java - 时区转换期间的奇怪行为

Question

我正在尝试将以 EST 时区打印的日期转换为以 GMT/UTC 打印的日期

package com.stefano;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;


public class MainEntry {

/**
 * @param args
 * @throws ParseException 
 */


public static void main(String[] args) throws ParseException {


    String dateTime = "1307011200"; //12:00PM 01 July 2013
    System.out.println("Input -> " + dateTime);
    SimpleDateFormat format = new SimpleDateFormat("yyMMddHHmm");
    format.setTimeZone(TimeZone.getTimeZone("EST"));
    Date date = format.parse(dateTime);
    System.out.println("Intermediate -> " + date);
    format.setTimeZone(TimeZone.getTimeZone("GMT"));
    System.out.println("Output -> " + format.format(date));


    }

}

它给出的输出是:

Input -> 1307011200
Intermediate -> Mon Jul 01 17:00:00 BST 2013
Output -> 1307011600

尽管 EST 和 GMT 之间的时差始终为 5，但不知何故与 BST 有所牵连。

我不能使用 Joda-Time .

Answer 1

SimpleDateFormat.parse(String) 方法的 javadoc 引用了 parse(String, ParsePosition) 方法，它说:

This parsing operation uses the calendar to produce a Date. As a result, the calendar's date-time fields and the TimeZone value may have been overwritten, depending on subclass implementations. Any TimeZone value that has previously been set by a call to setTimeZone may need to be restored for further operations.

据此，您不能使用此方法来告诉 SimpleDateFormat 哪个时区给定的日期是在。您可以像这样修复此方法:

String dateTime = "1307011200"; // 12:00PM 01 July 2013
dateTime += " EST"; // append the timezone information to the input string
System.out.println("Input -> " + dateTime);
SimpleDateFormat format = new SimpleDateFormat("yyMMddHHmm z"); // tell the formatter to look for the timezone info
Date date = format.parse(dateTime);
System.out.println("Intermediate -> " + date);
format.setTimeZone(TimeZone.getTimeZone("GMT"));
System.out.println("Output -> " + format.format(date));

这也将使用您本地的时区打印 Date 对象，但它展示了一种使用给定时区解析 dateTime 字符串的方法。