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Java example source code file (TreeTypeAdapter.java)

This example Java source code file (TreeTypeAdapter.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

class, gson, gsoncontextimpl, ioexception, jsondeserializer, jsonelement, jsonserializer, object, override, reflection, singletypefactory, suppresswarnings, treetypeadapter, typeadapterfactory, typetoken

The TreeTypeAdapter.java Java example source code

/*
 * Copyright (C) 2011 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.internal.bind;

import com.google.gson.Gson;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.internal.$Gson$Preconditions;
import com.google.gson.internal.Streams;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
import java.lang.reflect.Type;

/**
 * Adapts a Gson 1.x tree-style adapter as a streaming TypeAdapter. Since the
 * tree adapter may be serialization-only or deserialization-only, this class
 * has a facility to lookup a delegate type adapter on demand.
 */
public final class TreeTypeAdapter<T> extends TypeAdapter {
  private final JsonSerializer<T> serializer;
  private final JsonDeserializer<T> deserializer;
  private final Gson gson;
  private final TypeToken<T> typeToken;
  private final TypeAdapterFactory skipPast;
  private final GsonContextImpl context = new GsonContextImpl();

  /** The delegate is lazily created because it may not be needed, and creating it may fail. */
  private TypeAdapter<T> delegate;

  public TreeTypeAdapter(JsonSerializer<T> serializer, JsonDeserializer deserializer,
      Gson gson, TypeToken<T> typeToken, TypeAdapterFactory skipPast) {
    this.serializer = serializer;
    this.deserializer = deserializer;
    this.gson = gson;
    this.typeToken = typeToken;
    this.skipPast = skipPast;
  }

  @Override public T read(JsonReader in) throws IOException {
    if (deserializer == null) {
      return delegate().read(in);
    }
    JsonElement value = Streams.parse(in);
    if (value.isJsonNull()) {
      return null;
    }
    return deserializer.deserialize(value, typeToken.getType(), context);
  }

  @Override public void write(JsonWriter out, T value) throws IOException {
    if (serializer == null) {
      delegate().write(out, value);
      return;
    }
    if (value == null) {
      out.nullValue();
      return;
    }
    JsonElement tree = serializer.serialize(value, typeToken.getType(), context);
    Streams.write(tree, out);
  }

  private TypeAdapter<T> delegate() {
    TypeAdapter<T> d = delegate;
    return d != null
        ? d
        : (delegate = gson.getDelegateAdapter(skipPast, typeToken));
  }

  /**
   * Returns a new factory that will match each type against {@code exactType}.
   */
  public static TypeAdapterFactory newFactory(TypeToken<?> exactType, Object typeAdapter) {
    return new SingleTypeFactory(typeAdapter, exactType, false, null);
  }

  /**
   * Returns a new factory that will match each type and its raw type against
   * {@code exactType}.
   */
  public static TypeAdapterFactory newFactoryWithMatchRawType(
      TypeToken<?> exactType, Object typeAdapter) {
    // only bother matching raw types if exact type is a raw type
    boolean matchRawType = exactType.getType() == exactType.getRawType();
    return new SingleTypeFactory(typeAdapter, exactType, matchRawType, null);
  }

  /**
   * Returns a new factory that will match each type's raw type for assignability
   * to {@code hierarchyType}.
   */
  public static TypeAdapterFactory newTypeHierarchyFactory(
      Class<?> hierarchyType, Object typeAdapter) {
    return new SingleTypeFactory(typeAdapter, null, false, hierarchyType);
  }

  private static final class SingleTypeFactory implements TypeAdapterFactory {
    private final TypeToken<?> exactType;
    private final boolean matchRawType;
    private final Class<?> hierarchyType;
    private final JsonSerializer<?> serializer;
    private final JsonDeserializer<?> deserializer;

    SingleTypeFactory(Object typeAdapter, TypeToken<?> exactType, boolean matchRawType,
        Class<?> hierarchyType) {
      serializer = typeAdapter instanceof JsonSerializer
          ? (JsonSerializer<?>) typeAdapter
          : null;
      deserializer = typeAdapter instanceof JsonDeserializer
          ? (JsonDeserializer<?>) typeAdapter
          : null;
      $Gson$Preconditions.checkArgument(serializer != null || deserializer != null);
      this.exactType = exactType;
      this.matchRawType = matchRawType;
      this.hierarchyType = hierarchyType;
    }

    @SuppressWarnings("unchecked") // guarded by typeToken.equals() call
    @Override
    public <T> TypeAdapter create(Gson gson, TypeToken type) {
      boolean matches = exactType != null
          ? exactType.equals(type) || matchRawType && exactType.getType() == type.getRawType()
          : hierarchyType.isAssignableFrom(type.getRawType());
      return matches
          ? new TreeTypeAdapter<T>((JsonSerializer) serializer,
              (JsonDeserializer<T>) deserializer, gson, type, this)
          : null;
    }
  }

  private final class GsonContextImpl implements JsonSerializationContext, JsonDeserializationContext {
    @Override public JsonElement serialize(Object src) {
      return gson.toJsonTree(src);
    }
    @Override public JsonElement serialize(Object src, Type typeOfSrc) {
      return gson.toJsonTree(src, typeOfSrc);
    }
    @SuppressWarnings("unchecked")
    @Override public <R> R deserialize(JsonElement json, Type typeOfT) throws JsonParseException {
      return (R) gson.fromJson(json, typeOfT);
    }
  };
}

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