问题描述

如何将日历日期转换为yyyy-MM-dd格式.

How to convert calendar date to yyyy-MM-dd format.

Calendar cal = Calendar.getInstance();
cal.add(Calendar.DATE, 1);
Date date = cal.getTime();             
SimpleDateFormat format1 = new SimpleDateFormat("yyyy-MM-dd");
String date1 = format1.format(date);            
Date inActiveDate = null;
try {
    inActiveDate = format1.parse(date1);
} catch (ParseException e1) {
    // TODO Auto-generated catch block
    e1.printStackTrace();
}

这将产生 inActiveDate = Wed Sep 26 00:00:00 IST 2012.但我需要的是2012-09-26.我的目的是使用 Hibernate 标准将此日期与我的数据库中的另一个日期进行比较.所以我需要 yyyy-MM-dd 格式的日期对象.

This will produce inActiveDate = Wed Sep 26 00:00:00 IST 2012. But what I need is 2012-09-26. My purpose is to compare this date with another date in my database using Hibernate criteria. So I need the date object in yyyy-MM-dd format.

推荐答案

Java Date 是自 1970 年 1 月 1 日 00:00:00 GMT 以来的毫秒数的容器.

A Java Date is a container for the number of milliseconds since January 1, 1970, 00:00:00 GMT.

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当你使用 System.out.println(date) 之类的东西时，Java 使用 Date.toString() 来打印内容.

When you use something like System.out.println(date), Java uses Date.toString() to print the contents.

更改它的唯一方法是覆盖 Date 并提供您自己的 Date.toString() 实现.现在在你启动你的 IDE 并尝试这个之前，我不会；它只会使事情复杂化.您最好将日期格式化为您想要使用(或显示)的格式.

The only way to change it is to override Date and provide your own implementation of Date.toString(). Now before you fire up your IDE and try this, I wouldn't; it will only complicate matters. You are better off formatting the date to the format you want to use (or display).

LocalDateTime ldt = LocalDateTime.now().plusDays(1);
DateTimeFormatter formmat1 = DateTimeFormatter.ofPattern("yyyy-MM-dd", Locale.ENGLISH);
System.out.println(ldt);
// Output "2018-05-12T17:21:53.658"

String formatter = formmat1.format(ldt);
System.out.println(formatter);
// 2018-05-12

Java 8 之前的版本

您应该使用 ThreeTen Backport

出于历史目的保留以下内容(作为原始答案)

The following is maintained for historical purposes (as the original answer)

你可以做的是格式化日期.

What you can do, is format the date.

Calendar cal = Calendar.getInstance();
cal.add(Calendar.DATE, 1);
SimpleDateFormat format1 = new SimpleDateFormat("yyyy-MM-dd");
System.out.println(cal.getTime());
// Output "Wed Sep 26 14:23:28 EST 2012"

String formatted = format1.format(cal.getTime());
System.out.println(formatted);
// Output "2012-09-26"

System.out.println(format1.parse(formatted));
// Output "Wed Sep 26 00:00:00 EST 2012"

这些实际上是相同的日期，表示方式不同.

These are actually the same date, represented differently.

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