tajo-common/src/main/java/org/apache/tajo/json/CommonGsonHelper.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.tajo.json;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.google.gson.JsonNull;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import org.apache.tajo.datum.Datum;

import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;

public class CommonGsonHelper {
  private static Gson gson;
  private static Gson gsonPretty;

  private CommonGsonHelper() {
  }

	private static Map<Type, GsonSerDerAdapter<?>> registerAdapters() {
    Map<Type, GsonSerDerAdapter<?>> adapters = new HashMap<>();
    adapters.put(Datum.class, new DatumAdapter());

    return adapters;
	}

	public static Gson getInstance() {
	  if (gson == null ) {
      GsonHelper helper = new GsonHelper(registerAdapters());
      gson = helper.getGson();
	  }
	  return gson;
	}

  public static Gson getPrettyInstance() {
    if (gsonPretty == null) {
      GsonBuilder prettyBuilder = new GsonBuilder()
          .setPrettyPrinting()
          .excludeFieldsWithoutExposeAnnotation();
      GsonHelper.registerAdapters(prettyBuilder, registerAdapters());
      gsonPretty = prettyBuilder.create();
    }

    return gsonPretty;
  }

  public static String toJson(GsonObject object, Class<? extends GsonObject> clazz) {
    return getInstance().toJson(object, clazz);
  }

  public static <T extends GsonObject> T fromJson(String json, Class<T> clazz) {
    return getInstance().fromJson(json, clazz);
  }

  /**
   * A helper method that gets a JSON object member value after making sure it exists and has a valid value. Useful when
   * a member value should present to proceed.
   * @param object A JSON object to get a member value from
   * @param memberName The name of a member to get value of
   * @return {@link JsonElement} value read from the given member
   * @throws JsonParseException When the specified member does not exist or have a value.
   */
  public static JsonElement getOrDie(JsonObject object, String memberName) throws JsonParseException {
    if (object.has(memberName)) {
      JsonElement element = object.get(memberName);
      if (!JsonNull.INSTANCE.equals(element)) {
        return element;
      }
    }
    throw new JsonParseException("Field '" + memberName + "' not found in JSON object '" + object + "'");
  }
}