Allow @JsonMerge with Custom List

release-notes/VERSION-2.x

@@ -16,6 +16,9 @@ Project: jackson-databind
 #4790: Fix `@JsonAnySetter` issue with "setter" method (related to #4639)
  (reported by @bsa01)
  (fix by Joo-Hyuk K)
+ #4783 Possibly wrong behavior of @JsonMerge
+ (reported by @nlisker)
+ (fix by Joo-Hyuk K)
 
 2.18.1 (28-Oct-2024)
 

src/main/java/com/fasterxml/jackson/databind/deser/BasicDeserializerFactory.java

@@ -824,13 +824,7 @@ public JsonDeserializer<?> createCollectionDeserializer(DeserializationContext c
         if (deser == null) {
             if (type.isInterface() || type.isAbstract()) {
                 CollectionType implType = _mapAbstractCollectionType(type, config);
-                if (implType == null) {
-                    // [databind#292]: Actually, may be fine, but only if polymorphich deser enabled
-                    if (type.getTypeHandler() == null) {
-                        throw new IllegalArgumentException("Cannot find a deserializer for non-concrete Collection type "+type);
-                    }
-                    deser = AbstractDeserializer.constructForNonPOJO(beanDesc);
-                } else {
+                if (implType != null) {
                     type = implType;
                     // But if so, also need to re-check creators...
                     beanDesc = config.introspectForCreation(type);
@@ -972,9 +966,9 @@ public JsonDeserializer<?> createMapDeserializer(DeserializationContext ctxt,
              */
             if (deser == null) {
                 if (type.isInterface() || type.isAbstract()) {
-                    MapType fallback = _mapAbstractMapType(type, config);
-                    if (fallback != null) {
-                        type = (MapType) fallback;
+                    MapType implType = _mapAbstractMapType(type, config);
+                    if (implType != null) {
+                        type = (MapType) implType;
                         mapClass = type.getRawClass();
                         // But if so, also need to re-check creators...
                         beanDesc = config.introspectForCreation(type);

src/test/java/com/fasterxml/jackson/databind/deser/merge/CustomCollectionMerge4783Test.java

@@ -0,0 +1,148 @@
+package com.fasterxml.jackson.databind.deser.merge;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.annotation.JsonMerge;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.exc.InvalidDefinitionException;
+import com.fasterxml.jackson.databind.testutil.DatabindTestUtil;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+// [databind#4783] Test to verify that JsonMerge also works for custom list
+@SuppressWarnings("serial")
+public class CustomCollectionMerge4783Test
+    extends DatabindTestUtil
+{
+    static class MyArrayListJDK<T> extends ArrayList<T> { }
+
+    static class MergeListJDK {
+        @JsonMerge
+        @JsonProperty
+        public List<String> values = new MyArrayListJDK<>();
+        { values.add("a");}
+    }
+
+    interface MyListCustom<T> extends List<T> { }
+
+    static class MyArrayListCustom<T> extends ArrayList<T> implements MyListCustom<T> { }
+
+    static abstract class MyAbstractStringList extends ArrayList<String> {
+        MyAbstractStringList() { super(); }
+        MyAbstractStringList(int i) { super(); }
+    }
+
+    static class MergeCustomStringList {
+        @JsonMerge
+        @JsonProperty
+        public MyListCustom<String> values = new MyArrayListCustom<>();
+        { values.add("a"); }
+    }
+
+    static class MergeMyCustomLongList {
+        @JsonMerge
+        @JsonProperty
+        public MyListCustom<Long> values = new MyArrayListCustom<>();
+        { values.add(1L); }
+    }
+
+    static class MergeMyCustomPojoList {
+        @JsonMerge
+        @JsonProperty
+        public MyListCustom<CustomPojo> values = new MyArrayListCustom<>();
+        {
+            values.add(CustomPojo.create("a", 1));
+            values.add(CustomPojo.create("b", 2));
+        }
+    }
+
+    // And then non-merging case too
+    static class NonMergeCustomStringList {
+        public MyListCustom<String> values;
+    }
+
+    public static class CustomPojo {
+        public String name;
+        public int age;
+
+        public static CustomPojo create(String name, int age) {
+            CustomPojo pojo = new CustomPojo();
+            pojo.name = name;
+            pojo.age = age;
+            return pojo;
+        }
+    }
+
+    private final ObjectMapper MAPPER = newJsonMapper();
+
+    @Test
+    void testJDKMapperReading() throws Exception {
+        MergeListJDK result = MAPPER.readValue("{\"values\":[\"x\"]}", MergeListJDK.class);
+
+        assertEquals(2, result.values.size());
+        assertTrue(result.values.contains("x"));
+        assertTrue(result.values.contains("a"));
+    }
+
+    @Test
+    void testCustomMapperReading() throws Exception {
+        MergeCustomStringList result = MAPPER.readValue("{\"values\":[\"x\"]}",
+                MergeCustomStringList.class);
+
+        assertEquals(2, result.values.size());
+        assertTrue(result.values.contains("x"));
+        assertTrue(result.values.contains("a"));
+    }
+
+    @Test
+    void testCustomMapperReadingLongArrayList() throws Exception {
+        MergeMyCustomLongList result = MAPPER.readValue("{\"values\":[7]}",
+                MergeMyCustomLongList.class);
+
+        assertEquals(2, result.values.size());
+        assertTrue(result.values.contains(1L));
+        assertTrue(result.values.contains(7L));
+    }
+
+    @Test
+    void testCustomMapperReadingPojoArrayList() throws Exception {
+        MergeMyCustomPojoList result = MAPPER.readValue("{\"values\":[{\"name\":\"c\",\"age\":3}]}",
+                MergeMyCustomPojoList.class);
+
+        assertEquals(3, result.values.size());
+    }
+
+    // // // And then failure cases
+
+    // Fail can't construct Collection interface unless there's maaping
+    @Test
+    void failNonMergeInterfaceList() throws Exception {
+        try {
+            MAPPER.readValue("{\"values\":[\"x\"]}", NonMergeCustomStringList.class);
+            fail("Should not pass");
+        } catch (InvalidDefinitionException e) {
+            verifyException(e, String.format(
+                    "Cannot construct instance of `%s` (no Creators",
+                    MyListCustom.class.getName()));
+        }
+    }
+
+    // Fail can't construct abstract types
+    @Test
+    void failNonMergeAbstractList() throws Exception {
+        try {
+            MAPPER.readValue("[]", MyAbstractStringList.class);
+            fail("Should not pass");
+        } catch (InvalidDefinitionException e) {
+            verifyException(e, String.format(
+                    "Cannot construct instance of `%s` (no Creators",
+                    MyAbstractStringList.class.getName()));
+        }
+    }
+}