how to extract date from the given filename in java

Question

I have my file names as below

1. C:\\Users\\name\\Documents\\repository\\zzz\\xxx_yyy\\new\\aaa_bbb_ccc_ddd_eee_ZZ_E_20160801_20160831_v1-0.csv
2. C:\\Users\\name\\Documents\\repository\\zzz\\xxx_yyy\\new\\aaa_bbb_ppp_ccc_ddd_eee_ZZ_E_20160801_20160831_v1-0.csv

I have to write a single java script for both the file format to extract both the dates from each filename.

Can you please help.

Answer 1

You should use Regular expressions to extract dates from filenames like these.

private static Date[] extractDatesFromFileName(File file) throws ParseException {
    Date[] dates = new Date[2];

    SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyyMMdd");

    String regex = ".*(\\d{8})_(\\d{8}).*";
    Pattern pattern = Pattern.compile(regex);
    Matcher m = pattern.matcher(file.getName());
    if (m.find()) {
        dates[0] = dateFormatter.parse(m.group(1));
        dates[1] = dateFormatter.parse(m.group(2));
    }
    System.out.println(dates[0]);
    System.out.println(dates[1]);
    return dates;
}

Little explanation:

In regex .*(\\\\d{8})_(\\\\d{8}).* :

• .* stands for any sing repeated from zero to unlimited times
• (\\\\d{8}) stands for exactly eight digits (if they are in brackets they are considered capturing groups , we have 2 capturing groups in this regex, one for each date)
• _ stands for _ sign :)

If filename matches provided pattern both dates are extracted, parsed and returned as array. You should add some error handling etc.

Answer 2

If you mean a Java script (not Javascript) you can use regexp, something like the following:

String in = "C:\\Users\\name\\Documents\\repository\\zzz\\xxx_yyy\\new\\aaa_bbb_ppp_ccc_ddd_eee_ZZ_E_20160801_20160831_v1-0.csv";
Pattern p = Pattern.compile("_(\\d{8})_v1-0");
Matcher m = p.matcher(in);
if (m.find()){
    System.out.println(m.group(1));
}

Answer 3

I think you want to extract two dates which are present in each file path. This could be done as follows:

String filename1 = "C:\\Users\\name\\Documents\\repository\\zzz\\xxx_yyy\\new\\aaa_bbb_ccc_ddd_eee_ZZ_E_20160801_20160831_v1-0.csv";
Pattern p = Pattern.compile("[0-9]{8}+_[0-9]{8}+");
Matcher m = p.matcher(filename1);
String[] dateStrArr = m.find()?m.group(0).split("_"): null;

First date will be in 0 index and second date will be in 1 index position.

Same goes for second file name. Hope this helps.

Also once extracted you can convert them to date object using SimpleDateFormat.