Apache Commons IO - Quick Guide

Apache Commons IO library provides various utility classes for common operations for File IO covering wide range of use cases. It helps avoid writing boilerplate code. Apache Commons IO library provides classes for following categories:
Utility classes − These classes under org.apache.commons.io package provides file and string comparison. Following are some of the examples.

IOUtils − Provides utility methods for reading, writing and copying files. The methods works with InputStream, OutputStream, Reader and Writer.
FilenameUtils − Provides method to work with file names without using File Object. It works on different operating systems in similar way.
FileUtils − Provides method to manipulates files like moving, opening, checking existence, reading of file etc. These methods use File Object.
IOCase − Provides method for string manipulation and comparison.
FileSystemUtils − Provides method to get the free space on a disk drive.
LineIterator − Provides a flexible way to work with a line-based file.


Utility classes − These classes under org.apache.commons.io package provides file and string comparison. Following are some of the examples.
IOUtils − Provides utility methods for reading, writing and copying files. The methods works with InputStream, OutputStream, Reader and Writer.
IOUtils − Provides utility methods for reading, writing and copying files. The methods works with InputStream, OutputStream, Reader and Writer.
FilenameUtils − Provides method to work with file names without using File Object. It works on different operating systems in similar way.
FilenameUtils − Provides method to work with file names without using File Object. It works on different operating systems in similar way.
FileUtils − Provides method to manipulates files like moving, opening, checking existence, reading of file etc. These methods use File Object.
FileUtils − Provides method to manipulates files like moving, opening, checking existence, reading of file etc. These methods use File Object.
IOCase − Provides method for string manipulation and comparison.
IOCase − Provides method for string manipulation and comparison.
FileSystemUtils − Provides method to get the free space on a disk drive.
FileSystemUtils − Provides method to get the free space on a disk drive.
LineIterator − Provides a flexible way to work with a line-based file.
LineIterator − Provides a flexible way to work with a line-based file.
Filter classes − Filter classes under org.apache.commons.io.filefilter package provides methods to filter files based on logical criterias instead of string based tedious comparisons. Following are some of the examples.

NameFileFilter − Filters file-names for a name.
WildcardFileFilter − Filters files using the supplied wildcards.
SuffixFileFilter − Filters files based on suffix. This is used in retrieving all the files of a particular type.
PrefixFileFilter − Filters files based on prefix.
OrFileFilter − Provides conditional OR logic across a list of file filters. Returns true if any filters in the list return true. Otherwise, it returns false. 
AndFileFilter − Provides conditional And logic across a list of file filters. Returns false if any filters in the list return false. Otherwise, it returns true.


Filter classes − Filter classes under org.apache.commons.io.filefilter package provides methods to filter files based on logical criterias instead of string based tedious comparisons. Following are some of the examples.
NameFileFilter − Filters file-names for a name.
NameFileFilter − Filters file-names for a name.
WildcardFileFilter − Filters files using the supplied wildcards.
WildcardFileFilter − Filters files using the supplied wildcards.
SuffixFileFilter − Filters files based on suffix. This is used in retrieving all the files of a particular type.
SuffixFileFilter − Filters files based on suffix. This is used in retrieving all the files of a particular type.
PrefixFileFilter − Filters files based on prefix.
PrefixFileFilter − Filters files based on prefix.
OrFileFilter − Provides conditional OR logic across a list of file filters. Returns true if any filters in the list return true. Otherwise, it returns false. 
OrFileFilter − Provides conditional OR logic across a list of file filters. Returns true if any filters in the list return true. Otherwise, it returns false. 
AndFileFilter − Provides conditional And logic across a list of file filters. Returns false if any filters in the list return false. Otherwise, it returns true.
AndFileFilter − Provides conditional And logic across a list of file filters. Returns false if any filters in the list return false. Otherwise, it returns true.
File Monitor classes − File monitor classes under org.apache.commons.io.monitor package provides control to track changes in a specific file or folder and allows to do action accordingly on the changes. Following are some of the examples.
File Monitor classes − File monitor classes under org.apache.commons.io.monitor package provides control to track changes in a specific file or folder and allows to do action accordingly on the changes. Following are some of the examples.
FileEntry − Provides the state of a file or directory, File attributes at a point in time.
FileEntry − Provides the state of a file or directory, File attributes at a point in time.
FileAlterationObserver − Represents the state of files below a root directory, checks the filesystem and notifies listeners of create, change or delete events.
FileAlterationObserver − Represents the state of files below a root directory, checks the filesystem and notifies listeners of create, change or delete events.
FileAlterationMonitor − Represent a thread that spawns a monitoring thread triggering any registered FileAlterationObserver at a specified interval.
FileAlterationMonitor − Represent a thread that spawns a monitoring thread triggering any registered FileAlterationObserver at a specified interval.
Comparator classes − File monitor classes under org.apache.commons.io.comparator package allow to compare and sort files and directories easily.

