How should I convert the case of a JSON payload to lower camel case?

Question

I'm dealing with JSON whose property names are snake-cased, but, I need these transformed into a lower camel case.

I don't have beans for all the corresponding objects so the usual ser-de tricks of Jackson don't apply (I think).

I tried reading it into a Map and setting a global property naming strategy but that didn't work.

    String json = "{\"first_name\": \"John\", \"last_name\": \"Doe\" }";

    Map<?, ?> myMap = new ObjectMapper().readValue(json, Map.class);
    System.out.println(new ObjectMapper()
            .setPropertyNamingStrategy(new UpperCamelCaseStrategy())
            .writerWithDefaultPrettyPrinter()
            .writeValueAsString(myMap));

I don't need this to be necessarily accomplished in Jackson. While a simple problem, it did leave me quite lost as to what a sane way of accomplishing this might be.

Answer 1

I found this solution, which is a bit hard-coded, using regex. In this way, however, you do not need to use any JsonObject library.

I wrote three methods:

1. one to convert a string from snake_case to pascalCase

    private static String convertToPascalCase(String str){ while(str.contains("_")) { str = str.replaceFirst("_[az]", String.valueOf(Character.toUpperCase(str.charAt(str.indexOf("_") + 1)))); } return str; }

2. Another which handles the replacing of the regex matches

   private static String replaceMatches(Matcher m, Function<MatchResult, String> mapping) { StringBuffer sb = new StringBuffer(); while (m.find()) { MatchResult matchResult = m.toMatchResult(); m.appendReplacement(sb, mapping.apply(matchResult)); } m.appendTail(sb); return sb.toString(); }

3. the last one which defines the appropriate regex and then calls replaceMatches

    public static String convertToPascalCaseAllJsonKeys(String jsonString) { Pattern p = Pattern.compile("\"(\\w+)\":"); Matcher m = p.matcher(jsonString); return replaceMatches(m, mr -> "\"" + convertToPascalCase(mr.group(1)) + "\":"); }

The usage is the following:

String json = "{\"first_name\": \"John\", \"last_name\": \"Doe\", \"children\": [\"Jane\", \"Mary\", \"Harry\"]}";
String jsonWithPascalKey = convertToPascalCaseAllJsonKeys(json);

System.out.println(jsonWithPascalKey );
// result: {"firstName": "John", "lastName": "Doe", "children": ["Jane", "Mary", "Harry"]}

Then, you can easily convert the string to a JsonObject.

Answer 2

https://github.com/octomix/josson

If the JSON has one level.

Josson josson = Josson.fromJsonString("{\"first_name\": \"John\", \"last_name\": \"Doe\"}");
JsonNode node = josson.getNode("entries().map(key.camelCase()::value).mergeObjects()");
System.out.println(node.toPrettyString());

Output

{
  "firstName" : "John",
  "lastName" : "Doe"
}

Nest the transformation query one more time for each additional level.

Josson josson = Josson.fromJsonString("{\"sales_person\":{\"first_name\": \"John\", \"last_name\": \"Doe\"}}");
JsonNode node = josson.getNode(
    "entries()" +
    ".map(key.camelCase()" +
    "     ::value.entries()" +
    "       .map(key.camelCase()" +
    "            ::value)" +
    "       .mergeObjects())" +
    ".mergeObjects()");
System.out.println(node.toPrettyString());

Output

{
  "salesPerson" : {
    "firstName" : "John",
    "lastName" : "Doe"
  }
}