limit the size of the string value of all keys with Jackson

Question

I have a dynamic nested json string and I wanted to limit the string value of all keys to have max length of 5 chars.

Using: Java fasterxml.jackson

For Json String like below:

String inputJsonString = "{\"key1\":\"bla bla bla bla\",\"key2\":{\"key21\":\"bla bla bla\"}}";

I wanted this result:

String outputJsonString = "{\"key1\":\"bla b\",\"key2\":{\"key21\":\"bla b\"}}";

For Json String like this:

String inputJsonString = "{\"fname\":\"bla bla bla bla\",\"address\":{\"street\":\"bla bla bla\"}}";

I wanted this result:

String outputJsonString = "{\"fname\":\"bla b\",\"address\":{\"street\":\"bla b\"}}";

Answer 1

Try this.

public static void main(String[] args) throws JsonMappingException, JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper();
    String inputJsonString = "{\"key1\":\"bla bla bla bla\",\"key2\":{\"key21\":\"bla bla bla\"},\"key3\":[{\"key21\":\"bla bla bla\"}]}";
    System.out.println(inputJsonString);
    JsonNode jsonNode = mapper.readTree(inputJsonString);

    truncateStringValues(jsonNode);

    System.out.println(jsonNode);

}

private static void truncateStringValues(JsonNode jsonNode) throws JsonMappingException, JsonProcessingException {
    if (jsonNode.isArray()) {
        for (JsonNode arrayItem : jsonNode) {
            truncateStringValues(arrayItem);
        }

    } else if (jsonNode.isObject()) {
        Iterator<Entry<String, JsonNode>> fields = jsonNode.fields();
        while (fields.hasNext()) {
            Entry<String, JsonNode> jsonField = fields.next();
            JsonNode jsonFieldValue = jsonField.getValue();
            if (!jsonFieldValue.isContainerNode()) {
                ((ObjectNode) jsonNode).put(jsonField.getKey(), jsonFieldValue.asText().substring(0, 5));
            } else {
                truncateStringValues(jsonFieldValue);
            }
        }
    }
}

Answer 2

Nice answer, @John Williams!

Just a quick note: If the string to be truncated is less than 5 characters, there's a chance of encountering java.lang.StringIndexOutOfBoundsException. To handle this, you can use Math.min with substring. Here's an example:

String text = jsonFieldValue.asText();
objectNode.put(entry.getKey(), text.substring(0, Math.min(text.length(), 5)));

This ensures safe truncation. Thanks!