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This library Flattens JSON objects. It can also unflatten JSON objects.
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package be.adaxisoft.flat;
import java.util.Arrays;
import java.util.Iterator;
import java.util.regex.Pattern;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
/**
*
* This library flattens JSON files.
*
* Before:
*
*{
* "key1": {
* "keyA": "valueI"
* },
* "key2": {
* "keyB": "valueII"
* },
* "key3": { "a": { "b": { "c": 2 } } }
*}
*
*
* After:
*
*{
* "key1.keyA": "valueI",
* "key2.keyB": "valueII",
* "key3.a.b.c": 2
*}
*
*
* The library can do the reverse operation as well: unflatten.
*
* @author Gérik Bonaert
*/
public class Flat {
/**
* The default delimiter is used by methods that do not specify a delimiter.
* The default value of the delimiter is '.' (dot).
*/
public static final String DEFAULT_DELIMITER = ".";
/**
* Prevent from instantiating this class.
*
* @throws InstantiationException thrown when trying to instantiate this class.
*/
private Flat() throws InstantiationException {
throw new InstantiationException("Instances of this type are forbidden");
}
/**
* This method flattens the given JSON object.
* It will use the default delimiter.
* Your keys cannot contain the default delimiter.
*
* @param jsonObject the JSON object to flatten
* @return a string representation of the flattened JSON document.
*/
public static String flatten(JSONObject jsonObject) throws JSONException {
return flatten(jsonObject, DEFAULT_DELIMITER);
}
/**
* This method flattens the string representation of the JSON object.
* It will use the default delimiter.
* Your keys cannot contain the default delimiter.
*
* @param jsonString the string representation of the JSON object.
* @return a string representation of the flattened JSON document.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static String flatten(String jsonString) throws JSONException {
return flatten(jsonString, DEFAULT_DELIMITER);
}
/**
* This method flattens the given JSON object.
* It will use the given delimiter to separate keys and indexes.
* Your keys cannot contain the given delimiter.
*
* Running the following code:
*
* Flat.flatten(new JSONObject("\"key1": { \"nested1\" : 1, \"nested2\" : 2 }}"), "@");
*
*
* will generate:
*
* {
* "key1@nested1" : 1
* "key1@nested2" : 2
* }
*
*
* instead of the default:
*
* {
* "key1.nested1" : 1
* "key1.nested2" : 2
* }
*
*
* @param jsonObject the JSON object to flatten
* @param delimiter the delimiter to use when joining the keys.
* @return a string representation of the flattened JSON document.
*/
public static String flatten(JSONObject jsonObject, String delimiter) throws JSONException {
StringBuilder sb = new StringBuilder();
flatten(sb, null, jsonObject, delimiter);
String s = "{" + sb.toString() + "}";
return s;
}
/**
* This method flattens the string representation of the JSON object.
* It will use the given delimiter to separate keys and indexes.
* Your keys cannot contain the given delimiter.
*
* Running the following code:
*
* Flat.flatten("\"key1": { \"nested1\" : 1, \"nested2\" : 2 }}", "@");
*
*
* will generate:
*
* {
* "key1@nested1" : 1
* "key1@nested2" : 2
* }
*
*
* instead of the default:
*
* {
* "key1.nested1" : 1
* "key1.nested2" : 2
* }
*
*
* @param jsonString the string representation of the JSON object.
* @param delimiter the delimiter to use when joining the keys.
* @return a string representation of the flattened JSON document.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static String flatten(String jsonString, String delimiter) throws JSONException {
JSONObject jsonObject = new JSONObject(jsonString);
return flatten(jsonObject, delimiter);
}
/**
* This method flattens the string representation of the JSON object.
* It will use the default delimiter.
* Your keys cannot contain the default delimiter.
*
* @param jsonString the string representation of the JSON object.
* @return a flattened JSON object.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static JSONObject flattenToJSONObject(String jsonString) throws JSONException {
String flatJsonString = flatten(jsonString);
return new JSONObject(flatJsonString);
}
/**
* This method flattens the given JSON object.
* It will use the default delimiter.
* Your keys cannot contain the default delimiter.
*
* @param jsonObject the JSON object to flatten.
* @return a flattened JSON object.
*/
public static JSONObject flattenToJSONObject(JSONObject jsonObject) throws JSONException {
String flatJsonString = flatten(jsonObject);
return new JSONObject(flatJsonString);
}
/**
* This method flattens the string representation of the JSON object.
* It will use the given delimiter to separate keys and indexes.
* Your keys cannot contain the given delimiter.
*
* @param jsonString the string representation of the JSON object.
* @param delimiter the delimiter to use when joining the keys.
* @return a flattened JSON object.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static JSONObject flattenToJSONObject(String jsonString, String delimiter) throws JSONException {
String flatJsonString = flatten(jsonString, delimiter);
return new JSONObject(flatJsonString);
}
/**
* This method flattens the string representation of the JSON object.
* It will use the given delimiter to separate keys and indexes.
