Merge pull request #12 from linked-planet/feature/gson

add GsonUtil that provides a GsonBuilder compatible with the model, otherwise every consumer has to solve the sealed class mapping themselves

Author: HighKo

kotlin-insight-client/kotlin-insight-client-api/pom.xml

@@ -28,5 +28,11 @@
             <version>2.0.1.Final</version>
             <scope>provided</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>2.2.2-atlassian-1</version>
+            <scope>provided</scope>
+        </dependency>
     </dependencies>
 </project>

kotlin-insight-client/kotlin-insight-client-api/src/main/kotlin/com/linkedplanet/kotlininsightclient/api/impl/GsonUtil.kt

@@ -0,0 +1,52 @@
+/*-
+ * #%L
+ * kotlin-insight-client-api
+ * %%
+ * Copyright (C) 2022 - 2023 linked-planet GmbH
+ * %%
+ * 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.
+ * #L%
+ */
+package com.linkedplanet.kotlininsightclient.api.impl
+
+import com.google.gson.GsonBuilder
+import com.google.gson.TypeAdapter
+import com.google.gson.stream.JsonReader
+import com.google.gson.stream.JsonWriter
+import com.linkedplanet.kotlininsightclient.api.model.InsightAttribute
+import com.linkedplanet.kotlininsightclient.api.model.ObjectTypeSchemaAttribute
+import java.time.ZonedDateTime
+
+
+class GsonUtil {
+    companion object {
+        fun gsonBuilder(): GsonBuilder = GsonBuilder()
+            .registerTypeAdapter(ZonedDateTime::class.java, zonedDateTimeAdapter)
+            .registerTypeAdapterFactory(SealedTypeAdapterFactory.of(InsightAttribute::class))
+            .registerTypeAdapterFactory(SealedTypeAdapterFactory.of(ObjectTypeSchemaAttribute::class,
+                typeFieldName = "type",
+                jsonNameForType = { it.simpleName!!.removeSuffix("Schema") to it }
+            ))
+
+
+        private val zonedDateTimeAdapter = object : TypeAdapter<ZonedDateTime>() {
+            override fun write(out: JsonWriter, value: ZonedDateTime?) {
+                out.value(value.toString())
+            }
+
+            override fun read(`in`: JsonReader): ZonedDateTime {
+                return ZonedDateTime.parse(`in`.nextString())
+            }
+        }
+    }
+}

kotlin-insight-client/kotlin-insight-client-api/src/main/kotlin/com/linkedplanet/kotlininsightclient/api/impl/SealedTypeAdapterFactory.kt

@@ -0,0 +1,102 @@
+/*-
+ * #%L
+ * kotlin-insight-client-api
+ * %%
+ * Copyright (C) 2022 - 2023 linked-planet GmbH
+ * %%
+ * 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.
+ * #L%
+ */
+package com.linkedplanet.kotlininsightclient.api.impl
+
+import com.google.gson.Gson
+import com.google.gson.JsonElement
+import com.google.gson.JsonObject
+import com.google.gson.JsonParseException
+import com.google.gson.JsonPrimitive
+import com.google.gson.TypeAdapter
+import com.google.gson.TypeAdapterFactory
+import com.google.gson.reflect.TypeToken
+import com.google.gson.stream.JsonReader
+import com.google.gson.stream.JsonWriter
+import kotlin.reflect.KClass
+
+/**
+ * Creates TypeAdaptors for sealed classes.
+ * Especially for deserialization Gson needs to know which class to instantiate.
+ *
+ * @param baseType The parent sealed class
+ * @param typeFieldName the additional field inside the json that contains the name of the type
+ * @param jsonNameForType Choose a different name for the type einside the json, other than the name of the class itself (defaults to simplename)
+ */
+class SealedTypeAdapterFactory<T : Any> private constructor(
+    private val baseType: KClass<T>,
+    private val typeFieldName: String,
+    jsonNameForType: (KClass<out T>) -> Pair<String, KClass<out T>>
+) : TypeAdapterFactory {
+
+    private val subclasses = baseType.sealedSubclasses
+    private val nameToSubclass: Map<String, KClass<out T>> = subclasses.associate(jsonNameForType)
+
+    init {
+        if (!baseType.isSealed) throw IllegalArgumentException("$baseType is not a sealed class")
+    }
+
+    override fun <R : Any> create(gson: Gson, type: TypeToken<R>?): TypeAdapter<R>? {
+        if (type == null || subclasses.isEmpty() || subclasses.none { type.rawType.isAssignableFrom(it.java) }) return null
+        val elementTypeAdapter = gson.getAdapter(JsonElement::class.java)
+        val subclassToDelegate: Map<KClass<*>, TypeAdapter<*>> = subclasses.associateWith {
+            gson.getDelegateAdapter(this, TypeToken.get(it.java))
+        }
+
+        return object : TypeAdapter<R>() {
+
+            override fun write(writer: JsonWriter, value: R) {
+                val srcType = value::class
+                val label = srcType.simpleName!!
+
+                @Suppress("UNCHECKED_CAST") val delegate = subclassToDelegate[srcType] as TypeAdapter<R>
+                val jsonObject = delegate.toJsonTree(value).asJsonObject
+
+                val clone = JsonObject()
+                if (!jsonObject.has(typeFieldName)) {
+                    clone.add(typeFieldName, JsonPrimitive(label))
+                }
+                jsonObject.entrySet().forEach {
+                    clone.add(it.key, it.value)
+                }
+                elementTypeAdapter.write(writer, clone)
+            }
+
+            override fun read(reader: JsonReader): R {
+                val element = elementTypeAdapter.read(reader)
+                val labelElement = element.asJsonObject.remove(typeFieldName) ?: throw JsonParseException(
+                    "cannot deserialize $baseType because it does not define a field named $typeFieldName"
+                )
+                val name = labelElement.asString
+                val subclass = nameToSubclass[name] ?: throw JsonParseException("cannot find $name subclass of $baseType")
+                @Suppress("UNCHECKED_CAST")
+                return (subclass.objectInstance as? R) ?: (subclassToDelegate[subclass]!!.fromJsonTree(element) as R)
+            }
+
+        }
+    }
+
+    companion object {
+        fun <T : Any> of(
+            clz: KClass<T>,
+            typeFieldName: String = "type",
+            jsonNameForType: (KClass<out T>) -> Pair<String, KClass<out T>> = { it.simpleName!! to it }
+        ) = SealedTypeAdapterFactory(clz, typeFieldName, jsonNameForType)
+    }
+}