fix: return class that implement both JsonNode and JsonValue

src/main/java/com/flowingcode/vaadin/jsonmigration/ElementalArrayNode.java

@@ -0,0 +1,53 @@
+/*-
+ * #%L
+ * Json Migration Helper
+ * %%
+ * Copyright (C) 2025 Flowing Code
+ * %%
+ * 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.flowingcode.vaadin.jsonmigration;
+
+import elemental.json.JsonArray;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.node.ArrayNode;
+import tools.jackson.databind.node.JsonNodeFactory;
+
+@SuppressWarnings("serial")
+class ElementalArrayNode extends ArrayNode implements UnsupportedJsonValueImpl {
+
+  public ElementalArrayNode(JsonArray a) {
+    super(JsonNodeFactory.instance, children(a));
+  }
+
+  private static List<JsonNode> children(JsonArray a) {
+    switch (a.length()) {
+      case 0:
+        return Collections.emptyList();
+      case 1:
+        return Collections.singletonList(JsonMigrationHelper25.convertToJsonNode(a.get(0)));
+      default:
+        List<JsonNode> children = new ArrayList<>(a.length());
+        for (int i = 0, n = a.length(); i < n; i++) {
+          children.add(JsonMigrationHelper25.convertToJsonNode(a.get(i)));
+        }
+        return children;
+    }
+  }
+
+}
+

src/main/java/com/flowingcode/vaadin/jsonmigration/ElementalBooleanNode.java

@@ -0,0 +1,38 @@
+/*-
+ * #%L
+ * Json Migration Helper
+ * %%
+ * Copyright (C) 2025 Flowing Code
+ * %%
+ * 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.flowingcode.vaadin.jsonmigration;
+
+import tools.jackson.databind.node.BooleanNode;
+
+@SuppressWarnings("serial")
+class ElementalBooleanNode extends BooleanNode implements UnsupportedJsonValueImpl {
+
+  public ElementalBooleanNode(boolean value) {
+    super(value);
+  }
+
+}
+
+
+
+
+
+
+

src/main/java/com/flowingcode/vaadin/jsonmigration/ElementalNullNode.java

@@ -0,0 +1,32 @@
+/*-
+ * #%L
+ * Json Migration Helper
+ * %%
+ * Copyright (C) 2025 Flowing Code
+ * %%
+ * 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.flowingcode.vaadin.jsonmigration;
+
+import tools.jackson.databind.node.NullNode;
+
+@SuppressWarnings("serial")
+class ElementalNullNode extends NullNode implements UnsupportedJsonValueImpl {
+
+  public ElementalNullNode() {
+    super();
+  }
+
+}
+

src/main/java/com/flowingcode/vaadin/jsonmigration/ElementalNumberNode.java

@@ -0,0 +1,32 @@
+/*-
+ * #%L
+ * Json Migration Helper
+ * %%
+ * Copyright (C) 2025 Flowing Code
+ * %%
+ * 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.flowingcode.vaadin.jsonmigration;
+
+import tools.jackson.databind.node.DoubleNode;
+
+@SuppressWarnings("serial")
+class ElementalNumberNode extends DoubleNode implements UnsupportedJsonValueImpl {
+
+  public ElementalNumberNode(double value) {
+    super(value);
+  }
+
+}
+

src/main/java/com/flowingcode/vaadin/jsonmigration/ElementalObjectNode.java

@@ -0,0 +1,56 @@
+/*-
+ * #%L
+ * Json Migration Helper
+ * %%
+ * Copyright (C) 2025 Flowing Code
+ * %%
+ * 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.flowingcode.vaadin.jsonmigration;
+
+import static com.flowingcode.vaadin.jsonmigration.JsonMigrationHelper25.convertToJsonNode;
+import elemental.json.JsonObject;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.node.JsonNodeFactory;
+import tools.jackson.databind.node.ObjectNode;
+
+@SuppressWarnings("serial")
+class ElementalObjectNode extends ObjectNode implements UnsupportedJsonValueImpl {
+
+  public ElementalObjectNode(JsonObject o) {
+    super(JsonNodeFactory.instance, children(o));
+  }
+
+  private static Map<String, JsonNode> children(JsonObject o) {
+    String keys[] = o.keys();
+    switch (keys.length) {
+      case 0:
+        return Collections.emptyMap();
+      case 1:
+        return Collections.singletonMap(keys[0], convertToJsonNode(o.get(keys[0])));
+      default:
+        Map<String, JsonNode> children = new LinkedHashMap<>(keys.length);
+        for (String key : keys) {
+          children.put(key, convertToJsonNode(o.get(key)));
+        }
+        return children;
+    }
+  }
+
+}
+
+

