使用时区将字符串转换为日期

Question

I have a string in the pattern yyyy-MM-dd hh:mm a and i can get the time zone object separately in which the above string represents the date.

I want to convert this to the below format. yyyy-MM-dd HH:mm:ss Z

How can i do this?

Answer 1

You can use SimpleDateFormat with yyyy-MM-dd HH:mm:ss and explicitly set the TimeZone :

public static Date getSomeDate(final String str, final TimeZone tz)
    throws ParseException {
  final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm a");
  sdf.setTimeZone(tz);
  return sdf.parse(str);
}

/**
 * @param args
 * @throws IOException
 * @throws InterruptedException
 * @throws ParseException
 */
public static void main(final String[] args) throws ParseException {
  final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
  System.out.println(sdf.format(getSomeDate(
      "2010-11-17 01:12 pm", TimeZone.getTimeZone("Europe/Berlin"))));
  System.out.println(sdf.format(getSomeDate(
      "2010-11-17 01:12 pm", TimeZone.getTimeZone("America/Chicago"))));
}

Prints out:

2010-11-17 13:12:00 +0100

2010-11-17 20:12:00 +0100

Update 2010-12-01: If you want to explicitly printout a special TimeZone, set it in the SimpleDateFormat:

sdf.setTimeZone(TimeZone .getTimeZone("IST")); 
System.out.println(sdf.format(getSomeDate(
    "2010-11-17 01:12 pm", TimeZone.getTimeZone("IST"))));

Which prints 2010-11-17 13:12:00 +0530

Answer 2

tl;dr

LocalDateTime.parse(                        // Parse string as value without time zone and without offset-from-UTC.
    "2017-01-23 12:34 PM" , 
    DateTimeFormatter.ofPattern( "uuuu-MM-dd hh:mm a" )
)                                           // Returns a `LocalDateTime` object.
.atZone( ZoneId.of( "America/Montreal" ) )  // Assign time zone, to determine a moment. Returns a `ZonedDateTime` object.
.toInstant()                                // Adjusts from zone to UTC.
.toString()                                 // Generate string: 2017-01-23T17:34:00Z
.replace( "T" , " " )                       // Substitute SPACE for 'T' in middle.
.replace( "Z" , " Z" )                      // Insert SPACE before 'Z'.

Avoid legacy date-time classes

The other Answers use the troublesome old date-time classes ( Date , Calendar , etc.), now legacy, supplanted by the java.time classes.

LocalDateTime

I have a string in the pattern yyyy-MM-dd hh:mm a

Such an input string lacks any indication of offset-from-UTC or time zone. So we parse as a LocalDateTime .

Define a formatting pattern to match your input with a DateTimeFormatter object.

String input = "2017-01-23 12:34 PM" ;
DateTimeFormatter f = DateTimeFormatter.ofPattern( "uuuu-MM-dd hh:mm a" );
LocalDateTime ldt = LocalDateTime.parse( input , f );

ldt.toString(): 2017-01-23T12:34

Note that a LocalDateTime is not a specific moment, only a vague idea about a range of possible moments. For example, a few minutes after midnight in Paris France is still “yesterday” in Montréal Canada. So without the context of a time zone such as Europe/Paris or America/Montreal , just saying “a few minutes after midnight” has no meaning.

ZoneId

and i can get the time zone object separately in which the above string represents the date.

A time zone is represented by the ZoneId class.

Specify a proper time zone name in the format of continent/region , such as America/Montreal , Africa/Casablanca , or Pacific/Auckland . Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

ZoneId z = ZoneId.of( "America/Montreal" );

ZonedDateTime

Apply the ZoneId to get a ZonedDateTime which is indeed a point on the timeline, a specific moment in history.

ZonedDateTime zdt = ldt.atZone( z );

zdt.toString(): 2017-01-23T12:34-05:00[America/Montreal]

Instant

I want to convert this to the below format. yyyy-MM-dd HH:mm:ss Z

First, know that a Z literal character is short for Zulu and means UTC . In other words, an offset-from-UTC of zero hours, +00:00 .

The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).

You can extract a Instant object from a ZonedDateTime .

Instant instant = zdt.toInstant();  // Extracting the same moment but in UTC.

To generate a string in standard ISO 8601 format, such as 2017-01-22T18:21:13.354Z , call toString . The standard format has no spaces, uses a T to separate the year-month-date from the hour-minute-second, and appends the Z canonically for an offset of zero.

String output = instant.toString();

instant.toString(): 2017-01-23T17:34:00Z

I strongly suggest using the standard formats whenever possible. If you insist on using spaces as in your stated desired format, either define your own formatting pattern in a DateTimeFormatter object or just do a string manipulation on the output of Instant::toString .

String output = instant.toString()
                       .replace( "T" , " " )  // Substitute SPACE for T.
                       .replace( "Z" , " Z" ); // Insert SPACE before Z.

output: 2017-01-23 17:34:00 Z

Try this code live at IdeOne.com .

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

Where to obtain the java.time classes?

• Java SE 8 and SE 9 and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use ThreeTenABP… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .

Answer 3

Use SimpleDateFormat

String string1 = "2009-10-10 12:12:12 ";
SimpleDateFormat sdf =  new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z")
sdf.setTimeZone(tz);
Date date = sdf.parse(string1);

Answer 4

Undoubtedly, the format which is generally used will be of a form 2014-10-05T15:23:01Z (TZ)

For that one has to use this code

SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
String dateInString = "2014-10-05T15:23:01Z";

 try {

     Date date = formatter.parse(dateInString.replaceAll("Z$", "+0000"));
     System.out.println(date);

 } catch (ParseException e) {
     e.printStackTrace();
 }

Its output will be Sun Oct 05 20:53:01 IST 2014

However, I am not sure why we had to replaceAll "Z" if you do not add replaceAll the program will fail.

Answer 5

Create a new instance of SimpleDateFormat using your date pattern. Afterwards you can call it's parse method to convert date strings to a java.util.Date object.