java8 stream .skip() .limit() 实现分页功能
先分别介绍一下 skip() 和 limit():
skip()用法：
skip(long n) 是一个跳过前 n 个元素的中间流操作。
public static void skip(long n) {
Stream<Integer> integerStream = Stream.of(1, 2, 3, 4, 5, 6);
integerStream.skip(n).forEach(integer -> System.out.println("integer = " + integer));
}
结果：
-
当 n < 0 时直接抛出了 IllegalArgumentException 异常；
-
当 n=0 时，打印出1，2，3，4，5，6；
-
当 n=3 时，打印了 4, 5 ,6 ；
-
当n>6时，打印为空；
也就是说 skip(long n) 方法跳过前 n （非负）个元素，返回剩下的流。
limit()
limit(long n) 限制打印出的数据个数为n
public static void limit(long n) {
Stream<Integer> integerStream = Stream.of(1, 2, 3, 4, 5, 6);
integerStream.limit( maxsize).forEach(integer -> System.out.println("integer = " + integer));
}
结果：
- 当 n < 0 时直接抛出了 IllegalArgumentException 异常;
- 当 n=0 时，返回为空；
- 当 n=4 时，打印了 1 、 2 、3 、 4 ；
- n=8 时，打印了所有元素；用法跟上面的skip()有相似之处。
正文：
使用上面两个方法 skip(), limit() 实现分页：
public static void main(String[] args) {
List<Integer> list = new ArrayList();
for(int i=1; i<10; i++){
list.add(i);
}
Scanner input =new Scanner(System.in);
System.out.println("请输入当前页数：");
int page =input.nextInt();
System.out.println("请输入每页显示个数：");
int limit = input.nextInt();
System.out.println("第" + page + "页数据:" + getPageResult(list, page, limit));
}
/**
* 分页方法
*
* @param list 要分页的数据
* @param page 当前页
* @param size 每页条数
*/
public static List<Integer> getPageResult(List<Integer> list, int page, int size) {
//模拟分页效果
return list.stream().skip((page - 1) * size)
.limit(size)
.collect(Collectors.toList());
}
测试结果：
请输入当前页数：
1
请输入每页显示个数：
5
第1页数据:[1, 2, 3, 4, 5]
再测：
请输入当前页数：
2
请输入每页显示个数：
5
第2页数据:[6, 7, 8, 9]
注意：
简单的数据类型的分页或者量小的数据可以使用，但是复杂的数据类型分页不推荐这种，随着数据的增多，效率会变得比较慢。
粗略测试一下简单数据类型的时间消耗，仅供参考：
public static void main(String[] args) {
List<Integer> list = new ArrayList();
long time1 = System.currentTimeMillis();
String format1 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(time1);
System.out.println("开始装入list数据："+format1);
for(int i=1;i<99999999;i++){
list.add(i);
}
long time2 = System.currentTimeMillis();
String format2 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(time2);
System.out.println("装入list数据完毕："+format2);
long time3 = (time2-time1)/1000;
System.out.println("将99999999个数字放入list耗时"+time3+"秒！");
Scanner input =new Scanner(System.in);
System.out.println("请输入当前页数：");
int page =input.nextInt();
System.out.println("请输入每页显示个数：");
int limit = input.nextInt();
long time4 = System.currentTimeMillis();
String format4 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(time4);
System.out.println("开始分页："+format4);
System.out.println("第" + page + "页数据:" + getPageResult(list, page, limit));
long time5 = System.currentTimeMillis();
String format5 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(time5);
System.out.println("结束分页："+format5);
long time6 = (time5-time4);
System.out.println("分页耗时"+time6+"毫秒！");
}
/**
* 分页方法
*
* @param list 要分页的数据
* @param page 当前页
* @param size 每页条数
*/
public static List<Integer> getPageResult(List<Integer> list, int page, int size) {
//模拟分页效果
return list.stream().skip((page - 1) * size)
.limit(size)
.collect(Collectors.toList());
}
测试结果：
开始装入list数据：2020-10-24 22:42:29
装入list数据完毕：2020-10-24 22:43:01
将99999999个数字放入list耗时31秒！
请输入当前页数：
6
请输入每页显示个数：
10
开始分页：2020-10-24 22:43:13
第6页数据:[51, 52, 53, 54, 55, 56, 57, 58, 59, 60]
结束分页：2020-10-24 22:43:13
