String转为List，根据分隔符分割

示例：

String sn= "1234,567,8910";
List<String> snList = Arrays.asList(sn.split(","));

1234, 567, 8910
# List转为String，插入分隔符

示例：
``` java
List<String> list =Arrays.asList("123", "321");
String str = list.stream().collect(Collectors.joining(", "));
System.out.println(str);

123, 321