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    • com.github.wnameless.json.flattener.JsonFlattener Maven / Gradle / Ivy

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    A Java utility used to flatten nested JSON objects and even more to unflatten it back

    There is a newer version: 0.7.1
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    /*
 * 
 * Copyright 2015 Wei-Ming Wu
 *
 * 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.github.wnameless.json.flattener;

import static com.github.wnameless.json.flattener.FlattenMode.MONGODB;
import static com.github.wnameless.json.flattener.IndexedPeekIterator.newIndexedPeekIterator;
import static java.util.Collections.emptyMap;
import static org.apache.commons.lang3.Validate.isTrue;
import static org.apache.commons.lang3.Validate.notNull;

import java.io.IOException;
import java.io.Reader;
import java.math.BigDecimal;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Map;
import java.util.regex.Pattern;

import org.apache.commons.lang3.StringUtils;

import com.eclipsesource.json.Json;
import com.eclipsesource.json.JsonObject.Member;
import com.eclipsesource.json.JsonValue;

/**
 * 
 * {@link JsonFlattener} flattens any JSON nested objects or arrays into a
 * flattened JSON string or a Map{@literal }. The String key
 * will represents the corresponding position of value in the original nested
 * objects or arrays and the Object value are either String, Boolean, Long,
 * Double or null. 
    
 * 
    
 * For example:
    
 * A nested JSON
    
 * { "a" : { "b" : 1, "c": null, "d": [false, true] }, "e": "f", "g":2.3 }
    
 * 
    
 * can be turned into a flattened JSON 
    
 * { "a.b": 1, "a.c": null, "a.d[0]": false, "a.d[1]": true, "e": "f", "g":2.3 }
 * 
    
 * 
    
 * or into a Map
    
 * {
    
 *   a.b=1,
    
 *   a.c=null,
    
 *   a.d[0]=false,
    
 *   a.d[1]=true,
    
 *   e=f,
    
 *   g=2.3
    
 * }
 *
 * @author Wei-Ming Wu
 *
 */
public final class JsonFlattener {

  /**
   * {@link ROOT} is the default key of the Map returned by
   * {@link #flattenAsMap}. When {@link JsonFlattener} processes a JSON string
   * which is not a JSON object or array, the final outcome may not suit in a
   * Java Map. At that moment, {@link JsonFlattener} will put the result in the
   * Map with {@link ROOT} as its key.
   */
  public static final String ROOT = "root";

  /**
   * Returns a flattened JSON string.
   * 
   * @param json
   *          the JSON string
   * @return a flattened JSON string.
   */
  public static String flatten(String json) {
    return new JsonFlattener(json).flatten();
  }

  /**
   * Returns a flattened JSON as Map.
   * 
   * @param json
   *          the JSON string
   * @return a flattened JSON as Map
   */
  public static Map flattenAsMap(String json) {
    return new JsonFlattener(json).flattenAsMap();
  }

  private final JsonValue source;

  private JsonifyLinkedHashMap flattenedMap;
  private final Deque> elementIters =
      new ArrayDeque>();

  private FlattenMode flattenMode = FlattenMode.NORMAL;
  private StringEscapePolicy policy = StringEscapePolicy.NORMAL;
  private Character separator = '.';
  private Character leftBracket = '[';
  private Character rightBracket = ']';
  private PrintMode printMode = PrintMode.MINIMAL;
  private KeyTransformer keyTrans = null;

  /**
   * Creates a JSON flattener.
   * 
   * @param json
   *          the JSON string
   */
  public JsonFlattener(String json) {
    source = Json.parse(json);
  }

  /**
   * Creates a JSON flattener.
   * 
   * @param jsonReader
   *          the JSON reader
   * @throws IOException
   *           if jsonReader cannot be read
   */
  public JsonFlattener(Reader jsonReader) throws IOException {
    source = Json.parse(jsonReader);
  }

  /**
   * A fluent setter to setup a mode of the {@link JsonFlattener}.
   * 
   * @param flattenMode
   *          a {@link FlattenMode}
   * @return this {@link JsonFlattener}
   */
  public JsonFlattener withFlattenMode(FlattenMode flattenMode) {
    this.flattenMode = notNull(flattenMode);
    flattenedMap = null;
    return this;
  }

