feat: Introduce Option.ACCEPT_SINGLE_VALUE_AS_ARRAY

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### `jsonschema-generator`
+#### Added
+- new `Option.ACCEPT_SINGLE_VALUE_AS_ARRAY` to support Jackson `DeserializationFeature` of the same name, i.e., when an array type is declared, an instance of a single item should also be accepted by the schema
+
 #### Changed
 - consider `Boolean` values as valid in `const`/`enum` (i.e., no longer ignore them)
 

jsonschema-examples/src/main/java/com/github/victools/jsonschema/examples/SingleArrayItemExample.java

@@ -19,6 +19,7 @@
 import com.fasterxml.classmate.ResolvedType;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.github.victools.jsonschema.generator.MemberScope;
+import com.github.victools.jsonschema.generator.Option;
 import com.github.victools.jsonschema.generator.OptionPreset;
 import com.github.victools.jsonschema.generator.SchemaGenerationContext;
 import com.github.victools.jsonschema.generator.SchemaGenerator;
@@ -42,22 +43,13 @@ public class SingleArrayItemExample implements SchemaGenerationExampleInterface
     @Override
     public ObjectNode generateSchema() {
         SchemaGeneratorConfigBuilder configBuilder = new SchemaGeneratorConfigBuilder(SchemaVersion.DRAFT_2020_12, OptionPreset.PLAIN_JSON);
-        configBuilder.forFields()
-                .withTargetTypeOverridesResolver(this::acceptSingleValueAsArray);
+        configBuilder.with(Option.ACCEPT_SINGLE_VALUE_AS_ARRAY);
         SchemaGeneratorConfig config = configBuilder.build();
         SchemaGenerator generator = new SchemaGenerator(config);
         return generator.generateSchema(Example.class);
     }
 
-    private List<ResolvedType> acceptSingleValueAsArray(MemberScope<?, ?> scope) {
-        if (scope.isContainerType() && !scope.isFakeContainerItemScope()) {
-            return Arrays.asList(scope.getContainerItemType(), scope.getType());
-        }
-        return null;
-    }
-
     static class Example {
-        @NotNull
         public List<ArrayItem> someArray;
     }
 

jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/Option.java

@@ -26,6 +26,7 @@
 import com.github.victools.jsonschema.generator.impl.module.MethodExclusionModule;
 import com.github.victools.jsonschema.generator.impl.module.SimpleTypeModule;
 import com.github.victools.jsonschema.generator.impl.module.SimplifiedOptionalModule;
+import com.github.victools.jsonschema.generator.impl.module.SingleValueAsArrayModule;
 import java.util.Collections;
 import java.util.Set;
 import java.util.function.Supplier;
@@ -222,6 +223,14 @@ public enum Option {
      * @since 4.11.0
      */
     MAP_VALUES_AS_ADDITIONAL_PROPERTIES(AdditionalPropertiesModule::forMapValues, null),
+    /**
+     * Whether each property with a container/{@link java.util.Collection Collection} type should also allow for a single collection item to be
+     * provided instead of an array. This corresponds to the Jackson
+     * {@link com.fasterxml.jackson.databind.DeserializationFeature#ACCEPT_SINGLE_VALUE_AS_ARRAY ACCEPT_SINGLE_VALUE_AS_ARRAY} feature.
+     *
+     * @since 4.36.0
+     */
+    ACCEPT_SINGLE_VALUE_AS_ARRAY(SingleValueAsArrayModule::new, null),
     /**
      * Whether allowed values should always be included in an {@link SchemaKeyword#TAG_ENUM "enum"} keyword. If there is exactly one allowed value, it
      * will otherwise be represented by a {@link SchemaKeyword#TAG_CONST "const"} keyword instead.

jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/module/SingleValueAsArrayModule.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2024 VicTools.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.github.victools.jsonschema.generator.impl.module;
+
+import com.fasterxml.classmate.ResolvedType;
+import com.github.victools.jsonschema.generator.MemberScope;
+import com.github.victools.jsonschema.generator.Module;
+import com.github.victools.jsonschema.generator.SchemaGeneratorConfigBuilder;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Default module being included if {@code Option.ACCEPT_SINGLE_VALUE_AS_ARRAY} is enabled.
+ *
+ * @since 4.36.0
+ */
+public class SingleValueAsArrayModule implements Module {
+
+    /**
+     * Allow a container's item type as single instance alternative to an array, or return null for non-containers.
+     *
+     * @param scope targeted field/method
+     * @return collection containing both the container's item type and the container type as such, or null
+     */
+    private static List<ResolvedType> acceptSingleValueAsArray(MemberScope<?, ?> scope) {
+        if (scope.isContainerType() && !scope.isFakeContainerItemScope()) {
+            return Arrays.asList(scope.getContainerItemType(), scope.getType());
+        }
+        return null;
+    }
+
+    @Override
+    public void applyToConfigBuilder(SchemaGeneratorConfigBuilder builder) {
+        builder.forFields()
+                .withTargetTypeOverridesResolver(SingleValueAsArrayModule::acceptSingleValueAsArray);
+        builder.forMethods()
+                .withTargetTypeOverridesResolver(SingleValueAsArrayModule::acceptSingleValueAsArray);
+    }
+}

jsonschema-generator/src/test/java/com/github/victools/jsonschema/generator/SchemaGeneratorComplexTypesTest.java

@@ -117,7 +117,8 @@ static Stream<Arguments> parametersForTestGenerateSchema() {
                         .withAnchorResolver(scope -> scope.isContainerType() ? null : "#anchor")
                         .withPropertySorter((_prop1, _prop2) -> 0),
                 "for type in general: ");
-        Module methodModule = configBuilder -> populateConfigPart(configBuilder.with(Option.FIELDS_DERIVED_FROM_ARGUMENTFREE_METHODS)
+        Module methodModule = configBuilder -> populateConfigPart(configBuilder.with(Option.FIELDS_DERIVED_FROM_ARGUMENTFREE_METHODS,
+                Option.ACCEPT_SINGLE_VALUE_AS_ARRAY)
                 .forMethods(), "looked-up from method: ");
         Module fieldModule = configBuilder -> populateConfigPart(configBuilder.with(Option.INLINE_ALL_SCHEMAS).forFields(), "looked-up from field: ");
         Module enumToStringModule = configBuilder -> configBuilder.with(Option.FLATTENED_ENUMS_FROM_TOSTRING);

jsonschema-generator/src/test/resources/com/github/victools/jsonschema/generator/testclass1-JAVA_OBJECT-methodattributes.json

@@ -6,10 +6,16 @@
             "const": 5
         },
         "genericArray": {
-            "type": "array",
-            "items": {
-                "type": "string"
-            }
+            "anyOf": [
+                {
+                    "type": "string"
+                }, {
+                    "type": "array",
+                    "items": {
+                        "type": "string"
+                    }
+                }
+            ]
         },
         "genericValue": {
             "type": ["string", "null"],