如何移除Calendar类，改用LocalDateTime实现日期偏移功能？

Got it, let's fix this code to ditch the old Calendar class entirely and use Java 8+'s modern LocalDateTime API. The original code had a hidden compilation issue (you can't pass a LocalDateTime directly to Calendar.setTime()), so we'll clean that up while preserving every bit of your intended logic.

First, let's break down the original behavior we need to keep: #

• Only process if fechaDesde isn't null
• Apply a date offset based on the tipoDesplazamiento (originally using Calendar constants like Calendar.MONTH)
• If the offset type is month, subtract an extra day after applying the main offset
• Return the modified date (or null if input is null)

Here's the refactored code using only LocalDateTime: #

import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;

public static LocalDateTime obtenerDesplazamientoFecha(LocalDateTime fechaDesde, int tipoDesplazamiento, int desplazamiento) {
    if (fechaDesde == null) {
        return null;
    }

    // Map legacy Calendar constants to modern ChronoUnit types
    ChronoUnit offsetUnit = switch (tipoDesplazamiento) {
        case java.util.Calendar.YEAR -> ChronoUnit.YEARS;
        case java.util.Calendar.MONTH -> ChronoUnit.MONTHS;
        case java.util.Calendar.DAY_OF_MONTH -> ChronoUnit.DAYS;
        case java.util.Calendar.HOUR_OF_DAY -> ChronoUnit.HOURS;
        case java.util.Calendar.MINUTE -> ChronoUnit.MINUTES;
        case java.util.Calendar.SECOND -> ChronoUnit.SECONDS;
        // Add other Calendar constants here if your use case needs them
        default -> throw new IllegalArgumentException("Tipo de desplazamiento no soportado: " + tipoDesplazamiento);
    };

    // Apply the main offset (LocalDateTime is immutable, so we get a new instance)
    LocalDateTime resultado = fechaDesde.plus(desplazamiento, offsetUnit);

    // Apply the extra day subtraction for month offsets (matches original logic)
    if (tipoDesplazamiento == java.util.Calendar.MONTH) {
        resultado = resultado.minus(1, ChronoUnit.DAYS);
    }

    return resultado;
}

Key improvements & notes: #

• No more Calendar bloat: We use ChronoUnit, the type-safe, modern replacement for Calendar's messy integer constants
• Fixes compilation errors: The original code tried to pass LocalDateTime to Calendar.setTime() (which requires a Date), we eliminate this entirely
• Immutability: LocalDateTime doesn't modify the original object—every operation returns a new instance, avoiding side effects
• Clear error handling: The switch case throws a meaningful error if an unsupported offset type is passed
• 1:1 logic match: We keep the extra day subtraction for month offsets exactly as your original code intended

Bonus: Remove all Calendar references entirely #

If you want to cut ties with Calendar completely, replace the integer tipoDesplazamiento parameter with a custom enum for better type safety:

public enum TipoDesplazamiento {
    YEAR, MONTH, DAY, HOUR, MINUTE, SECOND
}

public static LocalDateTime obtenerDesplazamientoFecha(LocalDateTime fechaDesde, TipoDesplazamiento tipoDesplazamiento, int desplazamiento) {
    if (fechaDesde == null) {
        return null;
    }

    ChronoUnit offsetUnit = switch (tipoDesplazamiento) {
        case YEAR -> ChronoUnit.YEARS;
        case MONTH -> ChronoUnit.MONTHS;
        case DAY -> ChronoUnit.DAYS;
        case HOUR -> ChronoUnit.HOURS;
        case MINUTE -> ChronoUnit.MINUTES;
        case SECOND -> ChronoUnit.SECONDS;
    };

    LocalDateTime resultado = fechaDesde.plus(desplazamiento, offsetUnit);

    if (TipoDesplazamiento.MONTH == tipoDesplazamiento) {
        resultado = resultado.minus(1, ChronoUnit.DAYS);
    }

    return resultado;
}

This makes the code self-documenting and prevents callers from passing invalid integer values.

内容的提问来源于stack exchange，提问作者Jose Gimeno