NameFileComparator − Compare the names of two files.
SizeFileComparator − Compare the size of two files.
LastModifiedFileComparator − Compare the last modified dates of two files.


Comparator classes − File monitor classes under org.apache.commons.io.comparator package allow to compare and sort files and directories easily.

NameFileComparator − Compare the names of two files.
NameFileComparator − Compare the names of two files.
SizeFileComparator − Compare the size of two files.
SizeFileComparator − Compare the size of two files.
LastModifiedFileComparator − Compare the last modified dates of two files.
LastModifiedFileComparator − Compare the last modified dates of two files.
Stream classes − There are multiple implementation of InputStream under org.apache.commons.io.input package and of OutputStream under org.apache.commons.io.output package to do useful tasks on streams. Following are some of the examples.

NullOutputStream − absorbs all data sent with any error.
TeeOutputStream − sends output to two streams.
ByteArrayOutputStream − faster version of JDK class.
CountingOutputStream − Counts the number of bytes passed through the stream.
CountingOutputStream − Counts the number of bytes passed through the stream.
ProxyOutputStream − Changes the calls to proxied stream.
LockableFileWriter − A FileWriter to create lock files and allow simple cross thread file lock handling.


Stream classes − There are multiple implementation of InputStream under org.apache.commons.io.input package and of OutputStream under org.apache.commons.io.output package to do useful tasks on streams. Following are some of the examples.
NullOutputStream − absorbs all data sent with any error.
NullOutputStream − absorbs all data sent with any error.
TeeOutputStream − sends output to two streams.
TeeOutputStream − sends output to two streams.
ByteArrayOutputStream − faster version of JDK class.
ByteArrayOutputStream − faster version of JDK class.
CountingOutputStream − Counts the number of bytes passed through the stream.
CountingOutputStream − Counts the number of bytes passed through the stream.
CountingOutputStream − Counts the number of bytes passed through the stream.
CountingOutputStream − Counts the number of bytes passed through the stream.
ProxyOutputStream − Changes the calls to proxied stream.
ProxyOutputStream − Changes the calls to proxied stream.
LockableFileWriter − A FileWriter to create lock files and allow simple cross thread file lock handling.
LockableFileWriter − A FileWriter to create lock files and allow simple cross thread file lock handling.
In this chapter, we will learn about the local environment setup of Apache Commons IO and how to set up the path of Commons IO for Windows 2000/XP, Windows 95/98/ME etc. We will also understand about some popular java editors and how to download Commons IO archive.
First of all, you need to have Java Software Development Kit (SDK) installed on your system. To verify this, execute any of the two commands depending on the platform you are working on.
If the Java installation has been done properly, then it will display the current version and specification of your Java installation. A sample output is given in the following table.
Open command console and type −
\>java -version
java version "11.0.11" 2021-04-20 LTS
Java(TM) SE Runtime Environment 18.9 (build 11.0.11+9-LTS-194)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.11+9-LTS-194, mixed mode)
Open command terminal and type −
$java -version
java version "11.0.11" 2021-04-20 LTS
Open JDK Runtime Environment 18.9 (build 11.0.11+9-LTS-194)
Open JDK 64-Bit Server VM (build 11.0.11+9-LTS-194, mixed mode)
We assume the readers of this tutorial have Java SDK version 11.0.11 installed on their system.
We assume the readers of this tutorial have Java SDK version 11.0.11 installed on their system.
In case you do not have Java SDK, download its current version from www.oracle.com/technetwork/java/javase/downloads/index.html and have it installed.

