I thinking what is the best way in Java to parse the String with this format dd/MM/yyyy [to dd/MM/yyyy]. The string with the [] are optional and dd stand for the 2 digit presentation of dates, MM is the 2 digit presentation of month and yyyy is the 4 digit presentation of year.

Update

Thanks guys for the fast response, however I forgot to tell you the [] is to symbolize optional, there is no [] in the string a sample String might be

• 22/01/2010
• 22/01/2010 to 23/01/2010
• null

Current I wrote the code this way, work but is ugly =(

String _daterange = (String) request.getParamet开发者_运维问答er("daterange");
    Date startDate = null, endDate = null;
    // Format of incoming dateRange is 
    if (InputValidator.requiredValidator(_daterange)) {
        String[] _dateRanges = _daterange.toUpperCase().split("TO");
        try {
            startDate = (_dateRanges.length > 0) ? sdf.parse(_dateRanges[0]) : null;
            try{
                endDate = (_dateRanges.length > 1) ? sdf.parse(_dateRanges[1]) : null;
            }catch(Exception e){
                endDate = null;
            }
        } catch (Exception e) {
            startDate = null;
        }
    }

Use java.text.DateFormat and java.text.SimpleDateFormat to do it.

DateFormat sourceFormat = new SimpleDateFormat("dd/MM/yyyy");
String dateAsString = "25/12/2010";
Date date = sourceFormat.parse(dateAsString);

UPDATE:

If you have two Dates hiding in that String, you'll have to break them into two parts. I think others have pointed out the "split" idea. I'd just break at whitespace and throw the "TO" away.

Don't worry about efficiency. Your app is likely to be riddled with inefficiencies much worse than this. Make it work correctly and refactor it only if profiling tells you that this snippet is the worst offender.

tl;dr

LocalDate.parse( 
    "22/01/2010" , 
    DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) 
)

…more…

// String input is:
// (a) long: "22/01/2010 to 23/01/2010". 
// (b) short: "22/01/2010".
// (c) null.

DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd/MM/uuuu" ) ;

if( input.length() == 24 ) {           // Ex: "22/01/2010 to 23/01/2010"
    List<LocalDate> lds = new ArrayList<>( 2 );
    String[] inputs = input.split( " to " );
    for( String nthInput : inputs ) {
        LocalDate ld = LocalDate.parse( nthInput , f ) ;
        lds.add( ld );
    }
    … // Do what you want with `LocalDate` objects collection.

} else if( input.length() == 10 ) {    // Ex: "22/01/2010"
    LocalDate ld = LocalDate.parse( input , f ) ;
    … // Do what you want with `LocalDate` object.

} else if( null == input ) {
    … // Decide what you want to do for null input.

} else {
    System.out.println( "Unexpected input: " + input ) ;
}

See this code run live at IdeOne.com.

Using java.time

The other Answers use troublesome old date-time classes that are now legacy, supplanted by the java.time classes.

As for handling multiple types of strings, look at the length of the string.

if( input.length() == 10 ) { … }

If long, split on the 4-character substring “ to ”.

String[] inputs = "22/01/2010 to 23/01/2010".split( " to " );

Parse the date string as a LocalDate.

DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd/MM/uuuu" );
LocalDate ld = LocalDate.parse( "22/01/2010" , f );

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.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, 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 Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). 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.

Something like this should do the trick:

String input = "02/08/2010 [to 31/12/2010]";
DateFormat format = new SimpleDateFormat("dd/MM/yyyy");
Date d  = format.parse(input.split(" ")[0]);
System.out.println(d) ;

you can do something like this -

String input = "02/08/2010 [to 31/12/2010]";
    java.text.DateFormat format = new java.text.SimpleDateFormat("dd/MM/yyyy");
    java.util.Date d = null;
    try {
        d = format.parse(input.split(" ")[0]);
    } catch (java.text.ParseException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    System.out.println(d) ;

if string with the [] is not present still input.split(" ")[0] will return the first string only.