src/main/java/com/flowingcode/vaadin/jsonmigration/ElementalStringNode.java

@@ -0,0 +1,31 @@
+/*-
+ * #%L
+ * Json Migration Helper
+ * %%
+ * Copyright (C) 2025 Flowing Code
+ * %%
+ * 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.flowingcode.vaadin.jsonmigration;
+
+import tools.jackson.databind.node.StringNode;
+
+@SuppressWarnings("serial")
+class ElementalStringNode extends StringNode implements UnsupportedJsonValueImpl {
+
+  public ElementalStringNode(String value) {
+    super(value);
+  }
+
+}

src/main/java/com/flowingcode/vaadin/jsonmigration/JsonMigration.java

@@ -72,7 +72,7 @@ private static Class<?> lookup_BaseJsonNode() {
    * @param object the object to convert
    * @return an {@code Object} suitable to use as the result of a {@code ClientCallable} method.
    */
-  public static Object convertToClientCallableResult(Object object) {
+  public static <T extends JsonValue> T convertToClientCallableResult(T object) {
     return helper.convertToClientCallableResult(object);
   }
 

src/main/java/com/flowingcode/vaadin/jsonmigration/JsonMigrationHelper.java

@@ -29,7 +29,7 @@ interface JsonMigrationHelper {
 
   JsonValue convertToJsonValue(Object object);
 
-  Object convertToClientCallableResult(Object object);
+  <T extends JsonValue> T convertToClientCallableResult(T object);
 
   Object invoke(Method method, Object instance, Object... args);
 

src/main/java/com/flowingcode/vaadin/jsonmigration/JsonMigrationHelper25.java

@@ -55,12 +55,28 @@ public JsonValue convertToJsonValue(Object object) {
     }
   } 
 
+  @SuppressWarnings("unchecked")
   @Override
-  public Object convertToClientCallableResult(Object object) {
-    if (object instanceof JsonValue) {
-      return convertToJsonNode((JsonValue) object);
+  public JsonValue convertToClientCallableResult(JsonValue object) {
+    if (object == null) {
+      return null;
     } else {
-      return object;
+      switch (object.getType()) {
+        case OBJECT:
+          return new ElementalObjectNode((JsonObject) object);
+        case ARRAY:
+          return new ElementalArrayNode((JsonArray) object);
+        case BOOLEAN:
+          return new ElementalBooleanNode(object.asBoolean());
+        case NULL:
+          return new ElementalNullNode();
+        case NUMBER:
+          return new ElementalNumberNode(object.asNumber());
+        case STRING:
+          return new ElementalStringNode(object.asString());
+        default:
+          throw new IllegalArgumentException();
+      }
     }
   }
 
@@ -155,7 +171,7 @@ private static JsonValue convertToJsonValue(JsonNode jsonNode) {
 
   private static final JsonNodeFactory nodeFactory = JsonNodeFactory.instance;
 
-  private static BaseJsonNode convertToJsonNode(JsonValue jsonValue) {
+  static BaseJsonNode convertToJsonNode(JsonValue jsonValue) {
     switch (jsonValue.getType()) {
       case OBJECT:
         JsonObject jsonObject = (JsonObject) jsonValue;

src/main/java/com/flowingcode/vaadin/jsonmigration/LegacyJsonMigrationHelper.java

@@ -41,7 +41,7 @@ public JsonValue convertToJsonValue(Object object) {
   }
 
   @Override
-  public Object convertToClientCallableResult(Object object) {
+  public <T extends JsonValue> T convertToClientCallableResult(T object) {
     return object;
   }
 

src/main/java/com/flowingcode/vaadin/jsonmigration/UnsupportedJsonValueImpl.java

@@ -0,0 +1,62 @@
+/*-
+ * #%L
+ * Json Migration Helper
+ * %%
+ * Copyright (C) 2025 Flowing Code
+ * %%
+ * 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.flowingcode.vaadin.jsonmigration;
+
+import elemental.json.JsonType;
+import elemental.json.JsonValue;
+
+interface UnsupportedJsonValueImpl extends JsonValue {
+
+  @Override
+  default boolean asBoolean() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  default double asNumber() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  default String asString() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  default JsonType getType() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  default String toJson() {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  default boolean jsEquals(JsonValue value) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  default Object toNative() {
+    throw new UnsupportedOperationException();
+  }
+
+}