In case you do not have Java SDK, download its current version from www.oracle.com/technetwork/java/javase/downloads/index.html and have it installed.
Set the environment variable JAVA_HOME to point to the base directory location where Java is installed on your machine. For example,
Windows
Set JAVA_HOME to C:\ProgramFiles\java\jdk11.0.11
Linux
Export JAVA_HOME = /usr/local/java-current
Append the full path of Java compiler location to the System Path.
Windows
Append the String "C:\Program Files\Java\jdk11.0.11\bin" to the end of the system variable PATH.
Linux
Export PATH = $PATH:$JAVA_HOME/bin/
Execute the command java -version from the command prompt as explained above.
To write your Java programs, you need a text editor. There are many sophisticated integrated development environment (IDEs) available in the market. But for now, you can consider one of the following −
Notepad − On Windows machine you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad.
Notepad − On Windows machine you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad.
Netbeans − It is a Java IDE that is open-source and free which can be downloaded from www.netbeans.org/index.html.
Netbeans − It is a Java IDE that is open-source and free which can be downloaded from www.netbeans.org/index.html.
Eclipse − It is also a Java IDE developed by the eclipse open-source community and can be downloaded from www.eclipse.org.
Eclipse − It is also a Java IDE developed by the eclipse open-source community and can be downloaded from www.eclipse.org.
Download the latest version of Apache Common IO jar file from commons-io-2.11.0-bin.zip. At the time of writing this tutorial, we have downloaded commons-io-2.11.0-bin.zip and copied it into C:\>Apache folder.
Set the APACHE_HOME environment variable to point to the base directory location where Apache jar is stored on your machine. Assuming, we've extracted commons-io-2.11.0-bin.zip in Apache folder on various Operating Systems as follows.
Set the CLASSPATH environment variable to point to the Common IO jar location. Assuming, you have stored commons-io-2.11.0-bin.zip in Apache folder on various Operating Systems as follows.
Provides utility methods for reading, writing and copying files. The methods works with InputStream, OutputStream, Reader and Writer.
Following is the declaration for org.apache.commons.io.IOUtils Class -
public class IOUtils
   extends Object
Provides static utility methods for input/output operations.
Provides static utility methods for input/output operations.
toXXX() - reads data from a stream.
toXXX() - reads data from a stream.
write() - write data to a stream.
write() - write data to a stream.
copy() - copy all data to a stream to another stream.
copy() - copy all data to a stream to another stream.
contentEquals - compare the contents of two streams.
contentEquals - compare the contents of two streams.
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
IOTester.java
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import org.apache.commons.io.IOUtils;

public class IOTester {
   public static void main(String[] args) {
      try{
         //Using BufferedReader
         readUsingTraditionalWay();

         //Using IOUtils
         readUsingIOUtils();
      }catch(IOException e){
         System.out.println(e.getMessage());
      }
   }

   //reading a file using buffered reader line by line
   public static void readUsingTraditionalWay() throws IOException{
      try (BufferedReader bufferReader 
         = new BufferedReader( 
            new InputStreamReader(  
               new FileInputStream("input.txt") ) )) {
         String line;
         while ( ( line = bufferReader.readLine() ) != null ) {
            System.out.println( line );
         }
      }
   }

   //reading a file using IOUtils in one go
   public static void readUsingIOUtils() throws IOException {
      try(InputStream in = new FileInputStream("input.txt")){
         System.out.println( IOUtils.toString( in , "UTF-8") );
      }
   }
}
It will print the following result.
Welcome to TutorialsPoint. Simply Easy Learning.
Welcome to TutorialsPoint. Simply Easy Learning.

Provides method to manipulates files like moving, opening, checking existence, reading of file etc. These methods use File Object.
Following is the declaration for org.apache.commons.io.FileUtils Class -
public class FileUtils
   extends Object
Methods to write to a file.
Methods to write to a file.
Methods to read from a file.
Methods to read from a file.
Methods to make a directory including parent directories.
Methods to make a directory including parent directories.
Methods to copy files and directories.
Methods to copy files and directories.
Methods to delete files and directories.
Methods to delete files and directories.
Methods to convert to and from a URL.
Methods to convert to and from a URL.
Methods to list files and directories by filter and extension.
Methods to list files and directories by filter and extension.
Methods to compare file content.
Methods to compare file content.
Methods to file last changed date.
Methods to file last changed date.
Methods to calculating a checksum.
Methods to calculating a checksum.
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 java.nio.charset.Charset;

import org.apache.commons.io.FileUtils;