  /**
   * A fluent setter to setup the JSON string escape policy.
   * 
   * @param policy
   *          a {@link StringEscapePolicy}
   * @return this {@link JsonFlattener}
   */
  public JsonFlattener withStringEscapePolicy(StringEscapePolicy policy) {
    this.policy = notNull(policy);
    flattenedMap = null;
    return this;
  }

  /**
   * A fluent setter to setup the separator within a key in the flattened JSON.
   * The default separator is a dot(.).
   * 
   * @param separator
   *          any character
   * @return this {@link JsonFlattener}
   */
  public JsonFlattener withSeparator(char separator) {
    isTrue(!Character.toString(separator).matches("[\"\\s]"),
        "Separator contains illegal chracter(%s)",
        Character.toString(separator));
    isTrue(!leftBracket.equals(separator) && !rightBracket.equals(separator),
        "Separator(%s) is already used in brackets",
        Character.toString(separator));

    this.separator = separator;
    flattenedMap = null;
    return this;
  }

  private String illegalBracketsRegex() {
    return "[\"\\s" + Pattern.quote(this.separator.toString()) + "]";
  }

  /**
   * A fluent setter to setup the left and right brackets within a key in the
   * flattened JSON. The default left and right brackets are left square
   * bracket([) and right square bracket(]).
   * 
   * @param leftBracket
   *          any character
   * @param rightBracket
   *          any character
   * @return this {@link JsonFlattener}
   */
  public JsonFlattener withLeftAndRightBrackets(char leftBracket,
      char rightBracket) {
    isTrue(leftBracket != rightBracket, "Both brackets cannot be the same");
    isTrue(!Character.toString(leftBracket).matches(illegalBracketsRegex()),
        "Left bracket contains illegal chracter(%s)",
        Character.toString(leftBracket));
    isTrue(!Character.toString(rightBracket).matches(illegalBracketsRegex()),
        "Right bracket contains illegal chracter(%s)",
        Character.toString(rightBracket));

    this.leftBracket = leftBracket;
    this.rightBracket = rightBracket;
    flattenedMap = null;
    return this;
  }

  /**
   * A fluent setter to setup a print mode of the {@link JsonFlattener}. The
   * default print mode is minimal.
   * 
   * @param printMode
   *          a {@link PrintMode}
   * @return this {@link JsonFlattener}
   */
  public JsonFlattener withPrintMode(PrintMode printMode) {
    this.printMode = notNull(printMode);
    return this;
  }

  /**
   * A fluent setter to setup a {@link KeyTransformer} of the
   * {@link JsonFlattener}.
   * 
   * @param keyTrans
   *          a {@link KeyTransformer}
   * @return this {@link JsonFlattener}
   */
  public JsonFlattener withKeyTransformer(KeyTransformer keyTrans) {
    this.keyTrans = notNull(keyTrans);
    flattenedMap = null;
    return this;
  }

  /**
   * Returns a flattened JSON string.
   * 
   * @return a flattened JSON string
   */
  public String flatten() {
    flattenAsMap();

    if (source.isObject() || isObjectifiableArray())
      return flattenedMap.toString(printMode);
    else
      return javaObj2Json(flattenedMap.get(ROOT));
  }

  private boolean isObjectifiableArray() {
    return source.isArray() && !flattenedMap.containsKey(ROOT);
  }

  private String javaObj2Json(Object obj) {
    if (obj == null) {
      return "null";
    } else if (obj instanceof CharSequence) {
      StringBuilder sb = new StringBuilder();
      sb.append('"');
      sb.append(
          policy.getCharSequenceTranslator().translate((CharSequence) obj));
      sb.append('"');
      return sb.toString();
    } else if (obj instanceof JsonifyArrayList) {
      JsonifyArrayList list = (JsonifyArrayList) obj;
      return list.toString(printMode);
    } else {
      return obj.toString();
    }
  }

