应用需支持公历、波斯历、伊斯兰历切换，求方案及Joda Time可行性

Hey there! Great question—let's break this down step by step to get you sorted.

Absolutely, but with one small caveat: the core Joda Time library only ships with Gregorian/ISO calendar support out of the box. However, there are well-maintained third-party extensions that add full support for Jalali (Persian) and Hijiri (Islamic) calendars, which integrate seamlessly with the core library. This makes Joda Time a solid choice for your multi-calendar requirements.

1. Add Dependencies #

First, include the core Joda Time library and the required calendar extensions in your project. Here's how to do it for Maven:

<!-- Core Joda Time -->
<dependency>
    <groupId>joda-time</groupId>
    <artifactId>joda-time</artifactId>
    <version>2.12.5</version>
</dependency>
<!-- Jalali Calendar Extension -->
<dependency>
    <groupId>com.github.mfathi91</groupId>
    <artifactId>joda-time-jalali</artifactId>
    <version>2.12.5</version>
</dependency>
<!-- Hijiri Calendar Extension -->
<dependency>
    <groupId>org.joda</groupId>
    <artifactId>joda-time-hijri</artifactId>
    <version>1.0.1</version>
</dependency>

For Gradle, adjust to use implementation instead of <dependency> blocks, matching the versions above to avoid compatibility issues.

2. Build a Global Date State Manager #

The key to seamless calendar switching is to store a calendar-agnostic timestamp as your single source of truth, instead of tying your app to any one calendar's date object. Joda's Instant class is perfect for this—it represents a point in time independent of any calendar system.

Here's a simplified singleton manager to handle global date state and calendar switching:

import org.joda.time.Instant;
import org.joda.time.DateTime;
import org.joda.time.DateTimeZone;
import com.github.mfathi91.jdt.JalaliDateTime;
import org.joda.time.hijri.HijriDateTime;

public enum CalendarType { GREGORIAN, JALALI, HIJIRI }

public class CalendarManager {
    private static final CalendarManager INSTANCE = new CalendarManager();
    private Instant currentInstant;
    private DateTimeZone timeZone = DateTimeZone.getDefault();
    private CalendarType activeCalendar = CalendarType.GREGORIAN;

    private CalendarManager() {
        // Initialize with current time
        currentInstant = Instant.now();
    }

    public static CalendarManager getInstance() {
        return INSTANCE;
    }

    // Switch to a different calendar type
    public void switchCalendar(CalendarType newType) {
        this.activeCalendar = newType;
        notifyDateUpdated(); // Trigger UI updates across the app
    }

    // Get the date formatted for the active calendar
    public DateTime getActiveCalendarDate() {
        switch (activeCalendar) {
            case GREGORIAN:
                return new DateTime(currentInstant, timeZone);
            case JALALI:
                return new JalaliDateTime(currentInstant, timeZone);
            case HIJIRI:
                return new HijriDateTime(currentInstant, timeZone);
            default:
                return new DateTime(currentInstant, timeZone);
        }
    }

    // Update the global date (called when user selects a new date in the picker)
    public void updateDate(DateTime selectedDate) {
        // Convert any calendar's date to an Instant for universal storage
        this.currentInstant = selectedDate.toInstant();
        notifyDateUpdated();
    }

    // Notify all registered components that the date/calendar has changed
    private void notifyDateUpdated() {
        // Implement this with your app's architecture:
        // - Use LiveData for Android
        // - RxJava Observables for reactive apps
        // - Custom listener interfaces for simpler setups
    }
}

3. Integrate the Date Picker & Sync Components #

• Picker Initialization: When your date picker loads, fetch the active calendar's date via CalendarManager.getInstance().getActiveCalendarDate() and render it accordingly.
• Date Selection: When the user picks a new date, pass the selected DateTime (from the active calendar) to CalendarManager.getInstance().updateDate(selectedDate). The manager converts it to an Instant and triggers updates.
• Calendar Switch: Add a toggle/setting for users to switch calendar types. When triggered, call CalendarManager.getInstance().switchCalendar(newType). All components listening for date updates will automatically fetch the new calendar's date and refresh their UI.

4. Handle Calendar Conversions Automatically #

Since all date storage uses Instant, conversions between calendars are handled entirely by the Joda extensions. For example:

• If a user selects a Gregorian date, it's stored as an Instant. When switching to Jalali, JalaliDateTime will automatically calculate the correct Persian date from that timestamp.
• No manual date math is needed—extensions like joda-time-jalali and joda-time-hijri handle all the complex calendar rules for you.

• If you're building for Android, consider ThreeTenABP (an Android-compatible port of Java 8's Time API) instead of Joda Time, as Joda Time is no longer actively maintained. ThreeTenABP also has extensions for Jalali and Hijiri calendars, following a similar pattern to the above.
• Ensure all extension versions match the core library version to avoid runtime errors.
• Use your app's existing architecture (MVVM, MVP, etc.) to implement the notifyDateUpdated logic—this ensures clean, maintainable sync across all date-related components.

内容的提问来源于stack exchange，提问作者Pejman Gh