Builder Deserialization with Type Binding (#921)

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

@@ -198,6 +198,18 @@ public enum MapperFeature implements ConfigFeature
      */
     USE_STATIC_TYPING(false),
 
+    /**
+     * Feature that enables inferring builder type bindings from the value type
+     * being deserialized. This requires that the generic type declaration on
+     * the value type match that on the builder exactly.
+     *<p>
+     * Feature is disabled by default which means that deserialization does
+     * not support deserializing types via builders with type parameters.
+     *<p>
+     * See: https://github.com/FasterXML/jackson-databind/issues/921
+     */
+    INFER_BUILDER_TYPE_BINDINGS(false),
+
     /*
     /******************************************************
     /* View-related features

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

@@ -138,12 +138,18 @@ public JsonDeserializer<Object> createBeanDeserializer(DeserializationContext ct
     }
 
     @Override
-    public JsonDeserializer<Object> createBuilderBasedDeserializer(DeserializationContext ctxt,
-            JavaType valueType, BeanDescription beanDesc, Class<?> builderClass)
-                    throws JsonMappingException
+    public JsonDeserializer<Object> createBuilderBasedDeserializer(
+            DeserializationContext ctxt, JavaType valueType, BeanDescription beanDesc,
+            Class<?> builderClass)
+        throws JsonMappingException
     {
         // First: need a BeanDescription for builder class
-        JavaType builderType = ctxt.constructType(builderClass);
+        JavaType builderType;
+        if (ctxt.isEnabled(MapperFeature.INFER_BUILDER_TYPE_BINDINGS)) {
+            builderType = ctxt.getTypeFactory().constructParametricType(builderClass, valueType.getBindings());
+        } else {
+            builderType = ctxt.constructType(builderClass);
+        }
         BeanDescription builderDesc = ctxt.getConfig().introspectForBuilder(builderType);
         return buildBuilderBasedDeserializer(ctxt, valueType, builderDesc);
     }

src/main/java/com/fasterxml/jackson/databind/type/TypeFactory.java

@@ -894,7 +894,29 @@ public JavaType constructParametricType(Class<?> parametrized, Class<?>... param
      */
     public JavaType constructParametricType(Class<?> rawType, JavaType... parameterTypes)
     {
-        return _fromClass(null, rawType, TypeBindings.create(rawType, parameterTypes));
+        return constructParametricType(rawType, TypeBindings.create(rawType, parameterTypes));
+    }
+
+    /**
+     * Factory method for constructing {@link JavaType} that
+     * represents a parameterized type. The type's parameters are
+     * specified as an instance of {@link TypeBindings}. This
+     * is useful if you already have the type's parameters such
+     * as those found on {@link JavaType}. For example, you could
+     * call
+     * <pre>
+     *   return TypeFactory.constructParametricType(ArrayList.class, javaType.getBindings());
+     * </pre>
+     * This effectively applies the parameterized types from one
+     * {@link JavaType} to another class.
+     *
+     * @param rawType Actual type-erased type
+     * @param parameterTypes Type bindings for the raw type
+     * @since 3.0
+     */
+    public JavaType constructParametricType(Class<?> rawType, TypeBindings parameterTypes)
+    {
+        return _fromClass(null, rawType, parameterTypes);
     }
 
     /*

src/test/java/com/fasterxml/jackson/failing/BuilderDeserializationTest921.java → src/test/java/com/fasterxml/jackson/databind/deser/builder/BuilderWithTypeParametersTest.java

@@ -1,13 +1,16 @@
-package com.fasterxml.jackson.failing;
+package com.fasterxml.jackson.databind.deser.builder;
 
-import java.util.List;
-
-import com.fasterxml.jackson.annotation.*;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.type.TypeReference;
-import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.databind.BaseMapTest;
+import com.fasterxml.jackson.databind.MapperFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import java.util.LinkedHashMap;
+import java.util.List;
 
-public class BuilderDeserializationTest921
+public class BuilderWithTypeParametersTest
     extends BaseMapTest
 {
     public static class MyPOJO {
@@ -77,15 +80,27 @@ public MyGenericPOJOWithCreator<T> build() {
       }
     }
 
-    public void testWithBuilder() throws Exception {
+    public void testWithBuilderInferringBindings() throws Exception {
+        final ObjectMapper mapper = new ObjectMapper();
+        mapper.enable(MapperFeature.INFER_BUILDER_TYPE_BINDINGS);
+        final String json = aposToQuotes("{ 'data': [ { 'x': 'x', 'y': 'y' } ] }");
+        final MyGenericPOJO<MyPOJO> deserialized =
+                mapper.readValue(json, new TypeReference<MyGenericPOJO<MyPOJO>>() {});
+        assertEquals(1, deserialized.data.size());
+        Object ob = deserialized.data.get(0);
+        assertNotNull(ob);
+        assertEquals(MyPOJO.class, ob.getClass());
+    }
+
+    public void testWithBuilderWithoutInferringBindings() throws Exception {
       final ObjectMapper mapper = new ObjectMapper();
       final String json = aposToQuotes("{ 'data': [ { 'x': 'x', 'y': 'y' } ] }");
       final MyGenericPOJO<MyPOJO> deserialized =
           mapper.readValue(json, new TypeReference<MyGenericPOJO<MyPOJO>>() {});
       assertEquals(1, deserialized.data.size());
       Object ob = deserialized.data.get(0);
       assertNotNull(ob);
-      assertEquals(MyPOJO.class, ob.getClass());
+      assertEquals(LinkedHashMap.class, ob.getClass());
     }
 
     public void testWithCreator() throws Exception {

src/test/java/com/fasterxml/jackson/databind/type/TestTypeFactory.java

@@ -175,13 +175,27 @@ public void testParametricTypes()
         assertEquals(t, t2.containedType(1));
         assertNull(t2.containedType(2));
 
-        // and then custom generic type as well
+        // Then using TypeBindings
+        JavaType t3 = tf.constructParametricType(HashSet.class, t.getBindings()); // HashSet<String>
+        assertEquals(CollectionType.class, t3.getClass());
+        assertEquals(1, t3.containedTypeCount());
+        assertEquals(strC, t3.containedType(0));
+        assertNull(t3.containedType(1));
+
+        // Then custom generic type as well
         JavaType custom = tf.constructParametricType(SingleArgGeneric.class, String.class);
         assertEquals(SimpleType.class, custom.getClass());
         assertEquals(1, custom.containedTypeCount());
         assertEquals(strC, custom.containedType(0));
         assertNull(custom.containedType(1));
 
+        // and then custom generic type from TypeBindings
+        JavaType custom2 = tf.constructParametricType(SingleArgGeneric.class, t.getBindings());
+        assertEquals(SimpleType.class, custom2.getClass());
+        assertEquals(1, custom2.containedTypeCount());
+        assertEquals(strC, custom2.containedType(0));
+        assertNull(custom2.containedType(1));
+
         // And finally, ensure that we can't create invalid combinations
         try {
             // Maps must take 2 type parameters, not just one