Question 109048 in Json Question posted in
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Json – How to flatten a java object?

I’ve a Java object structure corresponding to following JSON:

{
  "parentClass": {
    "parentField1": "parentFieldValue1",
    "parentField2": "parentFieldValue2",
    "childClass": {
        "childField1": "childFieldValue1",
        "childField2": "childFieldValue2"
    },
    "childClassList": [
      {
        "stringField": "stringField1",
        "integerField": "integerField1"
      },
      {
        "stringField": "stringField2",
        "integerField": "integerField2"
      }
    ]
  }
}

I want to flatten it to following structure:

{
    "parentClass.parentField1": "parentFieldValue1",
    "parentClass.parentField2": "parentFieldValue2",
    "parentClass.childClass.childField1": "childFieldValue1",
    "parentClass.childClass.childField2": "childFieldValue2",
    "parentClass.childClassList[0].stringField": "stringField1",
    "parentClass.childClassList[0].integerField": "integerField1",
    "parentClass.childClassList[1].stringField": "stringField2",
    "parentClass.childClassList[1].integerField": "integerField2"
}

Is there a way to do it?

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    I've found a way using following code:

    convertToFlatMap("", obj, new HashMap<>())

    Implementation:

    private static Map<String, Object> convertToFlatMap(String prefix, Object obj, Map<String, Object> map) {
        if (obj == null) {
            return map;
        }
        if (obj instanceof Map) {
            Map<?, ?> objMap = (Map<?, ?>) obj;
            objMap.forEach((key, value) -> {
                String fullKey = prefix.isEmpty() ? key.toString() : prefix + "." + key.toString();
                convertToFlatMap(fullKey, value, map);
            });
        } else if (obj.getClass().isArray()) {
            Object[] array = (Object[]) obj;
            for (int i = 0; i < array.length; i++) {
                String fullKey = prefix + "[" + i + "]";
                convertToFlatMap(fullKey, array[i], map);
            }
        } else if (obj instanceof Iterable) {
            Iterable<?> iterable = (Iterable<?>) obj;
            int i = 0;
            for (Object item : iterable) {
                String fullKey = prefix + "[" + i + "]";
                convertToFlatMap(fullKey, item, map);
                i++;
            }
        } else if (obj.getClass().isPrimitive() || obj instanceof String) {
            map.put(prefix, obj);
        } else {
            // recursively flatten nested object properties
            Map<String, Object> nestedMap = new HashMap<>();
            for (java.lang.reflect.Field field : obj.getClass().getDeclaredFields()) {
                field.setAccessible(true);
                String fullKey = prefix.isEmpty() ? field.getName() : prefix + "." + field.getName();
                try {
                    Object fieldValue = field.get(obj);
                    convertToFlatMap(fullKey, fieldValue, nestedMap);
                } catch (IllegalAccessException e) {
                    throw new RuntimeException("Error accessing field " + field.getName() + " of object " + obj.getClass().getName());
                }
            }
            map.putAll(nestedMap);
        }
        return map;
    }

  2. 0

    Library Josson has function flatten() to do the transformation.

    https://github.com/octomix/josson

    Josson josson = Josson.fromJsonString(
    "{" +
    "  "parentClass": {" +
    "    "parentField1": "parentFieldValue1"," +
    "    "parentField2": "parentFieldValue2"," +
    "    "childClass": {" +
    "        "childField1": "childFieldValue1"," +
    "        "childField2": "childFieldValue2"" +
    "    }," +
    "    "childClassList": [" +
    "      {" +
    "        "stringField": "stringField1"," +
    "        "integerField": "integerField1"" +
    "      }," +
    "      {" +
    "        "stringField": "stringField2"," +
    "        "integerField": "integerField2"" +
    "      }" +
    "    ]" +
    "  }" +
    "}");
JsonNode node = josson.getNode("flatten('.', '[%d]')");
System.out.println(node.toPrettyString());

    Output

    {
  "parentClass.parentField1" : "parentFieldValue1",
  "parentClass.parentField2" : "parentFieldValue2",
  "parentClass.childClass.childField1" : "childFieldValue1",
  "parentClass.childClass.childField2" : "childFieldValue2",
  "parentClass.childClassList[0].stringField" : "stringField1",
  "parentClass.childClassList[0].integerField" : "integerField1",
  "parentClass.childClassList[1].stringField" : "stringField2",
  "parentClass.childClassList[1].integerField" : "integerField2"
}
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