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

   public static void usingFileUtils() throws IOException {
      //get the file object
      File file = FileUtils.getFile("input.txt");

      //get the temp directory
      File tmpDir = FileUtils.getTempDirectory();

      System.out.println(tmpDir.getName());

      //copy file to temp directory
      FileUtils.copyFileToDirectory(file, tmpDir);

      //create a new file
      File newTempFile = FileUtils.getFile(tmpDir, file.getName());

      //get the content
      String data = FileUtils.readFileToString(newTempFile, Charset.defaultCharset());

      //print the content
      System.out.println(data);
   }
}
It will print the following result.
Temp
Welcome to TutorialsPoint. Simply Easy Learning.

Provides method to work with file names without using File Object. It works on different operating systems in similar way. This class solves problems when moving from a Windows based development machine to a Unix based production machine.
Following is the declaration for org.apache.commons.io.FilenameUtils Class -
public class FilenameUtils
   extends Object
This class defines six components within a filename. Consider an example location as C:\dev\project\file.txt. Then the components are
Prefix - C:\
Prefix - C:\
Relative Path - dev\project\
Relative Path - dev\project\
Absolute path - C:\dev\project\
Absolute path - C:\dev\project\
Name - file.txt
Name - file.txt
Base name - file
Base name - file
Extension - txt
Extension - txt
To identify a directory, add a separator to file name.
IOTester.java
import java.io.IOException;
import org.apache.commons.io.FilenameUtils;

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

   public static void usingFilenameUtils() throws IOException {
      String path = "C:\\dev\\project\\file.txt";
      System.out.println("Full Path: " +FilenameUtils.getFullPath(path));
      System.out.println("Relative Path: " +FilenameUtils.getPath(path));
      System.out.println("Prefix: " +FilenameUtils.getPrefix(path));
      System.out.println("Extension: " + FilenameUtils.getExtension(path));
      System.out.println("Base: " + FilenameUtils.getBaseName(path));
      System.out.println("Name: " + FilenameUtils.getName(path));

      String filename = "C:/commons/io/../lang/project.xml";
      System.out.println("Normalized Path: " + FilenameUtils.normalize(filename));
   }
}
It will print the following result.
Full Path: C:\dev\project\
Relative Path: dev\project\
Prefix: C:\
Extension: txt
Base: file
Name: file.txt
Normalized Path: C:\commons\lang\project.xml

Provides method to get the free space on a disk drive.
Following is the declaration for org.apache.commons.io.FileSystemUtils Class -
public class FileSystemUtils
   extends Object
IOTester.java
import java.io.IOException;

import org.apache.commons.io.FileSystemUtils;

public class IOTester {
   public static void main(String[] args) {
      try{
         System.out.println("Free Space " + FileSystemUtils.freeSpaceKb("C:/") + " Bytes");
      }catch(IOException e){
         System.out.println(e.getMessage());
      }
   }
}
It will print the following result.
Free Space 61355640 kb

Enumeration of IO case sensitivity. Different Operating systems have different rules for case-sensitivity for file names. For example Windows is case-insensitive for file naming while Unix is case-sensitive. IOCase captures that difference, provides an enumeration to control how filename comparisons should be performed. It also provides methods to use the enumeration to perform comparisons.
Following is the declaration for org.apache.commons.io.IOCase Enum -
public enum IOCase
   extends Enum<IOCase>
      implements Serializable
IOTester.java
import java.io.IOException;
import org.apache.commons.io.IOCase;

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

   public static void usingIOCase() throws IOException {
      String text = "Welcome to TutorialsPoint. Simply Easy Learning.";
      String text1 = "WELCOME TO TUTORIALSPOINT. SIMPLY EASY LEARNING.";

      System.out.println("Ends with Learning (case sensitive): " +
      IOCase.SENSITIVE.checkEndsWith(text1, "Learning."));

      System.out.println("Ends with Learning (case insensitive): " +
      IOCase.INSENSITIVE.checkEndsWith(text1, "Learning."));

      System.out.println("Equality Check  (case sensitive): " +
      IOCase.SENSITIVE.checkEquals(text, text1));

