How to delete older files

Question

I'm going to make a logic to erase files from a year ago. Does anyone know if there is a process that allows you to read the oldest file first without reading the entire file before erasing it with the delete() method using the File Class?

I'm looking for a way to get the same performance even if there are 10,000 to 1 million files.

public class FileValidation {
 
    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();    
        long todayMil = cal.getTimeInMillis();    
        long oneDayMil = 24 * 60 * 60 * 1000;    
 
        Calendar fileCal = Calendar.getInstance();
        Date fileDate = null;
 
        File path = new File("C:\\test");
        File[] list = path.listFiles();        
 
        for (int j = 0; j < list.length; j++) {
 
            fileDate = new Date(list[j].lastModified());
 
            fileCal.setTime(fileDate);
            long diffMil = todayMil - fileCal.getTimeInMillis();
 
            int diffDay = (int) (diffMil / oneDayMil);
 
            if (diffDay > 3 && list[j].exists()) {
                list[j].delete();
            }
 
        }
 
    }
 
}

Answer 1

It is generally better to avoid Date and File handling. In newer JDKs the Path, Files and java.time.* classes gives much better control over filesystem and time handling.

It is easy to setup a reference time (example 365 days ago), and use Files.find to perform the scan of matching files older than this period:

Path dir = Path.of("C:/test");
Instant refTime = Instant.now().minus(Duration.ofDays(365));

try(var files = Files.find(dir, /*depth*/ Integer.MAX_VALUE, (p,a) -> 
        a.isRegularFile() && a.lastModifiedTime().toInstant().isBefore(refTime))) {
    files.forEach(System.out::println);
}

Change the above to perform delete, I've not left it there in case someone accidentally runs it, replace action with:

files.forEach(p -> {
    try {
        Files.delete(p);
    } catch(IOException io) {
        throw new UncheckedIOException(io);
    }
});