java.util.Date 格式转换 yyyy-mm-dd 到 mm-dd-yyyy [英] java.util.Date format conversion yyyy-mm-dd to mm-dd-yyyy

问题描述

我有一个 java.util.Date，格式为 yyyy-mm-dd.我希望它的格式为 mm-dd-yyyy

I have a java.util.Date in the format yyyy-mm-dd. I want it to be in the format mm-dd-yyyy

以下是我为此转换尝试的示例实用程序:

Below is the sample util I tried out for this conversion:

// Setting the pattern
SimpleDateFormat sm = new SimpleDateFormat("mm-dd-yyyy");
// myDate is the java.util.Date in yyyy-mm-dd format
// Converting it into String using formatter
String strDate = sm.format(myDate);
//Converting the String back to java.util.Date
Date dt = sm.parse(strDate);

我得到的输出仍然不是 mm-dd-yyyy 格式.

Still the output I am getting is not in the format mm-dd-yyyy.

请告诉我如何将 java.util.Date 从 yyyy-mm-dd 格式化为 mm-dd-yyyy

Kindly let me know how to format a java.util.Date from yyyy-mm-dd to mm-dd-yyyy

推荐答案

Date 是自 Unix 纪元(1970 年 1 月 1 日 00:00:00 UTC)以来毫秒数的容器.

Date is a container for the number of milliseconds since the Unix epoch ( 00:00:00 UTC on 1 January 1970).

它没有格式的概念.

LocalDateTime ldt = LocalDateTime.now();
System.out.println(DateTimeFormatter.ofPattern("MM-dd-yyyy", Locale.ENGLISH).format(ldt));
System.out.println(DateTimeFormatter.ofPattern("yyyy-MM-dd", Locale.ENGLISH).format(ldt));
System.out.println(ldt);

输出...

05-11-2018
2018-05-11
2018-05-11T17:24:42.980

Java 7-

您应该使用 ThreeTen Backport

例如...

Date myDate = new Date();
System.out.println(myDate);
System.out.println(new SimpleDateFormat("MM-dd-yyyy").format(myDate));
System.out.println(new SimpleDateFormat("yyyy-MM-dd").format(myDate));
System.out.println(myDate);

输出...

Wed Aug 28 16:20:39 EST 2013
08-28-2013
2013-08-28
Wed Aug 28 16:20:39 EST 2013

没有任何格式改变了基础 Date 值.这就是 DateFormatters

None of the formatting has changed the underlying Date value. This is the purpose of the DateFormatters

更新了其他示例

以防万一第一个例子没有意义...

Just in case the first example didn't make sense...

此示例使用两个格式化程序来格式化相同的日期.然后我使用这些相同的格式化程序将 String 值解析回 Dates.生成的解析不会改变 Date 报告其值的方式.

This example uses two formatters to format the same date. I then use these same formatters to parse the String values back to Dates. The resulting parse does not alter the way Date reports it's value.

Date#toString 只是其内容的转储.您无法更改此设置，但您可以按照您喜欢的任何方式设置 Date 对象的格式

Date#toString is just a dump of it's contents. You can't change this, but you can format the Date object any way you like

try {
    Date myDate = new Date();
    System.out.println(myDate);

    SimpleDateFormat mdyFormat = new SimpleDateFormat("MM-dd-yyyy");
    SimpleDateFormat dmyFormat = new SimpleDateFormat("yyyy-MM-dd");

    // Format the date to Strings
    String mdy = mdyFormat.format(myDate);
    String dmy = dmyFormat.format(myDate);

    // Results...
    System.out.println(mdy);
    System.out.println(dmy);
    // Parse the Strings back to dates
    // Note, the formats don't "stick" with the Date value
    System.out.println(mdyFormat.parse(mdy));
    System.out.println(dmyFormat.parse(dmy));
} catch (ParseException exp) {
    exp.printStackTrace();
}

哪些输出...

Wed Aug 28 16:24:54 EST 2013
08-28-2013
2013-08-28
Wed Aug 28 00:00:00 EST 2013
Wed Aug 28 00:00:00 EST 2013

此外，请注意格式模式.仔细看看 SimpleDateFormat 以确保您没有使用错误的模式 ;)

Also, be careful of the format patterns. Take a closer look at SimpleDateFormat to make sure you're not using the wrong patterns ;)

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