public String eval(String field, String key) {
        try {
            return mapper.readTree(field).findValue(key).asText();
        } catch (Exception e) {
            LOG.error("json getter function error, key {}, field {}", key, field, e);
            return null;
        }
    }
eval is String replacement execution method

@param field is the field to be replaced
@return replaced value
inlong-sort/sort-core/src/main/java/org/apache/inlong/sort/function/JsonGetterFunction.java