Java 8 LocalDateTime 正在解析无效日期

Question

我想在客户端验证日期，所以我编写了以下代码。但是，我没有得到异常，而是得到了 2 月 31 日日期字符串的正确日期对象，这显然是一个无效的日期。

public class Test {

    public static void main(String[] args) {
        String dateFormat = "HH:mm:ss MM/dd/yyyy";
        String dateString = "11:30:59 02/31/2015";
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(dateFormat, Locale.US);
        try {
            LocalDateTime date = LocalDateTime.parse(dateString, dateTimeFormatter);
            System.out.println(date);
        } catch (Exception e) {
            // Throw invalid date message
        }
    }
}

输出:2015-02-28T11:30:59

有谁知道为什么 LocalDateTime 解析这个日期而不是抛出异常。

Answer 1

你只需要一个严格的 ResolverStyle .

Parsing a text string occurs in two phases. Phase 1 is a basic text parse according to the fields added to the builder. Phase 2 resolves the parsed field-value pairs into date and/or time objects. This style is used to control how phase 2, resolving, happens.

示例代码 - 其中 withResolverStyle(ResolverStyle.STRICT) 是重要的变化，同时使用 uuuu 而不是 yyyy(其中uuuu 是 "year"而 "yyyy"是 "year of era"，因此不明确):

import java.time.*;
import java.time.format.*;
import java.util.*;

public class Test {

    public static void main(String[] args) {
        String dateFormat = "HH:mm:ss MM/dd/uuuu";
        String dateString = "11:30:59 02/31/2015";
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter
            .ofPattern(dateFormat, Locale.US)
            .withResolverStyle(ResolverStyle.STRICT);
        try {
            LocalDateTime date = LocalDateTime.parse(dateString, dateTimeFormatter);
            System.out.println(date);
        } catch (DateTimeParseException e) {
            // Throw invalid date message
            System.out.println("Exception was thrown");
        }
    }
}