java.text.ParseException : Unparseable date: java. 文本.DateFormat.parse(DateFormat.java:579)

Question

我对 SimpleDateFormat 有疑问。

SimpleDateFormat dtfmt=new SimpleDateFormat("dd MMM yyyy hh:mm a", Locale.getDefault());
Date dt=dtfmt.parse(deptdt);

在 Android Emulator 中工作正常，但在手机中出现此错误:

W/System.err: java.text.ParseException: Unparseable date: "24 Oct 2016 7:31 pm" (at offset 3) W/System.err: at java.text.DateFormat.parse(DateFormat.java:579)

有什么解决办法吗？

Answer 1

切勿在没有Locale的情况下使用SimpleDateFormat 或DateTimeFormatter

由于给定的日期时间是英文的，因此您应该将 Locale.ENGLISH 与您的日期时间解析器一起使用；否则解析将在使用非英语语言环境的系统(计算机、电话等)中失败。

另请注意，java.util 的日期时间 API 及其格式化 API SimpleDateFormat 已过时且容易出错。建议完全停止使用它们并切换到 modern date-time API .

• 出于任何原因，如果您必须坚持使用 Java 6 或 Java 7，您可以使用 ThreeTen-Backport它将大部分 java.time 功能反向移植到 Java 6 和 7。
• 如果您正在为 Android 项目工作并且您的 Android API 级别仍然不符合 Java-8，请检查 Java 8+ APIs available through desugaring和 How to use ThreeTenABP in Android Project .

演示:

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        final String strDateTime = "24 Oct 2016 7:31 pm";
        DateTimeFormatter dtf = new DateTimeFormatterBuilder()
                .parseCaseInsensitive()             // For case-insensitive (e.g. am, Am, AM) parsing 
                .appendPattern("d MMM uuuu h:m a")  // Pattern conforming to the date-time string
                .toFormatter(Locale.ENGLISH);       // Locale
        LocalDateTime ldt = LocalDateTime.parse(strDateTime, dtf);
        System.out.println(ldt);
    }
}

输出:

2016-10-24T19:31

默认情况下，DateTimeFormatter#ofPattern使用 default FORMAT locale JVM 根据主机环境在启动期间设置。 SimpleDateFormat也是如此.我试图通过以下演示来说明问题:

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        final String strDateTime = "24 Oct 2016 7:31 pm";           
        DateTimeFormatter dtfWithDefaultLocale = null;          

        System.out.println("JVM's Locale: " + Locale.getDefault());
        // Using DateTimeFormatter with the default Locale
        dtfWithDefaultLocale = getDateTimeFormatterWithDefaultLocale();
        System.out.println("DateTimeFormatter's Locale: " + dtfWithDefaultLocale.getLocale());
        System.out.println(
                "Parsed with JVM's default locale: " + LocalDateTime.parse(strDateTime, dtfWithDefaultLocale));

        // Setting the JVM's default locale to Locale.FRANCE
        Locale.setDefault(Locale.FRANCE);
        
        // Using DateTimeFormatter with Locale.ENGLISH explicitly (recommended)
        DateTimeFormatter dtfWithEnglishLocale = getDateTimeFormatterWithEnglishLocale();
        System.out.println("JVM's Locale: " + Locale.getDefault());
        System.out.println("DateTimeFormatter's Locale: " + dtfWithEnglishLocale.getLocale());
        LocalDateTime zdt = LocalDateTime.parse(strDateTime, dtfWithEnglishLocale);
        System.out.println("Parsed with Locale.ENGLISH: " + zdt);

        
        System.out.println("JVM's Locale: " + Locale.getDefault());
        // Using DateTimeFormatter with the default Locale
        dtfWithDefaultLocale = getDateTimeFormatterWithDefaultLocale();
        System.out.println("DateTimeFormatter's Locale: " + dtfWithDefaultLocale.getLocale());
        System.out.println(
                "Parsed with JVM's default locale: " + LocalDateTime.parse(strDateTime, dtfWithDefaultLocale));
    }
    
    static DateTimeFormatter getDateTimeFormatterWithDefaultLocale() {
        return new DateTimeFormatterBuilder()
                .parseCaseInsensitive()             
                .appendPattern("d MMM uuuu h:m a") 
                .toFormatter(); // Using default Locale
    }
    
    static DateTimeFormatter getDateTimeFormatterWithEnglishLocale() {
        return new DateTimeFormatterBuilder()
                .parseCaseInsensitive()             
                .appendPattern("d MMM uuuu h:m a") 
                .toFormatter(Locale.ENGLISH); // Using Locale.ENGLISH
    }
}

输出:

JVM's Locale: en_GB
DateTimeFormatter's Locale: en_GB
Parsed with JVM's default locale: 2016-10-24T19:31
JVM's Locale: fr_FR
DateTimeFormatter's Locale: en
Parsed with Locale.ENGLISH: 2016-10-24T19:31
JVM's Locale: fr_FR
DateTimeFormatter's Locale: fr_FR
Exception in thread "main" java.time.format.DateTimeParseException: Text '24 Oct 2016 7:31 pm' could not be parsed at index 3
    at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2046)
    at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1948)
    at java.base/java.time.LocalDateTime.parse(LocalDateTime.java:492)
    at Main.main(Main.java:34)

---

以下演示，使用SimpleDateFormat，只是为了完整起见:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

public class Main {
    public static void main(String[] args) throws ParseException {
        final String strDateTime = "24 Oct 2016 7:31 pm";
        SimpleDateFormat sdf = new SimpleDateFormat("d MMM yyyy h:m a", Locale.ENGLISH);
        Date date = sdf.parse(strDateTime);
        System.out.println(date);
    }
}

输出:

Mon Oct 24 19:31:00 BST 2016