把逗号分隔的String字符串转List<Integer>

• 把逗号分隔的String字符串转int集合
• 集合或数组转变为逗号分隔的字符串的几种方式
• 1、自己编码实现
• 2、org.apache.commons.lang3.StringUtils
• 3、StringJoiner, JDK1.8+
• 4、String.join(), JDK1.8+
• 5、Stream, Collectors.joining(), JDK1.8+

把逗号分隔的String字符串转int集合

代码通过Java 8 Stream实现起来非常容易！

1. String ids = "1,2,3,4,5";
2. List<Integer> idList = Arrays.stream(ids.split(",")).map(Integer::parseInt).collect(Collectors.toList());

集合或数组转变为逗号分隔的字符串的几种方式

首先，创建一个集合

1. List<String> list = Lists.newArrayList(null, "bob", "jack");

1、自己编码实现

1. public static <T> String join(List<T> list, String splitStr) {
2. if (CollectionUtils.isEmpty(list))
3. return "";
4. if (list.size() == 1)
5. return String.valueOf(list.get(0));
6. StringBuilder sb = new StringBuilder();
7. boolean isFirst = true;
8. for (int i = 0; i < list.size(); i++) {
9. if (!isFirst) sb.append(splitStr);
10. sb.append(String.valueOf(list.get(i)));
11. isFirst = false;
12. }
13. return sb.toString();
14. }
15. public static <T> String join(T[] array, String splitStr) {
16. if (ArrayUtils.isEmpty(array))
17. return "";
18. if (array.length == 1)
19. return String.valueOf(array[0]);
20. StringBuilder sb = new StringBuilder();
21. boolean isFirst = true;
22. for (int i = 0; i < array.length; i++) {
23. if (!isFirst) sb.append(splitStr);
24. sb.append(String.valueOf(array[i]));
25. isFirst = false;
26. }
27. return sb.toString();
28. }

输出

null,bob,jack

2、org.apache.commons.lang3.StringUtils

1. System.out.println(StringUtils.join(list.toArray(), ","));

输出

,bob,jack

3、StringJoiner, JDK1.8+

1. StringJoiner sj = new StringJoiner(",");
2. list.forEach(e -> sj.add(String.valueOf(e)));
3. System.out.println(sj.toString());
4. // 在连接之前操作字符串, 拼接前缀和后缀
5. StringJoiner sj2 = new StringJoiner(",", "START_", "_END");
6. list.forEach(e -> sj2.add(String.valueOf(e)));
7. System.out.println(sj2.toString());

输出

null,bob,jack
START_null,bob,jack_END

4、String.join(), JDK1.8+

1. System.out.println(String.join(",", list));

输出

null,bob,jack

5、Stream, Collectors.joining(), JDK1.8+

1. System.out.println(list.stream().collect(Collectors.joining(",")));
2. // 在连接之前操作字符串, 拼接前缀和后缀
3. String str = list.stream().map(e -> {
4. if (e != null) return e.toUpperCase();
5. else return "null";
6. }).collect(Collectors.joining(",", "START_", "_END"));
7. System.out.println(str);

输出

null,bob,jack
START_null,BOB,JACK_END