  /**
   * Returns a flattened JSON as Map.
   * 
   * @return a flattened JSON as Map
   */
  public Map flattenAsMap() {
    if (flattenedMap != null) return flattenedMap;

    flattenedMap = newJsonifyLinkedHashMap();
    reduce(source);

    while (!elementIters.isEmpty()) {
      IndexedPeekIterator deepestIter = elementIters.getLast();
      if (!deepestIter.hasNext()) {
        elementIters.removeLast();
      } else if (deepestIter.peek() instanceof Member) {
        Member mem = (Member) deepestIter.next();
        reduce(mem.getValue());
      } else { // JsonValue
        JsonValue val = (JsonValue) deepestIter.next();
        reduce(val);
      }
    }

    return flattenedMap;
  }

  private void reduce(JsonValue val) {
    if (val.isObject() && val.asObject().iterator().hasNext()) {
      elementIters.add(newIndexedPeekIterator(val.asObject()));
    } else if (val.isArray() && val.asArray().iterator().hasNext()) {
      switch (flattenMode) {
        case KEEP_ARRAYS:
          JsonifyArrayList array = newJsonifyArrayList();
          for (JsonValue value : val.asArray()) {
            array.add(jsonVal2Obj(value));
          }
          flattenedMap.put(computeKey(), array);
          break;
        default:
          elementIters.add(newIndexedPeekIterator(val.asArray()));
      }
    } else {
      String key = computeKey();
      Object value = jsonVal2Obj(val);
      // Check NOT empty JSON object
      if (!(ROOT.equals(key) && emptyMap().equals(value)))
        flattenedMap.put(key, jsonVal2Obj(val));
    }
  }

  private Object jsonVal2Obj(JsonValue val) {
    if (val.isBoolean()) return val.asBoolean();
    if (val.isString()) return val.asString();
    if (val.isNumber()) return new BigDecimal(val.toString());
    switch (flattenMode) {
      case KEEP_ARRAYS:
        if (val.isArray()) {
          JsonifyArrayList array = newJsonifyArrayList();
          for (JsonValue value : val.asArray()) {
            array.add(jsonVal2Obj(value));
          }
          return array;
        } else if (val.isObject()) {
          if (val.asObject().iterator().hasNext()) {
            return newJsonFlattener(val.toString()).flattenAsMap();
          } else {
            return newJsonifyLinkedHashMap();
          }
        }
      default:
        if (val.isArray()) {
          return newJsonifyArrayList();
        } else if (val.isObject()) {
          return newJsonifyLinkedHashMap();
        }
    }

    return null;
  }

  private boolean hasReservedCharacters(String key) {
    if (flattenMode.equals(MONGODB) && StringUtils.containsAny(key, separator))
      throw new IllegalArgumentException("Key cannot contain separator("
          + separator + ") in FlattenMode." + MONGODB);

    return StringUtils.containsAny(key, separator, leftBracket, rightBracket);
  }

  private String computeKey() {
    if (elementIters.isEmpty()) return ROOT;

    StringBuilder sb = new StringBuilder();

    for (IndexedPeekIterator iter : elementIters) {
      if (iter.getCurrent() instanceof Member) {
        String key = ((Member) iter.getCurrent()).getName();
        if (keyTrans != null) key = keyTrans.transform(key);
        if (hasReservedCharacters(key)) {
          sb.append(leftBracket);
          sb.append('\\');
          sb.append('"');
          sb.append(policy.getCharSequenceTranslator().translate(key));
          sb.append('\\');
          sb.append('"');
          sb.append(rightBracket);
        } else {
          if (sb.length() != 0) sb.append(separator);
          sb.append(policy.getCharSequenceTranslator().translate(key));
        }
      } else { // JsonValue
        sb.append(flattenMode.equals(MONGODB) ? separator : leftBracket);
        sb.append(iter.getIndex());
        sb.append(flattenMode.equals(MONGODB) ? "" : rightBracket);
      }
    }

    return sb.toString();
  }

  private  JsonifyArrayList newJsonifyArrayList() {
    JsonifyArrayList array = new JsonifyArrayList();
    array.setTranslator(policy.getCharSequenceTranslator());
    return array;
  }

  private  JsonifyLinkedHashMap newJsonifyLinkedHashMap() {
    JsonifyLinkedHashMap map = new JsonifyLinkedHashMap();
    map.setTranslator(policy.getCharSequenceTranslator());
    return map;
  }

  private JsonFlattener newJsonFlattener(String json) {
    return new JsonFlattener(json).withFlattenMode(flattenMode)
        .withSeparator(separator).withStringEscapePolicy(policy)
        .withPrintMode(printMode);
  }

  @Override
  public int hashCode() {
    int result = 27;
    result = 31 * result + source.hashCode();
    return result;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof JsonFlattener)) return false;
    return source.equals(((JsonFlattener) o).source);
  }

  @Override
  public String toString() {
    return "JsonFlattener{source=" + source + "}";
  }

}
    
    
    
    

    




    
    
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