工具类：字符串(String)、日期(Date)、日历(Calendar)互相转换，日期获取年月日时分秒

• • 一、来由
  • 二、说明
  • 三、实现
  • 四、测试
  • 五、测试结果
  • 六、注意

每次遇到时间转换问题，总要去翻一翻浏览器，虽然很简单，但就是记不住，于是抽时间自己写了一个比较常用的时间转换工具类，以后直接copy过来用，以后有空再补充一些新的内容。

所有方法实现中的参数，都做了非空校验

package com.example.bean;

import org.springframework.util.StringUtils;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;


public class DateCovertUtil {

    private DateCovertUtil(){};

    
    public static String dateToString(Date date){
        if (date == null){
            throw new RuntimeException("date参数为空");
        }
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        return sdf.format(date);
    }

    
    public static String dateToStringCustomizing(Date date,String formatString){
        if (date == null || StringUtils.isEmpty(formatString)){
            throw new RuntimeException("参数为空,参数date："+date+"  formatString:"+formatString);
        }
        try {
            SimpleDateFormat sdf = new SimpleDateFormat(formatString);
            return sdf.format(date);
        }catch (Exception e){
            throw new RuntimeException("日期格式化设置错误："+formatString);
        }
    }

    
    public static Date stringToDate(String dateStr) {
        if (StringUtils.isEmpty(dateStr)){
            throw new RuntimeException("日期字符串为空");
        }
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date;
        try {
            date = sdf.parse(dateStr);
        }catch (ParseException e){
            throw new RuntimeException("字符串转日期异常,字符串："+dateStr);
        }
        return date;
    }

    
    public static Date stringToDateCustomizing(String dateStr,String formatString) {
        if (StringUtils.isEmpty(dateStr) || StringUtils.isEmpty(formatString)){
            throw new RuntimeException("参数为空，dateStr:"+dateStr+" formatString:"+formatString);
        }
        SimpleDateFormat sdf = new SimpleDateFormat(formatString);
        Date date;
        try {
            date = sdf.parse(dateStr);
        }catch (ParseException e){
            throw new RuntimeException("自定义字符串转日期异常,字符串："+dateStr+" 日期格式:"+formatString);
        }
        return date;
    }

    
    public static Calendar dateToCalendar(Date date) {
        if (date == null){
            throw new RuntimeException("date参数为空");
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        return calendar;
    }

    
    public static Date calendarToDate(Calendar calendar) {
        if (calendar == null){
            throw new RuntimeException("calendar参数为空");
        }
        return calendar.getTime();
    }

    
    public static String calendarToString(Calendar calendar) {
        return dateToString(calendarToDate(calendar));
    }

    
    public static Calendar StringToCalendar(String dateString) {
        return dateToCalendar(stringToDate(dateString));
    }

    
    public static Map dateGetDetail(Date date){
        Map map = new HashMap<>();
        if (date == null){
            throw new RuntimeException("date参数为空");
        }
        Calendar calendar = dateToCalendar(date);
        if (calendar.get(Calendar.YEAR) != 0) { map.put("year", calendar.get(Calendar.YEAR)); }
        if (calendar.get(Calendar.MONTH) != 0) { map.put("month",calendar.get(Calendar.MONTH)+1); }
        if (calendar.get(Calendar.DATE) != 0) { map.put("day",calendar.get(Calendar.DATE)); }
        //12小时制
        if (calendar.get(Calendar.HOUR) != 0) { map.put("hour",calendar.get(Calendar.HOUR)); }
        if (calendar.get(Calendar.MINUTE) != 0) { map.put("minute",calendar.get(Calendar.MINUTE)); }
        if (calendar.get(Calendar.SECOND) != 0) { map.put("second",calendar.get(Calendar.SECOND)); }
        //24小时制
        if (calendar.get(Calendar.HOUR_OF_DAY) != 0) { map.put("hourOfDay",calendar.get(Calendar.HOUR_OF_DAY)); }
        //一周的第几天
        if (calendar.get(Calendar.DAY_OF_WEEK) != 0) { map.put("dayOfWeek",calendar.get(Calendar.DAY_OF_WEEK)); }
        return map;
    }

	
    public static long getCurrentTimeMillis(){
        return System.currentTimeMillis();
    }
}

package com.example.bean;

import java.util.Calendar;
import java.util.Date;
import java.util.Map;

public class Test {
    public static void main(String[] args) {

        //参数准备
        Date date = new Date();
        Calendar calendar = Calendar.getInstance();
        String dateStr = "2021-10-11 20:19:37";

        //Date类型转String类型
        String string1 = DateCovertUtil.dateToString(date);
        System.out.println("Date类型转String类型:n" + string1);

        //Date类型转String类型,自定义转换格式
        String string2 = DateCovertUtil.dateToStringCustomizing(date, "yyyy-MM-dd");
        System.out.println("nDate类型转String类型,自定义转换格式:n" + string2);

        //String类型转Date类型
        Date date1 = DateCovertUtil.stringToDate(dateStr);
        System.out.println("nString类型转Date类型:n"+date1);

        //String类型转Date类型,自定义转换格式
        Date date2 = DateCovertUtil.stringToDateCustomizing(dateStr, "yyyy-MM-dd");
        System.out.println("nString类型转Date类型,自定义转换格式:n" + date2);

        //Date类型转Calendar类型
        Calendar calendar1 = DateCovertUtil.dateToCalendar(date);
        System.out.println("nDate类型转Calendar类型:n" + calendar1);

        //Calendar类型转Date类型
        Date date3 = DateCovertUtil.calendarToDate(calendar);
        System.out.println("nCalendar类型转Date类型:n" + date3);

        //Date类型获取年月日时分秒
        Map dateMap = DateCovertUtil.dateGetDetail(date);
        System.out.println("nDate类型获取年月日时分秒:n" + dateMap);

    }

}

阿里规范中要求代码禁用 static 修饰 SimpleDateFormat，因为SimpleDateFormat是线程不安全的，所以涉及到了多线程可以使用DateTimeFormatter
具体请参考链接: https://blog.csdn.net/afreon/article/details/111878486