chore(example): show-case reflection based subtype resolution (#356)

jsonschema-examples/pom.xml

@@ -64,6 +64,11 @@
             <groupId>io.swagger.core.v3</groupId>
             <artifactId>swagger-annotations</artifactId>
         </dependency>
+        <dependency>
+            <groupId>io.github.classgraph</groupId>
+            <artifactId>classgraph</artifactId>
+            <version>4.8.149</version>
+        </dependency>
     </dependencies>
 
     <build>

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

@@ -0,0 +1,122 @@
+/*
+ * Copyright 2023 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.examples;
+
+import com.fasterxml.classmate.ResolvedType;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+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;
+import com.github.victools.jsonschema.generator.SchemaGeneratorConfig;
+import com.github.victools.jsonschema.generator.SchemaGeneratorConfigBuilder;
+import com.github.victools.jsonschema.generator.SchemaVersion;
+import com.github.victools.jsonschema.generator.SubtypeResolver;
+import com.github.victools.jsonschema.generator.TypeContext;
+import io.github.classgraph.ClassGraph;
+import io.github.classgraph.ClassInfo;
+import io.github.classgraph.ClassInfoList;
+import io.github.classgraph.ScanResult;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * Example created to show-case generic subtype look-up.
+ * <br/>
+ * Using classgraph for determining type hierarchy.
+ */
+public class SubtypeLookUpExample implements SchemaGenerationExampleInterface {
+
+    @Override
+    public ObjectNode generateSchema() {
+        SchemaGeneratorConfigBuilder configBuilder = new SchemaGeneratorConfigBuilder(SchemaVersion.DRAFT_2020_12, OptionPreset.PLAIN_JSON);
+        configBuilder.with(Option.DEFINITIONS_FOR_ALL_OBJECTS, Option.DEFINITIONS_FOR_MEMBER_SUPERTYPES);
+        configBuilder.forTypesInGeneral()
+                .withSubtypeResolver(new ClassGraphSubtypeResolver());
+        SchemaGeneratorConfig config = configBuilder.build();
+        SchemaGenerator generator = new SchemaGenerator(config);
+        return generator.generateSchema(Example.class);
+    }
+
+    /**
+     * Simple implementation of a reflection based subtype resolver, considering only subtypes from a certain package.
+     */
+    static class ClassGraphSubtypeResolver implements SubtypeResolver {
+
+        private final ClassGraph classGraphConfig;
+        private ScanResult scanResult;
+
+        ClassGraphSubtypeResolver() {
+            this.classGraphConfig = new ClassGraph()
+                    .enableClassInfo()
+                    .enableInterClassDependencies()
+                    // in this example, only consider a certain set of potential subtypes
+                    .acceptPackages("com.github.victools.jsonschema.examples");
+        }
+
+        private ScanResult getScanResult() {
+            if (this.scanResult == null) {
+                this.scanResult = this.classGraphConfig.scan();
+            }
+            return this.scanResult;
+        }
+
+        @Override
+        public void resetAfterSchemaGenerationFinished() {
+            if (this.scanResult != null) {
+                this.scanResult.close();
+                this.scanResult = null;
+            }
+        }
+
+        @Override
+        public List<ResolvedType> findSubtypes(ResolvedType declaredType, SchemaGenerationContext context) {
+            if (declaredType.getErasedType() == Object.class) {
+                return null;
+            }
+            ClassInfoList subtypes;
+            if (declaredType.isInterface()) {
+                subtypes = this.getScanResult().getClassesImplementing(declaredType.getErasedType());
+            } else {
+                subtypes = this.getScanResult().getSubclasses(declaredType.getErasedType());
+            }
+            if (!subtypes.isEmpty()) {
+                TypeContext typeContext = context.getTypeContext();
+                return subtypes.loadClasses(true)
+                        .stream()
+                        .map(subclass -> typeContext.resolveSubtype(declaredType, subclass))
+                        .collect(Collectors.toList());
+            }
+            return null;
+        }
+    }
+
+    static class Example {
+        public BaseType declaredAsBaseType;
+    }
+
+    interface BaseType {
+    }
+
+    static class SubType1 implements BaseType {
+        public String text;
+    }
+
+    static class SubType2 implements BaseType {
+        public List<BaseType> nested;
+    }
+}

jsonschema-examples/src/test/java/com/github/victools/jsonschema/examples/ExampleTest.java

@@ -37,7 +37,8 @@ public class ExampleTest {
             IfThenElseExample.class,
             JacksonDescriptionAsTitleExample.class,
             JacksonSubtypeDefinitionExample.class,
-            StrictTypeInfoExample.class
+            StrictTypeInfoExample.class,
+            SubtypeLookUpExample.class
     })
     public void testExample(Class<? extends SchemaGenerationExampleInterface> exampleType) throws Exception {
         SchemaGenerationExampleInterface exampleImplementation = exampleType.getDeclaredConstructor().newInstance();

jsonschema-examples/src/test/resources/com/github/victools/jsonschema/examples/SubtypeLookUpExample-result.json

@@ -0,0 +1,37 @@
+{
+    "$schema" : "https://json-schema.org/draft/2020-12/schema",
+    "$defs" : {
+        "BaseType" : {
+            "anyOf" : [ {
+                "$ref" : "#/$defs/SubType1"
+            }, {
+                "$ref" : "#/$defs/SubType2"
+            } ]
+        },
+        "SubType1" : {
+            "type" : "object",
+            "properties" : {
+                "text" : {
+                    "type" : "string"
+                }
+            }
+        },
+        "SubType2" : {
+            "type" : "object",
+            "properties" : {
+                "nested" : {
+                    "type" : "array",
+                    "items" : {
+                        "$ref" : "#/$defs/BaseType"
+                    }
+                }
+            }
+        }
+    },
+    "type" : "object",
+    "properties" : {
+        "declaredAsBaseType" : {
+            "$ref" : "#/$defs/BaseType"
+        }
+    }
+}