* Your keys cannot contain the given delimiter.
*
* @param jsonObject the JSON object to flatten.
* @param delimiter the delimiter to use when joining the keys.
* @return a flattened JSON object.
*/
public static JSONObject flattenToJSONObject(JSONObject jsonObject, String delimiter) throws JSONException {
String flatJsonString = flatten(jsonObject, delimiter);
return new JSONObject(flatJsonString);
}
/**
* This method flattens the string representation of the JSON object.
*
* @param flattenedJson StringBuilder that will contain the flattened object.
* @param parent parent element of the object.
* @param value object to flatten.
* @param delimiter the delimiter to use when joining the keys.
* @return a string representation of the flattened JSON object.
*/
private static void flatten(StringBuilder flattenedJson, String parent, Object value, String delimiter) throws JSONException {
if (value instanceof JSONObject) {
JSONObject jsonObject = (JSONObject) value;
for (Iterator i = jsonObject.keys(); i.hasNext();) {
String key = i.next();
if (key.contains(delimiter)) {
throw new IllegalArgumentException("A key cannot contain the delimiter");
}
String hkey = (parent == null) ? key : parent + delimiter + key;
Object jval = jsonObject.get(key);
flatten(flattenedJson, hkey, jval, delimiter);
if (i.hasNext()) {
flattenedJson.append(",");
}
}
} else if (value instanceof JSONArray) {
JSONArray jsonArray = (JSONArray) value;
for (int i = 0; i < jsonArray.length(); i++) {
String hkey = (parent == null) ? Integer.toString(i) : parent + delimiter + i;
Object aval = jsonArray.get(i);
flatten(flattenedJson, hkey, aval, delimiter);
if (i < jsonArray.length() - 1) {
flattenedJson.append(",");
}
}
} else if (value instanceof String) {
flattenedJson.append("\"").append(parent).append("\"").append(":");
String s = (String) value;
flattenedJson.append(JSONObject.quote(s));
} else if (value instanceof Integer) {
flattenedJson.append("\"").append(parent).append("\"").append(":");
Integer integer = (Integer) value;
flattenedJson.append(integer);
} else if (JSONObject.NULL.equals(value)) {
flattenedJson.append("\"").append(parent).append("\"").append(":");
flattenedJson.append("null");
}
}
/**
* This method takes the string representation of a flattened JSON object
* and returns it to the conventional format.
* It will use the default delimiter.
*
* @param flatJsonString the string representation of the JSON object.
* @return a string representation of a conventional JSON object.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static String unflatten(String flatJsonString) throws JSONException {
return unflatten(flatJsonString, DEFAULT_DELIMITER);
}
/**
* This method takes a flattened JSON object and returns it to
* the conventional format.
* It will use the default delimiter.
*
* @param flatJsonObject the JSON object to unflatten.
* @return a string representation of a conventional JSON object.
*/
public static String unflatten(JSONObject flatJsonObject) throws JSONException {
return unflatten(flatJsonObject, DEFAULT_DELIMITER);
}
/**
* This method takes the string representation of a flattened JSON object
* and returns it to the conventional format.
* It will use the given delimiter.
*
* @param flatJsonString the JSON object to unflatten.
* @param delimiter the delimiter to use when splitting the keys.
* @return a string representation of a conventional JSON object.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static String unflatten(String flatJsonString, String delimiter) throws JSONException {
JSONObject flatJsonObject = new JSONObject(flatJsonString);
return unflatten(flatJsonObject, delimiter);
}
/**
* This method takes a flattened JSON object and returns it to
* the conventional format.
* It will use the given delimiter.
*
* @param flatJsonObject the JSON object to unflatten.
* @param delimiter the delimiter to use when splitting the keys.
* @return a string representation of a conventional JSON object.
*/
public static String unflatten(JSONObject flatJsonObject, String delimiter) throws JSONException {
return unflattenToJSONObject(flatJsonObject, delimiter).toString();
}
/**
* This method takes the string representation of a flattened JSON object
* and returns it to the conventional format.
* It will use the default delimiter.
*
* @param flatJsonObject the string representation of the JSON object.
* @return a conventional JSON object.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static JSONObject unflattenToJSONObject(String flatJsonObject) throws JSONException {
return unflattenToJSONObject(flatJsonObject, DEFAULT_DELIMITER);
}
/**
* This method takes a flattened JSON object and returns it to
* the conventional format.
* It will use the default delimiter.
*
* @param flatJsonObject the JSON object to unflatten.
* @return a conventional JSON object.
*/
public static JSONObject unflattenToJSONObject(JSONObject flatJsonObject) throws JSONException {
return unflattenToJSONObject(flatJsonObject, DEFAULT_DELIMITER);
}
/**
* This method takes the string representation of a flattened JSON object
* and returns it to the conventional format.
* It will use the given delimiter.
*
* @param flatJsonString the JSON object to unflatten.
* @param delimiter the delimiter to use when splitting the keys.
* @return a conventional JSON object.
* @throws JSONException when the given string cannot be parsed to a JSON object.
