Java将GMT/UTC转换为本地时间无法正常工作 [英] Java Convert GMT/UTC to Local time doesn't work as expected

问题描述

为了显示可重现的场景，我正在执行以下操作

In Order to show a reproducible scenario, I am doing the following

1. 获取当前系统时间(本地时间)

1. Get the current system time (local time)

将当地时间转换为UTC//在这里工作正常

Convert Local time to UTC // Works Fine Till here

将UTC时间倒回本地时间.遵循了3种不同的方法(下面列出)，但是所有3种方法都只保留UTC时间.

Reverse the UTC time, back to local time. Followed 3 different approaches (listed below) but all the 3 approaches retains the time in UTC only.

{

long ts = System.currentTimeMillis();
Date localTime = new Date(ts);
String format = "yyyy/MM/dd HH:mm:ss";
SimpleDateFormat sdf = new SimpleDateFormat (format);

// Convert Local Time to UTC (Works Fine) 
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
Date gmtTime = new Date(sdf.format(localTime));
System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime());

// Reverse Convert UTC Time to Locale time (Doesn't work) Approach 1
sdf.setTimeZone(TimeZone.getDefault());        
localTime = new Date(sdf.format(gmtTime));
System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime());

// Reverse Convert UTC Time to Locale time (Doesn't work) Approach 2 using DateFormat
DateFormat df = new SimpleDateFormat (format);
df.setTimeZone(TimeZone.getDefault());
localTime = df.parse((df.format(gmtTime)));
System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime());

// Approach 3
Calendar c = new GregorianCalendar(TimeZone.getDefault());
c.setTimeInMillis(gmtTime.getTime());
System.out.println("Local Time " + c.toString());

}

推荐答案

我还建议使用 Joda ，如前所述.

I also recommend using Joda as mentioned before.

只能使用以下标准的 Java Date对象解决问题:

Solving your problem using standard Java Date objects only can be done as follows:

    // **** YOUR CODE **** BEGIN ****
    long ts = System.currentTimeMillis();
    Date localTime = new Date(ts);
    String format = "yyyy/MM/dd HH:mm:ss";
    SimpleDateFormat sdf = new SimpleDateFormat(format);

    // Convert Local Time to UTC (Works Fine)
    sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
    Date gmtTime = new Date(sdf.format(localTime));
    System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:"
            + gmtTime.toString() + "," + gmtTime.getTime());

    // **** YOUR CODE **** END ****

    // Convert UTC to Local Time
    Date fromGmt = new Date(gmtTime.getTime() + TimeZone.getDefault().getOffset(localTime.getTime()));
    System.out.println("UTC time:" + gmtTime.toString() + "," + gmtTime.getTime() + " --> Local:"
            + fromGmt.toString() + "-" + fromGmt.getTime());

输出:

Local:Tue Oct 15 12:19:40 CEST 2013,1381832380522 --> UTC time:Tue Oct 15 10:19:40 CEST 2013,1381825180000
UTC time:Tue Oct 15 10:19:40 CEST 2013,1381825180000 --> Local:Tue Oct 15 12:19:40 CEST 2013-1381832380000

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