org.apache.tajo.json.CommonGsonHelper.java Source code

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Here is the source code for org.apache.tajo.json.CommonGsonHelper.java

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/**
 * 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 org.apache.tajo.util.TUtil;

import java.lang.reflect.Type;
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 = TUtil.newHashMap();
        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 + "'");
    }
}