      System.out.println("Equality Check  (case insensitive): " +
      IOCase.INSENSITIVE.checkEquals(text, text1));
   }
}
It will print the following result.
Ends with Learning (case sensitive): false
Ends with Learning (case insensitive): true
Equality Check  (case sensitive): false
Equality Check  (case insensitive): true

Provides a flexible way to work with a line-based file.
Following is the declaration for org.apache.commons.io.LineIterator Class -
public class LineIterator
   extends Object
      implements Iterator<String>, Closeable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
Learn web technologies,
prepare exams,
code online,
all at one place.
IOTester.java
import java.io.File;
import java.io.IOException;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.LineIterator;

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

   public static void usingLineIterator() throws IOException {
      //get the file object
      File file = FileUtils.getFile("input.txt");

      try(LineIterator lineIterator = FileUtils.lineIterator(file)){
         System.out.println("Contents of input.txt");
         while (lineIterator.hasNext()) {
            System.out.println(lineIterator.next());
         }
      }
   }
}
It will print the following result.
Contents of input.txt
Welcome to TutorialsPoint. Simply Easy Learning.
Learn web technologies,
prepare exams,
code online,
all at one place.

Filters file-names for a name.
Following is the declaration for org.apache.commons.io.filefilter.NameFileFilter Class -
public class NameFileFilter
   extends AbstractFileFilter
      implements Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
Let's print all files and directories in the current directory and then filter a file whose name is Input.txt.
IOTester.java
import java.io.File;
import java.io.IOException;
import org.apache.commons.io.IOCase;
import org.apache.commons.io.filefilter.NameFileFilter;

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

   public static void usingNameFileFilter() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");
      //get names of all files and directory in current directory
      String[] files = currentDirectory.list();
      System.out.println("All files and Folders.\n");
      for ( int i = 0; i < files.length; i++ ) {
         System.out.println(files[i]);
      }
      System.out.println("\nFile with name input.txt\n");
      String[] acceptedNames = {"input", "input.txt"};
      String[] filesNames = currentDirectory.list( new NameFileFilter(acceptedNames, IOCase.INSENSITIVE) );

      for ( int i = 0; i < filesNames.length; i++ ) {
         System.out.println(filesNames[i]);
      }
   }
}
It will print the following result.
All files and Folders.

.classpath
.project
.settings
bin
input.txt
src

File with name input.txt

input.txt

Filters files using the supplied wildcards.
Following is the declaration for org.apache.commons.io.filefilter.WildcardFileFilter Class -
public class WildcardFileFilter
   extends AbstractFileFilter
      implements Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
Let's print all files and directories in the current directory and then filter a file whose name ends with t.
IOTester.java
import java.io.File;
import java.io.IOException;

import org.apache.commons.io.filefilter.WildcardFileFilter;

public class IOTester {
   public static void main(String[] args) {
      try{
         usingWildcardFileFilter();
      }catch(IOException e){
         System.out.println(e.getMessage());
      }
   }
   public static void usingWildcardFileFilter() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");
      //get names of all files and directory in current directory
      String[] files = currentDirectory.list();
      System.out.println("All files and Folders.\n");
      for ( int i = 0; i < files.length; i++ ) {
         System.out.println(files[i]);
      }
      System.out.println("\nFile name ending with t.\n");
      String[] filesNames = currentDirectory.list( new WildcardFileFilter("*t") );
      for ( int i = 0; i < filesNames.length; i++ ) {
         System.out.println(filesNames[i]);
      }
   }
}
It will print the following result.
All files and Folders.

.classpath
.project
.settings
bin
input.txt
src

File name ending with t

.project
input.txt

Filters files based on suffix. This is used in retrieving all the files of a particular type.
Following is the declaration for org.apache.commons.io.filefilter.SuffixFileFilter Class -
public class SuffixFileFilter
   extends AbstractFileFilter
      implements Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
Let's print all files and directories in the current directory and then filter a file with extension txt.
IOTester.java
import java.io.File;
import java.io.IOException;

import org.apache.commons.io.filefilter.SuffixFileFilter;

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

   public static void usingSuffixFileFilter() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");
      //get names of all files and directory in current directory
      String[] files = currentDirectory.list();
      System.out.println("All files and Folders.\n");
      for ( int i = 0; i < files.length; i++ ) {
         System.out.println(files[i]);
      }
      System.out.println("\nFile with extenstion txt\n");
      String[] filesNames = currentDirectory.list( new SuffixFileFilter("txt") );
      for ( int i = 0; i < filesNames.length; i++ ) {
         System.out.println(filesNames[i]);
      }
   }
}
It will print the following result.
All files and Folders.

