1410 google 2006-05-01 21:40:54 1 http://www.google.com
2005 google 2006-03-24 21:25:10 1 http://www.google.com
2005 google 2006-03-26 21:58:12
2178 google 2006-03-27 20:58:44 1 http://www.google.com
2178 google 2006-04-11 11:06:20
2178 google 2006-04-11 11:06:41
2178 google 2006-05-16 10:54:39 1 http://www.google.com
2421 google 2006-05-04 15:39:25 1 http://www.google.com
2421 google 2006-05-04 21:14:33 1 http://www.google.com
2421 google 2006-05-05 16:16:01
2722 google 2006-04-12 15:18:12 1 http://www.google.com
2722 google 2006-05-02 09:09:19 1 http://www.google.com
2722 google 2006-05-25 15:42:26 1 http://www.google.com
2722 google 2006-05-25 15:42:26 1 http://www.google.com
6497 google 2006-04-06 22:47:10 1 http://www.google.com
6497 google 2006-04-06 23:05:58 1 http://www.google.com
9777 google 2006-03-11 23:25:57 1 http://www.google.com
9844 google 2006-03-19 10:31:09
9844 google 2006-03-19 10:31:12 1 http://www.google.com
12404 google 2006-03-04 00:42:26 1 http://www.google.com
12404 google 2006-03-13 21:17:22 1 http://www.google.com
12404 google 2006-03-13 21:17:22 1 http://www.google.com
12404 google 2006-03-13 21:17:22 1 http://www.google.com
12404 google 2006-03-13 21:17:22 1 http://www.google.com
12404 google 2006-03-13 21:47:04 1 http://www.google.com
12404 google 2006-03-13 21:47:04 1 http://www.google.com
12404 google 2006-03-22 16:57:44 1 http://www.google.com
12404 google 2006-03-23 22:07:33 1 http://www.google.com
12404 google 2006-03-23 22:07:33 1 http://www.google.com
12404 google 2006-03-23 22:07:33 1 http://www.google.com
考虑到上面的搜索查询块，我想提取两件事：首先，随机选择一个用户（基于id），其次，我想提取相应用户的第一个和最后一个时间戳。我用以下正则表达式给出了类似的答案：
private static final Pattern LINE_REGEX = Pattern.compile(
"[0-9]+" // user id
+ "\\s+" // space after user id
+ "(.*?[^\\s])" // user name (group 1)
+ "\\s+" // space after user name
+ "([0-9]+-.{14})" // timestamp (group 2)
+ "\\s+" //space after timestamp
+ "[0-9]*" // random int
+ "\\s+" //space after random int
+ "(.*[^\\s])" // user action (group 3)
）;
try(Stream<String> stream = Files.lines(Paths.get("file name"))) {
result = stream.map(LINE_REGEX::matcher)
// filter out any lines without an Action
.filter(Matcher::matches)
// group by User
.collect(Collectors.groupingBy((Matcher m) -> m.group(1),
Collectors.collectingAndThen(
// compare Timestamp (min for earliest, max for latest)
Collectors.maxBy(Comparator.comparing((Matcher m) -> m.group(2))),
// extract Action
(Optional<Matcher> m) -> m.get().group(3))));
}
但是有两个问题，首先它会按照关键字分组（在我的情况下）而不是用户的id;其次，如果我使用.minBy()，它将获得其他一些随机用户的第一个时间戳。与.maxBy()不是同一个用户。
知道如何解决这个问题吗？
答案 0 :(得分：0)
您当前正按USERNAME（或关键字）对用户进行分组，而不是用户ID。由于用户名始终为＆＃34; google＆＃34;，因此所有行都在一个组中。
将正则表达式的第一部分（用户ID）放在括号中;并删除用户名部分周围的组括号或增加时间戳和操作的组索引。
private static final Pattern LINE_REGEX = Pattern.compile(
"([0-9]+)" // user id <- parentheses go here
+ "\\s+" // space after user id
+ ".*?[^\\s]" // user name (group 1) <- not here
+ "\\s+" // space after user name
+ "([0-9]+-.{14})" // timestamp (group 2)
+ "\\s+" //space after timestamp
+ "[0-9]*" // random int
+ "\\s+" //space after random int
+ "(.*[^\\s])" // user action (group 3)
);
如果您需要关键字/用户名，您也可以将其保留为一个组，然后再向匹配器询问keyword/username + action。
另请注意，您目前通过字符串比较来排序时间戳（但这种格式对此特定格式有效）。
