技术求助：回历与公历互转、日期计算及时间段判定方案

Hey there! I see you've spent over 10 hours hunting for solutions to these date-related tasks, and you're hitting snags with HijrahDate and Joda Date. Let's fix that using Java's modern java.time APIs—HijrahDate is part of this built-in library, and it's the recommended replacement for Joda (especially if you're on Java 8+). Here's how to tackle each of your three requirements step by step:

This is straightforward with HijrahDate—no external dependencies needed. Here's how to convert both ways:

Convert Hijri to Gregorian #

import java.time.LocalDate;
import java.time.chrono.HijrahDate;
import java.time.temporal.ChronoField;

// Example: Create a specific Hijri date (1445/01/01)
HijrahDate hijriDate = HijrahDate.now()
    .with(ChronoField.YEAR, 1445)
    .with(ChronoField.MONTH_OF_YEAR, 1)
    .with(ChronoField.DAY_OF_MONTH, 1);

// Convert to Gregorian calendar (LocalDate)
LocalDate gregorianDate = LocalDate.from(hijriDate);
System.out.println("Hijri 1445-01-01 → Gregorian: " + gregorianDate);

Convert Gregorian to Hijri #

import java.time.LocalDate;
import java.time.chrono.HijrahDate;
import java.time.temporal.ChronoField;

// Example: Create a specific Gregorian date (2023-07-19)
LocalDate gregorianDate = LocalDate.of(2023, 7, 19);

// Convert to Hijri calendar
HijrahDate hijriDate = HijrahDate.from(gregorianDate);
int hijriYear = hijriDate.get(ChronoField.YEAR);
int hijriMonth = hijriDate.get(ChronoField.MONTH_OF_YEAR);
int hijriDay = hijriDate.get(ChronoField.DAY_OF_MONTH);
System.out.println("Gregorian 2023-07-19 → Hijri: " + hijriYear + "-" + hijriMonth + "-" + hijriDay);

Use ChronoUnit.DAYS to get the signed difference between any two dates (works for both Gregorian and Hijri dates, since they implement the Temporal interface):

import java.time.LocalDate;
import java.time.chrono.HijrahDate;
import java.time.temporal.ChronoUnit;

// Current Gregorian date
LocalDate currentGregorian = LocalDate.now();
// Target Gregorian date (e.g., 2024-01-01)
LocalDate targetGregorian = LocalDate.of(2024, 1, 1);

// Calculate days between (positive = future, negative = past)
long daysToTarget = ChronoUnit.DAYS.between(currentGregorian, targetGregorian);
System.out.println("Days until 2024-01-01: " + daysToTarget);

// For Hijri dates, same logic applies:
HijrahDate currentHijri = HijrahDate.now();
HijrahDate targetHijri = HijrahDate.from(targetGregorian);
long hijriDaysToTarget = ChronoUnit.DAYS.between(currentHijri, targetHijri);
System.out.println("Days until Hijri target date: " + hijriDaysToTarget);

Let's use your example: checking if the current date is within 5 days before or after the start of Muharram (the first month of the Hijri calendar):

import java.time.chrono.HijrahDate;
import java.time.temporal.ChronoField;
import java.time.temporal.TemporalAdjusters;

// Get current Hijri date
HijrahDate currentHijri = HijrahDate.now();

// Get the first day of Muharram in the current Hijri year
HijrahDate muharramFirstDay = currentHijri
    .with(ChronoField.MONTH_OF_YEAR, 1) // Muharram is month 1
    .with(TemporalAdjusters.firstDayOfMonth());

// Define the range: 5 days before to 5 days after Muharram's start
HijrahDate rangeStart = muharramFirstDay.minusDays(5);
HijrahDate rangeEnd = muharramFirstDay.plusDays(5);

// Check if current date is within the range
boolean isInMuharramWindow = !currentHijri.isBefore(rangeStart) && !currentHijri.isAfter(rangeEnd);
System.out.println("Is current date in Muharram ±5 days? " + isInMuharramWindow);

A quick note: If you're stuck on Java 7 or earlier, Joda Time is an option, but java.time is way more robust and integrated with modern Java. The HijrahDate class uses the Umm al-Qura calendar, which is the standard for most Islamic countries.

内容的提问来源于stack exchange，提问作者Visonge