String 转 List<Long>

String string = "1, 2, 3, 4";
List<Long> list = Arrays.asList(string.split(",")).stream().map(s -> Long.parseLong(s.trim())).collect(Collectors.toList());

List<Long> 转 String

String str = Arrays.toString(listIds.toArray());   //[1,2,3,3,4]

List<String> list = new ArrayList<>(2);
list.add("guan");
list.add("bao");
String[] array = list.toArray(new String[0]);

String[] str = new String[] { "yang", "hao" };

List list = Arrays.asList(str);

仍然为数组，不可使用add/remove/clear方法。