.classpath
.project
.settings
bin
input.txt
src

File with extenstion txt

input.txt

Filters files based on prefix.
Following is the declaration for org.apache.commons.io.filefilter.PrefixFileFilter Class -
public class PrefixFileFilter
   extends AbstractFileFilter
      implements Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
Let's print all files and directories in the current directory and then filter a file with name starting with input.
IOTester.java
import java.io.File;
import java.io.IOException;

import org.apache.commons.io.filefilter.PrefixFileFilter;

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

   public static void usingPrefixFileFilter() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");
      //get names of all files and directory in current directory
      String[] files = currentDirectory.list();
      System.out.println("All files and Folders.\n");
      for ( int i = 0; i < files.length; i++ ) {
         System.out.println(files[i]);
      }
      System.out.println("\nFile starting with input\n");
      String[] filesNames = currentDirectory.list( new PrefixFileFilter("input") );
      for ( int i = 0; i < filesNames.length; i++ ) {
         System.out.println(filesNames[i]);
      }
   }
}
It will print the following result.
All files and Folders.

.classpath
.project
.settings
bin
input.txt
src

File with extenstion txt

input.txt

Provides conditional OR logic across a list of file filters. Returns true if any filters in the list return true. Otherwise, it returns false.
Following is the declaration for org.apache.commons.io.filefilter.OrFileFilter Class -
public class OrFileFilter
   extends AbstractFileFilter
      implements ConditionalFileFilter, Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
Let's print all files and directories in the current directory and then filter a file with name starting with . or ends with t.
IOTester.java
import java.io.File;
import java.io.IOException;

import org.apache.commons.io.filefilter.OrFileFilter;
import org.apache.commons.io.filefilter.PrefixFileFilter;
import org.apache.commons.io.filefilter.WildcardFileFilter;

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

   public static void usingOrFileFilter() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");
      //get names of all files and directory in current directory
      String[] files = currentDirectory.list();
      System.out.println("All files and Folders.\n");
      for ( int i = 0; i < files.length; i++ ) {
         System.out.println(files[i]);
      }
      System.out.println("\nFile starting with . or ends with t\n");
      String[] filesNames = currentDirectory.list(
         new OrFileFilter(new PrefixFileFilter("."), new WildcardFileFilter("*t")));
      for ( int i = 0; i < filesNames.length; i++ ) {
         System.out.println(filesNames[i]);
      }
   }
}
It will print the following result.
All files and Folders.

.classpath
.project
.settings
bin
input.txt
src

File starting with . or ends with t

.classpath
.project
.settings
input.txt

Provides conditional And logic across a list of file filters. Returns true if all filters in the list return true. Otherwise, it returns false.
Following is the declaration for org.apache.commons.io.filefilter.AndFileFilter Class -
public class AndFileFilter
   extends AbstractFileFilter
      implements ConditionalFileFilter, Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.

Let's print all files and directories in the current directory and then filter a file with name starting with . and ends with t.
IOTester.java
import java.io.File;
import java.io.IOException;

import org.apache.commons.io.filefilter.AndFileFilter;
import org.apache.commons.io.filefilter.PrefixFileFilter;
import org.apache.commons.io.filefilter.WildcardFileFilter;

public class IOTester {
   public static void main(String[] args) {
      try{
         usingAndFileFilter();
      }catch(IOException e){
         System.out.println(e.getMessage());
      }
   }
   public static void usingAndFileFilter() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");
      //get names of all files and directory in current directory
      String[] files = currentDirectory.list();
      System.out.println("All files and Folders.\n");
      for ( int i = 0; i < files.length; i++ ) {
         System.out.println(files[i]);
      }
      System.out.println("\nFile starting with . and ends with t\n");
      String[] filesNames = currentDirectory.list(
         new AndFileFilter(new PrefixFileFilter("."), new WildcardFileFilter("*t")));
      for ( int i = 0; i < filesNames.length; i++ ) {
         System.out.println(filesNames[i]);
      }
   }
}
It will print the following result.
All files and Folders.

