hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/web/utils/JsonUtils.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.hadoop.ozone.web.utils;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectReader;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.fasterxml.jackson.databind.type.CollectionType;

import java.io.IOException;
import java.util.List;

/**
 * JSON Utility functions used in ozone.
 */
public final class JsonUtils {

  // Reuse ObjectMapper instance for improving performance.
  // ObjectMapper is thread safe as long as we always configure instance
  // before use.
  private static final ObjectMapper MAPPER = new ObjectMapper();
  private static final ObjectReader READER = MAPPER.readerFor(Object.class);
  private static final ObjectWriter WRITTER =
      MAPPER.writerWithDefaultPrettyPrinter();

  private JsonUtils() {
    // Never constructed
  }

  public static String toJsonStringWithDefaultPrettyPrinter(String jsonString)
      throws IOException {
    Object json = READER.readValue(jsonString);
    return WRITTER.writeValueAsString(json);
  }

  public static String toJsonString(Object obj) throws IOException {
    return MAPPER.writeValueAsString(obj);
  }

  /**
   * Deserialize a list of elements from a given string,
   * each element in the list is in the given type.
   *
   * @param str json string.
   * @param elementType element type.
   * @return List of elements of type elementType
   * @throws IOException
   */
  public static List<?> toJsonList(String str, Class<?> elementType)
      throws IOException {
    CollectionType type = MAPPER.getTypeFactory()
        .constructCollectionType(List.class, elementType);
    return MAPPER.readValue(str, type);
  }
}