分页耗时31毫秒！
再测：
开始装入list数据：2020-10-24 22:44:56
装入list数据完毕：2020-10-24 22:45:28
将99999999个数字放入list耗时31秒！
请输入当前页数：
50
请输入每页显示个数：
1000
开始分页：2020-10-24 22:45:37
第50页数据:[49001, 49002, 49003, 49004, 49005, 49006, 49007, 49008, 49009, 49010, 49011, 49012, 49013, 49014, 49015, 49016, 49017, 49018, 49019, 49020, 49021, 49022, 49023, 49024, 49025, 49026, 49027, 49028, 49029, 49030, 49031, 49032, 49033, 49034, 49035, 49036, 49037, 49038, 49039, 49040, 49041, 49042, 49043, 49044, 49045, 49046, 49047, 49048, 49049, 49050, 49051, 49052, 49053, 49054, 49055, 49056, 49057, 49058, 49059, 49060, 49061, 49062, 49063, 49064, 49065, 49066, 49067, 49068, 49069, 49070, 49071, 49072, 49073, 49074, 49075, 49076, 49077, 49078, 49079, 49080, 49081, 49082, 49083, 49084, 49085, 49086, 49087, 49088, 49089, 49090, 49091, 49092, 49093, 49094, 49095, 49096, 49097, 49098, 49099, 49100, 49101, 49102, 49103, 49104, 49105, 49106, 49107, 49108, 49109, 49110, 49111, 49112, 49113, 49114, 49115, 49116, 49117, 49118, 49119, 49120, 49121, 49122, 49123, 49124, 49125, 49126, 49127, 49128, 49129, 49130, 49131, 49132, 49133, 49134, 49135, 49136, 49137, 49138, 49139, 49140, 49141, 49142, 49143, 49144, 49145, 49146, 49147, 49148, 49149, 49150, 49151, 49152, 49153, 49154, 49155, 49156, 49157, 49158, 49159, 49160, 49161, 49162, 49163, 49164, 49165, 49166, 49167, 49168, 49169, 49170, 49171, 49172, 49173, 49174, 49175, 49176, 49177, 49178, 49179, 49180, 49181, 49182, 49183, 49184, 49185, 49186, 49187, 49188, 49189, 49190, 49191, 49192, 49193, 49194, 49195, 49196, 49197, 49198, 49199, 49200, 49201, 49202, 49203, 49204, 49205, 49206, 49207, 49208, 49209, 49210, 49211, 49212, 49213, 49214, 49215, 49216, 49217, 49218, 49219, 49220, 49221, 49222, 49223, 49224, 49225, 49226, 49227, 49228, 49229, 49230, 49231, 49232, 49233, 49234, 49235, 49236, 49237, 49238, 49239, 49240, 49241, 49242, 49243, 49244, 49245, 49246, 49247, 49248, 49249, 49250, 49251, 49252, 49253, 49254, 49255, 49256, 49257, 49258, 49259, 49260, 49261, 49262, 49263, 49264, 49265, 49266, 49267, 49268, 49269, 49270, 49271, 49272, 49273, 49274, 49275, 49276, 49277, 49278, 49279, 49280, 49281, 49282, 49283, 49284, 49285, 49286, 49287, 49288, 49289, 49290, 49291, 49292, 49293, 49294, 49295, 49296, 49297, 49298, 49299, 49300, 49301, 49302, 49303, 49304, 49305, 49306, 49307, 49308, 49309, 49310, 49311, 49312, 49313, 49314, 49315, 49316, 49317, 49318, 49319, 49320, 49321, 49322, 49323, 49324, 49325, 49326, 49327, 49328, 49329, 49330, 49331, 49332, 49333, 49334, 49335, 49336, 49337, 49338, 49339, 49340, 49341, 49342, 49343, 49344, 49345, 49346, 49347, 49348, 49349, 49350, 49351, 49352, 49353, 49354, 49355, 49356, 49357, 49358, 49359, 49360, 49361, 49362, 49363, 49364, 49365, 49366, 49367, 49368, 49369, 49370, 49371, 49372, 49373, 49374, 49375, 49376, 49377, 49378, 49379, 49380, 49381, 49382, 49383, 49384, 49385, 49386, 49387, 49388, 49389, 49390, 49391, 49392, 49393, 49394, 49395, 49396, 49397, 49398, 49399, 49400, 49401, 49402, 49403, 49404, 49405, 49406, 49407, 49408, 49409, 49410, 49411, 49412, 49413, 49414, 49415, 49416, 49417, 49418, 49419, 49420, 49421, 49422, 49423, 49424, 49425, 49426, 49427, 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50000]
结束分页：2020-10-24 22:45:37
分页耗时38毫秒！