Testing Runtime Type Adapter Wrapper Implementation in Google Gson

google/gson

gson/src/test/java/com/google/gson/functional/TypeAdapterRuntimeTypeWrapperTest.java

            
/*
 * Copyright (C) 2022 Google Inc.
 *
 * 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.google.gson.functional;

import static com.google.common.truth.Truth.assertThat;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializer;
import com.google.gson.TypeAdapter;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
import java.lang.reflect.Type;
import org.junit.Test;

public class TypeAdapterRuntimeTypeWrapperTest {
  private static class Base {}

  private static class Subclass extends Base {
    @SuppressWarnings("unused")
    String f = "test";
  }

  private static class Container {
    @SuppressWarnings("unused")
    Base b = new Subclass();
  }

  private static class Deserializer implements JsonDeserializer<Base> {
    @Override
    public Base deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) {
      throw new AssertionError("not needed for this test");
    }
  }

  /**
   * When custom {@link JsonSerializer} is registered for Base should prefer that over reflective
   * adapter for Subclass for serialization.
   */
  @Test
  public void testJsonSerializer() {
    Gson gson =
        new GsonBuilder()
            .registerTypeAdapter(
                Base.class,
                (JsonSerializer<Base>) (src, typeOfSrc, context) -> new JsonPrimitive("serializer"))
            .create();

    String json = gson.toJson(new Container());
    assertThat(json).isEqualTo("{\"b\":\"serializer\"}");
  }

  /**
   * When only {@link JsonDeserializer} is registered for Base, then on serialization should prefer
   * reflective adapter for Subclass since Base would use reflective adapter as delegate.
   */
  @Test
  public void testJsonDeserializer_ReflectiveSerializerDelegate() {
    Gson gson = new GsonBuilder().registerTypeAdapter(Base.class, new Deserializer()).create();

    String json = gson.toJson(new Container());
    assertThat(json).isEqualTo("{\"b\":{\"f\":\"test\"}}");
  }

  /**
   * When {@link JsonDeserializer} with custom adapter as delegate is registered for Base, then on
   * serialization should prefer custom adapter delegate for Base over reflective adapter for
   * Subclass.
   */
  @Test
  public void testJsonDeserializer_CustomSerializerDelegate() {
    Gson gson =
        new GsonBuilder()
            // Register custom delegate
            .registerTypeAdapter(
                Base.class,
                new TypeAdapter<Base>() {
                  @Override
                  public Base read(JsonReader in) throws IOException {
                    throw new UnsupportedOperationException();
                  }

                  @Override
                  public void write(JsonWriter out, Base value) throws IOException {
                    out.value("custom delegate");
                  }
                })
            .registerTypeAdapter(Base.class, new Deserializer())
            .create();

    String json = gson.toJson(new Container());
    assertThat(json).isEqualTo("{\"b\":\"custom delegate\"}");
  }

  /**
   * When two (or more) {@link JsonDeserializer}s are registered for Base which eventually fall back
   * to reflective adapter as delegate, then on serialization should prefer reflective adapter for
   * Subclass.
   */
  @Test
  public void testJsonDeserializer_ReflectiveTreeSerializerDelegate() {
    Gson gson =
        new GsonBuilder()
            // Register delegate which itself falls back to reflective serialization
            .registerTypeAdapter(Base.class, new Deserializer())
            .registerTypeAdapter(Base.class, new Deserializer())
            .create();

    String json = gson.toJson(new Container());
    assertThat(json).isEqualTo("{\"b\":{\"f\":\"test\"}}");
  }

  /**
   * When {@link JsonDeserializer} with {@link JsonSerializer} as delegate is registered for Base,
   * then on serialization should prefer {@code JsonSerializer} over reflective adapter for
   * Subclass.
   */
  @Test
  public void testJsonDeserializer_JsonSerializerDelegate() {
    Gson gson =
        new GsonBuilder()
            // Register JsonSerializer as delegate
            .registerTypeAdapter(
                Base.class,
                (JsonSerializer<Base>)
                    (src, typeOfSrc, context) -> new JsonPrimitive("custom delegate"))
            .registerTypeAdapter(Base.class, new Deserializer())
            .create();

    String json = gson.toJson(new Container());
    assertThat(json).isEqualTo("{\"b\":\"custom delegate\"}");
  }

  /**
   * When a {@link JsonDeserializer} is registered for Subclass, and a custom {@link JsonSerializer}
   * is registered for Base, then Gson should prefer the reflective adapter for Subclass for
   * backward compatibility (see https://github.com/google/gson/pull/1787#issuecomment-1222175189)
   * even though normally TypeAdapterRuntimeTypeWrapper should prefer the custom serializer for
   * Base.
   */
  @Test
  public void testJsonDeserializer_SubclassBackwardCompatibility() {
    Gson gson =
        new GsonBuilder()
            .registerTypeAdapter(
                Subclass.class,
                (JsonDeserializer<Subclass>)
                    (json, typeOfT, context) -> {
                      throw new AssertionError("not needed for this test");
                    })
            .registerTypeAdapter(
                Base.class,
                (JsonSerializer<Base>) (src, typeOfSrc, context) -> new JsonPrimitive("base"))
            .create();

    String json = gson.toJson(new Container());
    assertThat(json).isEqualTo("{\"b\":{\"f\":\"test\"}}");
  }

  private static class CyclicBase {
    @SuppressWarnings("unused")
    CyclicBase f;
  }

  private static class CyclicSub extends CyclicBase {
    @SuppressWarnings("unused")
    int i;

    public CyclicSub(int i) {
      this.i = i;
    }
  }

  /**
   * Tests behavior when the type of a field refers to a type whose adapter is currently in the
   * process of being created. For these cases {@link Gson} uses a future adapter for the type. That
   * adapter later uses the actual adapter as delegate.
   */
  @Test
  public void testGsonFutureAdapter() {
    CyclicBase b = new CyclicBase();
    b.f = new CyclicSub(2);
    String json = new Gson().toJson(b);
    assertThat(json).isEqualTo("{\"f\":{\"i\":2}}");
  }
}