.util.*;
 
 import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonValue;
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
@@ -37,6 +38,15 @@ public DataImpl(JsonNode n) {
         public ObjectNode value() { return root; }
         */
     }
+
+    static class ObNodeWrapper {
+        @JsonInclude(JsonInclude.Include.NON_EMPTY)
+        public ObjectNode node;
+
+        public ObNodeWrapper(ObjectNode n) {
+            node = n;
+        }
+    }
 
     /*
     /**********************************************************
@@ -366,4 +376,13 @@ public void testSimplePath() throws Exception
         assertTrue(rnode.isObject());
         assertEquals(3, rnode.path("a").intValue());
     }
+
+    public void testNonEmptySerialization() throws Exception
+    {
+        ObNodeWrapper w = new ObNodeWrapper(MAPPER.createObjectNode()
+                .put("a", 3));
+        assertEquals("{\"node\":{\"a\":3}}", MAPPER.writeValueAsString(w));
+        w = new ObNodeWrapper(MAPPER.createObjectNode());
+        assertEquals("{}", MAPPER.writeValueAsString(w));
+    }
 }