如何用Java解析1或2位数的小时字符串? [英] How to parse a 1 or 2 digit hour string with Java?

问题描述

我的解析器可能遇到"2:37 PM"(由"H:mma"解析)或"02:37 PM"(由"hh:mma"解析).如何在不借助try-catch的情况下解析两者?

My parser may encounter "2:37PM" (parsed by "H:mma") or "02:37PM" (parsed by "hh:mma"). How can I parse both without resorting to a try-catch?

如果我弄错了，我会收到这样的错误:

I receive an error like this when I get it wrong:

发现冲突:字段AmPmOfDay 0与派生的AmPmOfDay 1不同从02:37

Conflict found: Field AmPmOfDay 0 differs from AmPmOfDay 1 derived from 02:37

推荐答案

首先，您收到的错误是由模式中的 H 引起的，它以24小时格式解析小时，如果在模式末尾放置 a (用于AM/PM)，则会遇到麻烦.

First of all, the error you get is caused by the H in your pattern, which parses hours in 24-hour format and gets into trouble if you put an a (for AM/PM) at the end of the pattern.

您可以使用考虑了 DateTimeFormatter 的 java.time 将 String 解析为 LocalTime 两种模式:

You can use java.time to parse the Strings to LocalTimes using a DateTimeFormatter that considers both of the patterns:

public static void main(String[] args) {
    // define a formatter that considers two patterns
    DateTimeFormatter parser = DateTimeFormatter.ofPattern("[h:mma][hh:mma]");
    // provide example time strings
    String firstTime = "2:37PM";
    String secondTime = "02:37PM";
    // parse them both using the formatter defined above
    LocalTime firstLocalTime = LocalTime.parse(firstTime, parser);
    LocalTime secondLocalTime = LocalTime.parse(secondTime, parser);
    // print the results
    System.out.println("First:\t" + firstLocalTime.format(DateTimeFormatter.ISO_TIME));
    System.out.println("Second:\t" + secondLocalTime.format(DateTimeFormatter.ISO_TIME));
}

它的输出是

First:  14:37:00
Second: 14:37:00

但是事实证明，您只需要一种模式(总之，在 DateTimeFormatter 中要比两个模式更好)，因为 h 可以解析一个小时或一个小时的时间.两位数.因此，以下代码将产生与上面完全相同的输出:

But it turned out you only need one pattern (which is better to have than two in a DateTimeFormatter anyway) because the h is able to parse hours of one or two digits. So the following code produces exactly the same output as the one above:

public static void main(String[] args) {
    // define a formatter that considers hours consisting of one or two digits plus AM/PM
    DateTimeFormatter parser = DateTimeFormatter.ofPattern("h:mma");
    // provide example time strings
    String firstTime = "2:37PM";
    String secondTime = "02:37PM";
    // parse them both using the formatter defined above
    LocalTime firstLocalTime = LocalTime.parse(firstTime, parser);
    LocalTime secondLocalTime = LocalTime.parse(secondTime, parser);
    // print the results
    System.out.println("First:\t" + firstLocalTime.format(DateTimeFormatter.ISO_TIME));
    System.out.println("Second:\t" + secondLocalTime.format(DateTimeFormatter.ISO_TIME));
}

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