JAVA / Array(배열)을 구분자(콤마 등)를 포함한 문자열로 변경

StringUtils.join(배열, ',');

or

String test = String.join("|", list_acc);

String returnedItems = "a,b,c";
List<String> sellItems = Arrays.asList(returnedItems.split(","));

Now iterate over the list and append each item to a StringBuilder:

StringBuilder sb = new StringBuilder();
for(String item: sellItems){
    if(sb.length() > 0){
        sb.append(',');
    }
    sb.append(item);
}
String result = sb.toString();