.classpath
.project
.settings
bin
input.txt
src

File starting with . or ends with t

.project

Provides the state of a file or directory, File attributes at a point in time.
Following is the declaration for org.apache.commons.io.monitor.FileEntry Class -
public class FileEntry
   extends Object
      implements Serializable
FileEntry class object provides following file attributes at a point in time.
getName() - file name.
getName() - file name.
exists() - checks if file exists or not.
exists() - checks if file exists or not.
isDirectory() - checks if file is a directory.
isDirectory() - checks if file is a directory.
lastModified() - gives last modified date time.
lastModified() - gives last modified date time.
listFiles() - gives content of directory.
listFiles() - gives content of directory.
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.FileUtils;
import org.apache.commons.io.monitor.FileEntry;

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

   public static void usingFileEntry() throws IOException {
      //get the file object
      File file = FileUtils.getFile("input.txt");

      FileEntry fileEntry = new FileEntry(file);

      System.out.println("Monitored File: " + fileEntry.getFile());
      System.out.println("File name: " + fileEntry.getName());
      System.out.println("Is Directory: " + fileEntry.isDirectory());
   }
}
It will print the following result.
Monitored File: input.txt
File name: input.txt
Is Directory: false

Represents the state of files below a root directory, checks the filesystem and notifies listeners of create, change or delete events.
Following is the declaration for org.apache.commons.io.monitor.FileAlterationObserver Class -
public class FileAlterationObserver
   extends Object
      implements Serializable
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());
      }
   }
}
It will print the following result.
Folder created: test
File created: test1
Folder deleted: test
File deleted: test1

Representa a thread that spawns a monitoring thread triggering any registered FileAlterationObserver at a specified interval.
Following is the declaration for org.apache.commons.io.monitor.FileAlterationMonitor Class -
public final class FileAlterationMonitor
   extends Object
      implements Runnable

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

   public static void usingFileAlterationMonitor() 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());
      }
   }
}
It will print the following result.
Folder created: test
File created: test1
Folder deleted: test
File deleted: test1

Compare the names of two files. NameFileComparator can be used to sort lists or arrays of files using their name either in a case-sensitive, case-insensitive or system dependent case sensitive way.
Following is the declaration for org.apache.commons.io.comparator.NameFileComparator Class -
public class NameFileComparator
   extends Object
      implements Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
IOTester.java
import java.io.File;
import java.io.FileFilter;
import java.io.IOException;

import org.apache.commons.io.IOCase;
import org.apache.commons.io.comparator.NameFileComparator;
import org.apache.commons.io.filefilter.FileFileFilter;

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

   public static void usingNameFileComparator() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");

      NameFileComparator comparator = new NameFileComparator(IOCase.INSENSITIVE);

      File[] sortedFiles = comparator.sort(currentDirectory.listFiles((FileFilter)FileFileFilter.FILE));

      System.out.println("Sorted By Name: ");
      for(File file:sortedFiles){      
         System.out.println(file.getName());
      }
   }
}
It will print the following result.
Sorted By Name: 
.classpath
.project
input.txt

Compare the sizes of two files/directory. SizeFileComparator can be used to sort lists or arrays of files using their size or directories based on their no. of children.
Following is the declaration for org.apache.commons.io.comparator.SizeFileComparator Class -
public class SizeFileComparator
   extends Object
      implements Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
IOTester.java
import java.io.File;
import java.io.FileFilter;
import java.io.IOException;

import org.apache.commons.io.comparator.SizeFileComparator;
import org.apache.commons.io.filefilter.FileFileFilter;

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

   public static void usingSizeFileComparator() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");

      SizeFileComparator comparator = new SizeFileComparator();

      File[] sortedFiles = comparator.sort(currentDirectory.listFiles((FileFilter)FileFileFilter.FILE));

      System.out.println("Sorted By Size: ");
      for(File file:sortedFiles){      
         System.out.println(file.getName() + ", size(kb) :" + file.length());
      }
   }
}
It will print the following result.
Sorted By Size: 
input.txt, size:124
.project, size:382
.classpath, size:441

Compare the last modified dates of two files/directory. LastModifiedFileComparator can be used to sort lists or arrays of files/directories using their last modified dates.
Following is the declaration for org.apache.commons.io.comparator.LastModifiedFileComparator Class -
public class LastModifiedFileComparator
   extends Object
      implements Serializable
Here is the input file we need to parse −
Welcome to TutorialsPoint. Simply Easy Learning.
IOTester.java
import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.util.Date;

import org.apache.commons.io.comparator.LastModifiedFileComparator;
import org.apache.commons.io.filefilter.FileFileFilter;

