使用Java中的Regex在字符串中查找12小时格式的时间

Question

I'm trying to find a time in a String using a regex in Java. Here's the regex:

\d{1,2}?:\d\d(?)(am|pm)??

That should look for 1 or 2 digits, followed by a colon, two more digits, then either "am" or "pm" (irrespective of case).

It mostly works, but if I wrap that entire regex in a capture group, I only get hh:mm. For example, "12:34am" returns just "12:34". No "am".

UPDATE: Full code example

Pattern p = Pattern.compile("\\d{1,2}?:\\d\\d(?)(am|pm)??");
Matcher matcher = p.matcher("12:34AM");
Assert.assertTrue(matcher.find());
Assert.assertEquals("12:34AM", matcher.group());

Anyone have any idea why?

Answer 1

Instead of your current pattern, you might want to use \\b(?:[01]?\\d|2[0-3]):[0-5]?\\d(?:[ap]m)?\\b to match times, with the case-insensitive flag set or even use alternatives to distinct between 24h notation and 12h notation with am / pm

Your current pattern uses a lazy optional pattern to match the am / pm ( (am|pm)?? ), as this is at the end of the pattern, it will never match (except when used in the context of .matches() instead of .find(), as it forces a full match).

I'm honestly not sure about the (?) in your pattern.

Answer 2

This gets your group correctly with modifications to the test string to match case, remove extraneous question marks and to add the surrounding group.

Pattern p = Pattern.compile("(\\d{1,2}:\\d\\d(AM|PM)?)");
Matcher matcher = p.matcher("12:34AM");
Assert.assertTrue(matcher.find());
Assert.assertEquals("12:34AM", matcher.group());

Answer 3

As you are matching against 12 hour format so there are many bound to cover so never use \\d because it will accept any number number input given by user and your regex will fail against these invalid cases like 13:32am 22:23am or many others non-12 hour formats

so to make it robust use

\\\\b(1[012]|0[1-9]):([0-5][0-9])(\\\\s)?([Aa]|[pP])[mM]

\\\\b(1[012]|0?[1-9]): \\\\b word boundary then either 10,11,12 or 0 with 1-9

:([0-5][0-9]) : character match digits from 00-59

(\\\\s)? there can be a single space

([Aa]|[pP])[mM] either am,AM or pm,PM etc

Complete code would be

    Pattern pattern=Pattern.compile("\\b(1[012]|0[1-9]):([0-5][0-9])(\\s)?([Aa]|[pP])[mM]");
    Matcher matcher=pattern.matcher("12:23am 12:6am  ds  13:32am dwdw c 01:12am ded 1:21am");

    while (matcher.find()) {
        System.out.println(matcher.group());
    } 

To make it more flexible for inputs like 1:21am and 1:1am use

\\\\b(1[012]|0?[1-9]):([0-5]?[0-9])(\\\\s)?([Aa]|[pP])[mM]

Answer 4

抱歉，我编辑了以下内容： \\d?\\d:\\d?\\d["a"|"p"|"A"|"P"]["m"|"M"]