如何将日期字符串转换为日期或日历对象？

Question

I have a String representation of a date that I need to create a Date or Calendar object from. I've looked through Date and Calendar APIs but haven't found anything that can do this other than creating my own ugly parse method. I know there must be a way, does anyone know of a solution?

Answer 1

In brief:

DateFormat formatter = new SimpleDateFormat("MM/dd/yy");
try {
  Date date = formatter.parse("01/29/02");
} catch (ParseException e) {
  e.printStackTrace();
}

See SimpleDateFormat javadoc for more.

And to turn it into a Calendar , do:

Calendar calendar = Calendar.getInstance();
calendar.setTime(date);

Answer 2

tl;dr

LocalDate.parse( "2015-01-02" )

java.time

Java 8 and later has a new java.time framework that makes these other answers outmoded. This framework is inspired by Joda-Time , defined by JSR 310 , and extended by the ThreeTen-Extra project. See the Tutorial .

The old bundled classes, java.util.Date/.Calendar, are notoriously troublesome and confusing. Avoid them.

LocalDate

Like Joda-Time, java.time has a class LocalDate to represent a date-only value without time-of-day and without time zone.

ISO 8601

If your input string is in the standard ISO 8601 format of yyyy-MM-dd , you can ask that class to directly parse the string with no need to specify a formatter.

The ISO 8601 formats are used by default in java.time, for both parsing and generating string representations of date-time values.

LocalDate localDate = LocalDate.parse( "2015-01-02" );

Formatter

If you have a different format, specify a formatter from the java.time.format package. You can either specify your own formatting pattern or let java.time automatically localize as appropriate to a Locale specifying a human language for translation and cultural norms for deciding issues such as period versus comma.

Formatting pattern

Read the DateTimeFormatter class doc for details on the codes used in the format pattern. They vary a bit from the old outmoded java.text.SimpleDateFormat class patterns.

Note how the second argument to the parse method is a method reference , syntax added to Java 8 and later.

String input = "January 2, 2015";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern ( "MMMM d, yyyy" , Locale.US );
LocalDate localDate = LocalDate.parse ( input , formatter );

Dump to console.

System.out.println ( "localDate: " + localDate );

localDate: 2015-01-02

Localize automatically

Or rather than specify a formatting pattern, let java.time localize for you. Call DateTimeFormatter.ofLocalizedDate , and be sure to specify the desired/expected Locale rather than rely on the JVM's current default which can change at any moment during runtime(!).

String input = "January 2, 2015";
DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedDate ( FormatStyle.LONG );
formatter = formatter.withLocale ( Locale.US );
LocalDate localDate = LocalDate.parse ( input , formatter );

Dump to console.

System.out.println ( "input: " + input + " | localDate: " + localDate );

input: January 2, 2015 | localDate: 2015-01-02

Answer 3

The highly regarded Joda Time library is also worth a look. This is basis for the new date and time api that is pencilled in for Java 7. The design is neat, intuitive, well documented and avoids a lot of the clumsiness of the original java.util.Date / java.util.Calendar classes.

Joda's DateFormatter can parse a String to a Joda DateTime .

Answer 4

试试这个：

DateFormat.parse(String)

Answer 5

The DateFormat class has a parse method.

See DateFormat for more information.