Enhance StdNodeBasedDeserializer to facilitate usage with `ObjectMa…

…pper#readerForUpdating` (#3860)

src/main/java/com/fasterxml/jackson/databind/deser/std/StdNodeBasedDeserializer.java

@@ -61,6 +61,19 @@ public void resolve(DeserializationContext ctxt) throws JsonMappingException {
 
     public abstract T convert(JsonNode root, DeserializationContext ctxt) throws IOException;
 
+    /**
+     * Facilitates usage with {@link ObjectMapper#readerForUpdating(Object)} and {@link #deserialize(JsonParser, DeserializationContext, Object)}
+     * by eliminating the need to manually convert the value to a {@link JsonNode}.
+     *
+     * If this method is not overridden, it falls back to the behavior of {@link #convert(JsonNode, DeserializationContext)}.
+     *
+     * @since 2.15
+     */
+    public T convert(JsonNode root, DeserializationContext ctxt, T newValue) throws IOException {
+        ctxt.handleBadMerge(this);
+        return convert(root, ctxt);
+    }
+
     /*
     /**********************************************************
     /* JsonDeserializer impl
@@ -73,6 +86,18 @@ public T deserialize(JsonParser jp, DeserializationContext ctxt) throws IOExcept
         return convert(n, ctxt);
     }
 
+    /**
+     *
+     * Added to support {@link #convert(JsonNode, DeserializationContext, Object)}
+     *
+     * @since 2.15
+     */
+    @Override
+    public T deserialize(JsonParser jp, DeserializationContext ctxt, T newValue) throws IOException {
+        JsonNode n = (JsonNode) _treeDeserializer.deserialize(jp, ctxt);
+        return convert(n, ctxt, newValue);
+    }
+
     @Override
     public Object deserializeWithType(JsonParser jp, DeserializationContext ctxt,
             TypeDeserializer td)

src/test/java/com/fasterxml/jackson/databind/convert/TestUpdateViaObjectReader.java

@@ -9,6 +9,7 @@
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
 import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
+import com.fasterxml.jackson.databind.deser.std.StdNodeBasedDeserializer;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 
 import static org.junit.Assert.assertArrayEquals;
@@ -115,6 +116,61 @@ public AnimalWrapper deserialize(JsonParser json, DeserializationContext context
         }
     }
 
+    @JsonDeserialize(using = Custom3814DeserializerA.class)
+    static class Bean3814A {
+        public int age;
+
+        public Bean3814A(int age) {
+            this.age = age;
+        }
+
+        public void updateTo(JsonNode root) {
+            age = root.get("age").asInt();
+        }
+    }
+
+    static class Custom3814DeserializerA extends StdNodeBasedDeserializer<Bean3814A> {
+        public Custom3814DeserializerA() {
+            super(Bean3814A.class);
+        }
+
+        @Override
+        public Bean3814A convert(JsonNode root, DeserializationContext ctxt) throws IOException {
+            return null;
+        }
+
+        @Override
+        public Bean3814A convert(JsonNode root, DeserializationContext ctxt, Bean3814A oldValue) throws IOException {
+            oldValue.updateTo(root);
+            return oldValue;
+        }
+    }
+
+    @JsonDeserialize(using = Custom3814DeserializerB.class)
+    static class Bean3814B {
+        public int age;
+
+        public Bean3814B(int age) {
+            this.age = age;
+        }
+
+        public void updateTo(JsonNode root) {
+            age = root.get("age").asInt();
+        }
+    }
+
+    static class Custom3814DeserializerB extends StdNodeBasedDeserializer<Bean3814B> {
+        public Custom3814DeserializerB() {
+            super(Bean3814B.class);
+        }
+
+        @Override
+        public Bean3814B convert(JsonNode root, DeserializationContext ctxt) throws IOException {
+            return null;
+        }
+
+    }
+
     /*
     /********************************************************
     /* Test methods
@@ -233,7 +289,7 @@ public void testUpdatingWithViews() throws Exception
     }
 
     // [databind#744]
-    public void testIssue744() throws IOException
+    public void testIssue744() throws Exception
     {
         ObjectMapper mapper = new ObjectMapper();
         SimpleModule module = new SimpleModule();
@@ -274,7 +330,7 @@ public void testIssue744() throws IOException
     }
 
     // [databind#1831]
-    public void test1831UsingNode() throws IOException {
+    public void test1831UsingNode() throws Exception {
         String catJson = MAPPER.writeValueAsString(new Cat());
         JsonNode jsonNode = MAPPER.readTree(catJson);
         AnimalWrapper optionalCat = new AnimalWrapper();
@@ -283,10 +339,38 @@ public void test1831UsingNode() throws IOException {
         assertSame(optionalCat, result);
     }
 
-    public void test1831UsingString() throws IOException {
+    public void test1831UsingString() throws Exception {
         String catJson = MAPPER.writeValueAsString(new Cat());
         AnimalWrapper optionalCat = new AnimalWrapper();
         AnimalWrapper result = MAPPER.readerForUpdating(optionalCat).readValue(catJson);
         assertSame(optionalCat, result);
     }
+
+    // [databind#3814]
+    public void testReaderForUpdating3814() throws Exception {
+        // Arrange
+        JsonNode root = MAPPER.readTree(a2q("{'age': 30 }"));
+        Bean3814A obj = new Bean3814A(25);
+
+        // Act
+        Bean3814A newObj = MAPPER.readerForUpdating(obj).readValue(root);
+
+        // Assert
+        assertSame(obj, newObj);
+        assertEquals(30, newObj.age);
+    }
+
+    // [databind#3814]
+    public void testReaderForUpdating3814DoesNotOverride() throws Exception {
+        // Arrange
+        JsonNode root = MAPPER.readTree(a2q("{'age': 30 }"));
+        Bean3814B obj = new Bean3814B(25);
+
+        // Act
+        Bean3814B newObj = MAPPER.readerForUpdating(obj).readValue(root);
+
+        // Assert
+        assertNotSame(obj, newObj);
+        assertNull(newObj);
+    }
 }