*/
public static JSONObject unflattenToJSONObject(String flatJsonString, String delimiter) throws JSONException {
JSONObject flatJsonObject = new JSONObject(flatJsonString);
return unflattenToJSONObject(flatJsonObject, delimiter);
}
/**
* This method takes a flattened JSON object and returns it to
* the conventional format.
* It will use the given delimiter.
*
* @param flatJsonObject the JSON object to unflatten.
* @param delimiter the delimiter to use when splitting the keys.
* @return a conventional JSON object.
*/
public static JSONObject unflattenToJSONObject(JSONObject flatJsonObject, String delimiter) throws JSONException {
JSONObject unflattened = new JSONObject();
for (Iterator keyIterator = flatJsonObject.keys(); keyIterator.hasNext();) {
String flattenedKey = keyIterator.next();
String[] keys = flattenedKey.split(Pattern.quote(delimiter));
Object parent = null;
Object json = unflattened;
for (int i = 0; i < keys.length; i++) {
if (i == keys.length - 1) {
// We are at a leaf key
Object value = flatJsonObject.get(flattenedKey);
if (json instanceof JSONObject) {
JSONObject jsonObject = (JSONObject)json;
jsonObject.put(keys[i], value);
} else if (json instanceof JSONArray) {
JSONArray jsonArray = (JSONArray)json;
if (isNumber(keys[i])) {
int index = Integer.parseInt(keys[i]);
jsonArray.put(index, value);
} else {
// It was not an array after all, convert array to object
JSONObject jsonObject = new JSONObject();
String parentKeyPrefix = parentKeyPrefix(keys, delimiter);
for (int j = 0; j< jsonArray.length(); j++) {
// here we need to check if the leaf we are moving exists and is null
if (!jsonArray.isNull(j) || flatJsonObject.has(parentKeyPrefix + j)) {
Object object = jsonArray.get(j);
jsonObject.put(Integer.toString(j), object);
}
}
if (parent instanceof JSONArray) {
JSONArray array = (JSONArray)parent;
int index = Integer.parseInt(keys[i - 1]);
array.put(index, jsonObject);
} else {
JSONObject object = (JSONObject)parent;
object.put(keys[i - 1], jsonObject);
}
jsonObject.put(keys[i], value);
}
}
} else {
if (json instanceof JSONObject) {
// The last index was an object: we're creating an object in an object
JSONObject jsonObject = (JSONObject)json;
if (jsonObject.has(keys[i])) {
parent = json;
json = jsonObject.get(keys[i]);
} else {
if (isNumber(keys[i + 1])) {
parent = json;
json = new JSONArray();
jsonObject.put(keys[i], json);
} else {
parent = json;
json = new JSONObject();
jsonObject.put(keys[i], json);
}
}
} else if (json instanceof JSONArray) {
// The last index was an array: we're creating an object in an array
JSONArray jsonArray = (JSONArray)json;
if (isNumber(keys[i])) {
int index = Integer.parseInt(keys[i]);
if (!jsonArray.isNull(index)) {
parent = json;
json = jsonArray.get(index);
} else {
if (isNumber(keys[i + 1])) {
parent = json;
json = new JSONArray();
jsonArray.put(index, json);
} else {
parent = json;
json = new JSONObject();
jsonArray.put(index, json);
}
}
} else {
// It was not an array after all, convert array to object
JSONObject jsonObject = convertJSONArrayToJSONObject(jsonArray);
if (parent instanceof JSONArray) {
JSONArray array = (JSONArray)parent;
int index = Integer.parseInt(keys[i - 1]);
array.put(index, jsonObject);
} else {
JSONObject object = (JSONObject)parent;
object.put(keys[i - 1], jsonObject);
}
if (isNumber(keys[i + 1])) {
parent = json;
json = new JSONArray();
jsonObject.put(keys[i], json);
} else {
parent = json;
json = new JSONObject();
jsonObject.put(keys[i], json);
}
}
}
}
}
}
return unflattened;
}
private static boolean isNumber(String s) {
try {
Integer.parseInt(s);
return true;
} catch (NumberFormatException e) {
return false;
}
}
private static String parentKeyPrefix(String[] keys, String delimiter) {
String[] keyRoot = Arrays.copyOf(keys, keys.length-1);
StringBuilder sb = new StringBuilder();
for (int k = 0; k < keyRoot.length; k++) {
sb.append(keyRoot[k]).append(delimiter);
}
return sb.toString();
}
/**
* Copies all the elements of the array into the object.
* Beware that it will skip null values.
*
* @param jsonArray the json array to convert
* @return the jsonObject
*/
private static JSONObject convertJSONArrayToJSONObject(JSONArray jsonArray) {
JSONObject jsonObject = new JSONObject();
for (int k = 0; k< jsonArray.length(); k++) {
if (!jsonArray.isNull(k)) {
Object object = jsonArray.get(k);
jsonObject.put(Integer.toString(k), object);
}
}
return jsonObject;
}
}
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