Convert String to java.util.Date_问答_开发者_运维开发者技术经验分享

I am storing the dates in a SQLite database in this format:

d-MMM-yyyy,HH:mm:ss aaa

When I retrieve the date with that format I am get every thing fine except the hour. The hour is always 00. Here is my output:

String date--->29-Apr-2010,13:00:14 PM
After convrting Date--->1272479414000--Thu Apr 29 00:00:14 GMT+05:30 2010

Here is the code:

    Date lScheduledDate = CalendarObj.getTime();
    DateFormat formatter = new SimpleDateFormat("d-MMM-yyyy,HH:mm:ss aaa");
    SomeClassObj.setTime(formatter.format(lScheduledDate));

    String lNextDate = SomeClassObj.getTime();
    DateFormat lFormatter = new SimpleDateFormat("d-MMM-yyyy,HH:mm:ss aaa");
    Date lNextDate = (Date)lFormatter.parse(lNextDate);
    System.out.println("output here"+lN开发者_开发技巧extDate);

What am I doing wrong?

I think your date format does not make sense. There is no 13:00 PM. Remove the "aaa" at the end of your format or turn the HH into hh.

Nevertheless, this works fine for me:

String testDate = "29-Apr-2010,13:00:14 PM";
DateFormat formatter = new SimpleDateFormat("d-MMM-yyyy,HH:mm:ss aaa");
Date date = formatter.parse(testDate);
System.out.println(date);

It prints "Thu Apr 29 13:00:14 CEST 2010".

It sounds like you may want to use something like SimpleDateFormat. http://java.sun.com/j2se/1.4.2/docs/api/java/text/SimpleDateFormat.html

You declare your date format and then call the parse method with your string.

private static final DateFormat DF = new SimpleDateFormat(...);
Date myDate = DF.parse("1234");

And as Guillaume says, set the timezone!

You should set a TimeZone in your DateFormat, otherwise it will use the default one (depending on the settings of the computer).

java.time

While in 2010, java.util.Date was the class we all used (toghether with DateFormat and Calendar), those classes were always poorly designed and are now long outdated. Today one would use java.time, the modern Java date and time API.

        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d-MMM-yyyy,HH:mm:ss");

        String dateTimeStringFromSqlite = "29-Apr-2010,13:00:14";
        LocalDateTime dateTime = LocalDateTime.parse(dateTimeStringFromSqlite, formatter);
        System.out.println("output here: " + dateTime);

Output is:

output here: 2010-04-29T13:00:14

What went wrong in your code?

The combination of uppercase HH and aaa in your format pattern strings does not make much sense since HH is for hour of day, rendering the AM/PM marker from aaa superfluous. It should not do any harm, though, and I have been unable to reproduce the exact results you reported. In any case, your comment is to the point no matter if one uses the old-fashioned SimpleDateFormat or the modern DateTimeFormatter:

'aaa' should not be used, if you use 'aaa' then specify 'hh'

Lowercase hh is for hour within AM or PM, from 01 through 12, so would require an AM/PM marker.

Other tips

In your database, since I understand that SQLite hasn’t got a built-in datetime type, use the standard ISO 8601 format and store time in UTC, for example 2010-04-29T07:30:14Z (the modern Instant class parses and formats such strings as its default, that is, without any explicit formatter).
Don’t use an offset such as GMT+05:30 for time zone. Prefer a real time zone, for example Asia/Colombo, Asia/Kolkata or America/New_York.
If you wanted to use the outdated DateFormat, its parse method returns a Date, so you don’t need the cast in Date lNextDate = (Date)lFormatter.parse(lNextDate);.

Question: Can I use java.time on Android?

Yes, java.time works nicely on older and newer Android devices. It just requires at least Java 6.

In Java 8 and later and on newer Android devices (from API level 26) the modern API comes built-in.
In Java 6 and 7 get the ThreeTen Backport, the backport of the modern classes (ThreeTen for JSR 310; see the links at the bottom).
On (older) Android use the Android edition of ThreeTen Backport. It’s called ThreeTenABP. And make sure you import the date and time classes from org.threeten.bp with subpackages.