编辑：我将添加一个完整的示例。
Pattern LINE_REGEX = Pattern.compile("([0-9]+)" // user id (group 1)
+ "\\s+" // space after user id
+ "(.*?[^\\s])" // user name (group 2)
+ "\\s+" // space after user name
+ "([0-9]+-.{14})" // timestamp (group 3)
+ "\\s+" // space after timestamp
+ "([0-9]*)" // random int (group 4)
+ "\\s+" // space after random int
+ "(.*[^\\s])" // user action (group 5)
);
Stream<String> lines = Stream.of("1410 google 2006-05-01 21:40:54 1 http://www.google.com",
"2005 google 2006-03-24 21:25:10 1 http://www.google.com", "2005 google 2006-03-26 21:58:12",
"2178 google 2006-03-27 20:58:44 1 http://www.google.com", "2178 google 2006-04-11 11:06:20",
"2178 google 2006-04-11 11:06:41", "2178 google 2006-05-16 10:54:39 1 http://www.google.com",
"2421 google 2006-05-04 15:39:25 1 http://www.google.com", "2421 google 2006-05-04 21:14:33 1 http://www.google.com",
"2421 google 2006-05-05 16:16:01", "2722 google 2006-04-12 15:18:12 1 http://www.google.com",
"2722 google 2006-05-02 09:09:19 1 http://www.google.com", "2722 google 2006-05-25 15:42:26 1 http://www.google.com",
"2722 google 2006-05-25 15:42:26 1 http://www.google.com", "6497 google 2006-04-06 22:47:10 1 http://www.google.com",
"6497 google 2006-04-06 23:05:58 1 http://www.google.com", "9777 google 2006-03-11 23:25:57 1 http://www.google.com",
"9844 google 2006-03-19 10:31:09", "9844 google 2006-03-19 10:31:12 1 http://www.google.com",
"12404 google 2006-03-04 00:42:26 1 http://www.google.com", "12404 google 2006-03-13 21:17:22 1 http://www.google.com",
"12404 google 2006-03-13 21:17:22 1 http://www.google.com", "12404 google 2006-03-13 21:17:22 1 http://www.google.com",
"12404 google 2006-03-13 21:17:22 1 http://www.google.com", "12404 google 2006-03-13 21:47:04 1 http://www.google.com",
"12404 google 2006-03-13 21:47:04 1 http://www.google.com", "12404 google 2006-03-22 16:57:44 1 http://www.google.com",
"12404 google 2006-03-23 22:07:33 1 http://www.google.com", "12404 google 2006-03-23 22:07:33 1 http://www.google.com",
"12404 google 2006-03-23 22:07:33 1 http://www.google.com");
Map<String, Matcher> result =
lines.map(LINE_REGEX::matcher)
.filter(Matcher::matches)
.collect(Collectors.groupingBy((Matcher m) -> m.group(1),
Collectors.collectingAndThen(Collectors.maxBy(Comparator.comparing((Matcher m) -> m.group(2))),
Optional<Matcher>::get)));
result.forEach((k, v) -> System.out.println(v.group(0) + ": " + v.group(1) + " " + v.group(2) + " "
+ v.group(3) + " " + v.group(4) + " " + v.group(5)));
--------- Output ---------------
2722: 2722 google 2006-04-12 15:18:12 1 http://www.google.com
9777: 9777 google 2006-03-11 23:25:57 1 http://www.google.com
2005: 2005 google 2006-03-24 21:25:10 1 http://www.google.com
9844: 9844 google 2006-03-19 10:31:12 1 http://www.google.com
6497: 6497 google 2006-04-06 22:47:10 1 http://www.google.com
1410: 1410 google 2006-05-01 21:40:54 1 http://www.google.com
2421: 2421 google 2006-05-04 15:39:25 1 http://www.google.com
2178: 2178 google 2006-03-27 20:58:44 1 http://www.google.com
12404: 12404 google 2006-03-04 00:42:26 1 http://www.google.com
我现在将该行的每个部分都包装在一个捕获组中（有关详细信息，请阅读Pattern文档）。这样，您可以通过向匹配器询问组来访问它。
按照它们在正则表达式中出现的顺序枚举这些组，从1开始。要求matcher.group(0)返回整行。