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Saturday, 30 June 2018

Commons IO - FileAlterationObserver

Commons IO - FileAlterationObserver



Represents the state of files below a root directory, checks the filesystem and notifies listeners of create, change or delete events.

Class Declaration

Following is the declaration for org.apache.commons.io.monitor.FileAlterationObserver Class −
public class FileAlterationObserver
   extends Object implements Serializable

Example of FileAlterationObserver Class

Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
IOTester.java
import java.io.File;
import java.io.IOException;

import org.apache.commons.io.FileDeleteStrategy;
import org.apache.commons.io.FileUtils;
import org.apache.commons.io.monitor.FileAlterationListenerAdaptor;
import org.apache.commons.io.monitor.FileAlterationMonitor;
import org.apache.commons.io.monitor.FileAlterationObserver;

public class IOTester {
   public static void main(String[] args) {
      try {
         usingFileAlterationObserver();
      } catch(IOException e) {
         System.out.println(e.getMessage());
      }
   }

   public static void usingFileAlterationObserver() throws IOException {
      //get the file object
      File inputFile = FileUtils.getFile("input.txt");
      String absolutePath = inputFile.getAbsolutePath();
      String parent = absolutePath.substring(0,absolutePath.indexOf("input.txt"));   
      File parentDirectory = FileUtils.getFile(parent);

      FileAlterationObserver observer = new FileAlterationObserver(parentDirectory);

      observer.addListener(new FileAlterationListenerAdaptor() {

         @Override
         public void onDirectoryCreate(File file) {
            System.out.println("Folder created: " + file.getName());
         }

         @Override
         public void onDirectoryDelete(File file) {
            System.out.println("Folder deleted: " + file.getName());
         } 

         @Override
         public void onFileCreate(File file) {
            System.out.println("File created: " + file.getName());
         }

         @Override
         public void onFileDelete(File file) {
            System.out.println("File deleted: " + file.getName());
         }  
      });

      //create a monitor to check changes after every 500 ms
      FileAlterationMonitor monitor = new FileAlterationMonitor(500, observer);

      try {
         monitor.start();

         //create a new directory
         File newFolder = new File("test");
         File newFile = new File("test1");

         newFolder.mkdirs();
         Thread.sleep(1000);
         newFile.createNewFile();
         Thread.sleep(1000);
         FileDeleteStrategy.NORMAL.delete(newFolder);
         Thread.sleep(1000);
         FileDeleteStrategy.NORMAL.delete(newFile);
         Thread.sleep(1000);

         monitor.stop(10000);

      } catch(IOException e) {
         System.out.println(e.getMessage());
      } catch(InterruptedException e) {
         System.out.println(e.getMessage());
      } catch (Exception e) {
         System.out.println(e.getMessage());
      }
   }
}

Output

It will print the following result.
Folder created: test
File created: test1
Folder deleted: test
File deleted: test1

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