org.apache.commons.io.comparator.LastModifiedFileComparator Example

Prasad SayaDecember 31st, 2014Last Updated: January 12th, 2015

0 53 2 minutes read

Apache Commons IO is a library of utilities to assist with developing IO functionality. org.apache.commons.io.comparator package provides various Comparator implementations for Files. LastModifiedFileComparator is one of the classes.

This class can be used to sort lists or arrays of files (File objects) by their last modified date/time. The File class’s lastModified() method is used for comparing two files; the method returns the last modified time of the file as a long.

The class is from Apache Commons IO 2.4. Note the commons-io-2.4.jar file is required in the classpath to compile and run the examples. This library can be downloaded from the Apache Commons website.

This article shows a usage example. The example is tested on Windows operating system. The Apache Commons IO 2.4 API usage requires Java SE 6 or greater.

1. An Example

This example sorts files in a directory by using the LastModifiedFileComparator‘s sort() method.

The example program takes a directory with files as input File objects. These file objects are copied to a File array. Then the array is sorted using the LastModifiedFileComparator class’s sort() method.

Note that a real directory and files are required to run the example.

1.1. The Code

LastModFileComparatorExample.java

import org.apache.commons.io.comparator.LastModifiedFileComparator;
import java.io.File;
import java.util.Date;
import java.text.SimpleDateFormat;

public class LastModFileComparatorExample {

    public static void main(String [] args) {

        LastModifiedFileComparator comparator = new LastModifiedFileComparator();

        System.out.println("### Input files ###");
        File dir = new File("X:\\testdir\\");
        File [] files = dir.listFiles();
        printArrayContents(files);

        System.out.println("### Array sorted ###");
        files = comparator.sort(files);
        printArrayContents(files);
    }

    private static void printArrayContents(File [] files) {

        SimpleDateFormat formatter = new SimpleDateFormat("yyyy MMM dd HH:mm");

        for (File file : files) {

            Date date = new Date(file.lastModified());
            System.out.println(formatter.format(date) + "    " + file.getName());
        }

        System.out.println("");
    }
}

1.2. The Output

### Input files ###
2012 Nov 17 13:30    A Difinitive Guide To HTML5.pdf
2014 Dec 15 14:52    BoxingExample.java
2013 May 15 12:45    jdbc4.0-spec.pdf
2014 Nov 17 15:45    screenshots.docx
2012 Jun 17 10:41    Upgrade to Java SE 7 Programmer.webarchive
2014 Dec 10 16:38    WatchEventExample.java

### Array sorted ###
2012 Jun 17 10:41    Upgrade to Java SE 7 Programmer.webarchive
2012 Nov 17 13:30    A Difinitive Guide To HTML5.pdf
2013 May 15 12:45    jdbc4.0-spec.pdf
2014 Nov 17 15:45    screenshots.docx
2014 Dec 10 16:38    WatchEventExample.java
2014 Dec 15 14:52    BoxingExample.java

From the output:

Input files: Note that the input files are listed by their names.
Array sorted: The output shows the sorted array of files ordered by their last modified date and time.