java 程序接受任何格式的日期作为输入并打印月份，

Question

java program to accept any format of date as input and print the month,

Is it possible

I tried the following,any other alternative ways/ideas??

import java.text.*;

import java.util.*;


public class PrintMonth3{


    public static void main(String args[])throws Exception{

    String patterns[]={"dd.MM.yyyy","dd.MM.yy","dd.MMM.yyyy","dd.MMM.yy","d.MM.yyyy"};

    String input="4.06.2011";

    for(int i=0;i<patterns.length;i++)
        doPrintMonth(patterns[i],input);

    System.out.println("\nNot a valid date format..");


    }



    public  static void doPrintMonth( String pattern,String input ) {


    try{
    SimpleDateFormat sdf=new SimpleDateFormat(pattern);

    Date output=sdf.parse(input);


    String mon[]={"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};
    int m=output.getMonth();
    System.out.println("\n\t" + mon[m] );
    System.exit(0);
    }
    catch(Exception e){}    


    }


}

Answer 1

No, it's not. How would it distinguish 01/02/2011 (dd/MM/yyyy) and 01/02/2011 (MM/dd/yyyy)?

Answer 2

Within reason, yes. Here's a working example that accepts a variety of formats.

I'm assuming a German / European format like this:

DD. MM. YYYY HH:MM:SS:MMMM

(which means that I can't match any date format where the month comes first)

Here's the class:

public class VariableDateParser {

    private static final Pattern DATE_PATTERN = Pattern
    .compile("((?:(?:\\d+(?:[./]\\s*)?)+)?)\\s*((?:(?:\\d+[:]?)+)?)");

    public Date getDate(final String dateString) {
        final Calendar calendar = Calendar.getInstance();
        final Matcher matcher = DATE_PATTERN.matcher(dateString);
        if (matcher.matches()) {
            final String dateGroup = matcher.group(1).trim();
            if (!"".equals(dateGroup)) {
                final Iterator<Integer> fields = Arrays.asList(
                    Calendar.DATE, Calendar.MONTH, Calendar.YEAR).iterator();
                final String[] items = dateGroup.split("\\D+");
                for (final String item : items) {
                    if ("".equals(item))
                        break;
                    else if (fields.hasNext()) {
                        final Integer field = fields.next();
                        calendar.set(field, Integer.parseInt(item) -
                           // months are 0-based, grrrr!!!
                           (field.equals(Calendar.MONTH) ? 1 : 0));
                    } else {
                        throw new IllegalArgumentException(
                            "Bad date part: " + dateGroup);
                    }
                }
            }
            final String timeGroup = matcher.group(2).trim();
            if (!"".equals(timeGroup)) {
                final Iterator<Integer> fields = Arrays.asList(
                    Calendar.HOUR, Calendar.MINUTE, Calendar.SECOND,
                    Calendar.MILLISECOND).iterator();
                final String[] items = timeGroup.split("\\D+");
                for (final String item : items) {
                    if ("".equals(item))
                        break;
                    else if (fields.hasNext()) {
                        final Integer field = fields.next();
                        calendar.set(field, Integer.parseInt(item));
                    } else {
                        throw new IllegalArgumentException(
                            "Bad time part: " + timeGroup);
                    }
                }
            }

        } else
            throw new IllegalArgumentException(
                "Bad date string: " + dateString);
        return calendar.getTime();
    }

}

Test Code:

public static void main(final String[] args) {
    VariableDateParser parser = new VariableDateParser();
    DateFormat df = DateFormat.getDateTimeInstance(
        DateFormat.MEDIUM, DateFormat.LONG, Locale.GERMAN);
    System.out.println(df.format(parser.getDate("11")));
    System.out.println(df.format(parser.getDate("11. 10.")));
    System.out.println(df.format(parser.getDate("11. 10. 4")));
    System.out.println(df.format(parser.getDate("11. 10. 2004")));
    System.out.println(df.format(parser.getDate("11. 10. 2004 11")));
    System.out.println(df.format(parser.getDate("11. 10. 2004 11:35")));
    System.out.println(df.format(parser.getDate("11. 10. 2004 11:35:18")));
    System.out.println(df.format(parser.getDate("11. 10. 2004 11:35:18:123")));
    System.out.println(df.format(parser.getDate("11:35")));
    System.out.println(df.format(parser.getDate("11:35:18")));
    System.out.println(df.format(parser.getDate("11:35:18:123")));
}

Output:

11.05.2011 15:57:24 MESZ
11.10.2011 15:57:24 MESZ
11.10.0004 15:57:24 MEZ
11.10.2004 15:57:24 MESZ
11.10.2004 23:57:24 MESZ
11.10.2004 23:35:24 MESZ
11.10.2004 23:35:18 MESZ
11.10.2004 23:35:18 MESZ
01.05.2011 13:35:24 MESZ
01.05.2011 13:35:18 MESZ
01.05.2011 13:35:18 MESZ

Note:

This is a quick proof of concept, not a serious attempt of writing such a class. This will match many invalid formats and ignore many valid ones.

Answer 3

For a wide range of formats, yes it is possible. For any format, no it is not. Consider the simple problem of British vs American dates eg is 03/04/10 the third of april or the fourth of march?

Answer 4

No, it is not possible.

Proof by counter example: 10/11/12 . This is a 'valid' format... but what is the month?

Answer 5

It's possible only if you also tell it what the format is, for instance with the Locale .

Answer 6

Technically its not but what you can do is provide some options to get the user to choose their format. If you are writing this in a GUI then you might want to use radio buttons and put them in a radio group. Otherwise if this is just for use within the compiler (such as a school program) then just use a switch statement like so:

Scanner kbReader = new Scanner(System.in);
String format = kbReader.next();//they might enter mm/dd/yy or any format you want.
switch(format)
{
  case "mm/dd/yy": //do coding here
                      break;
  case "dd/mm/yy": //do coding here
                      break;
}

just like that or you could just use a series of if-else statements because that is basically what a switch statement is.