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

   public static void usingLastModifiedFileComparator() throws IOException {
      //get the current directory
      File currentDirectory = new File(".");

      LastModifiedFileComparator comparator = new LastModifiedFileComparator();

      File[] sortedFiles = comparator.sort(currentDirectory.listFiles((FileFilter)FileFileFilter.FILE));

      System.out.println("Sorted By Last Modified date: ");
      for(File file:sortedFiles){      
         System.out.println(file.getName() + ", Modified on: " + new Date(file.lastModified()));
      }
   }
}
It will print the following result.
Sorted By Last Modified date: 
.project, Modified on: Thu Oct 12 19:06:45 IST 2017
.classpath, Modified on: Mon Nov 20 13:09:55 IST 2017
input.txt, Modified on: Mon Nov 20 19:27:55 IST 2017

It is an InputStream proxy that transparently writes a copy of all bytes read from the proxied stream to a given OutputStream. The proxied input stream is closed when the close() method on this proxy is called. It can be used to operate two streams collectively at a time.
Following is the declaration for org.apache.commons.io.input.TeeInputStream Class -
public class TeeInputStream
   extends ProxyInputStream

In this example, closing a TeeInputStream closes the TeeInputStream as well as TeeOutputStream objects.
IOTester.java
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

import org.apache.commons.io.input.TeeInputStream;
import org.apache.commons.io.output.TeeOutputStream;

public class IOTester {
   private static final String SAMPLE = "Welcome to TutorialsPoint. Simply Easy Learning.";

   public static void main(String[] args) {
      try{
         usingTeeInputStream();
      }catch(IOException e){
         System.out.println(e.getMessage());
      }
   }
   public static void usingTeeInputStream() throws IOException {
      TeeInputStream teeInputStream = null;
      TeeOutputStream teeOutputStream = null;
      try {
         ByteArrayInputStream inputStream = new ByteArrayInputStream(SAMPLE.getBytes("US-ASCII"));
         ByteArrayOutputStream outputStream1 = new ByteArrayOutputStream();
         ByteArrayOutputStream outputStream2 = new ByteArrayOutputStream();

         teeOutputStream = new TeeOutputStream(outputStream1, outputStream2);
         teeInputStream = new TeeInputStream(inputStream, teeOutputStream, true);
         teeInputStream.read(new byte[SAMPLE.length()]);

         System.out.println("Output stream 1: " + outputStream1.toString());
         System.out.println("Output stream 2: " + outputStream2.toString());

      } catch (IOException e) {
         System.out.println(e.getMessage());
      } finally {
         //teeIn.close() closes teeIn and teeOut which in turn closes the out1 and out2.       
         try { 
            teeInputStream.close(); 
         }
         catch (IOException e) { 
            System.out.println(e.getMessage());
         }
      }
   }
}
It will print the following result.
Output stream 1: Welcome to TutorialsPoint. Simply Easy Learning.
Output stream 2: Welcome to TutorialsPoint. Simply Easy Learning.

TeeOutputStream splits OutputStream. It is named after the unix 'tee' command. It allows a stream to be branched to two streams.
Following is the declaration for org.apache.commons.io.output.TeeOutputStream Class -
public class TeeOutputStream
   extends ProxyOutputStream
In this example, TeeOutputStream accepts two output streams as parameter and passing data to TeeOutputStream set data to both output streams.
IOTester.java
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

import org.apache.commons.io.input.TeeInputStream;
import org.apache.commons.io.output.TeeOutputStream;

public class IOTester {
   private static final String SAMPLE = "Welcome to TutorialsPoint. Simply Easy Learning.";
   public static void main(String[] args) {
      try{
         usingTeeInputStream();
      }catch(IOException e){
         System.out.println(e.getMessage());
      }
   }
   public static void usingTeeInputStream() throws IOException {
      TeeInputStream teeInputStream = null;
      TeeOutputStream teeOutputStream = null;
      try {
         ByteArrayInputStream inputStream = new ByteArrayInputStream(SAMPLE.getBytes("US-ASCII"));
         ByteArrayOutputStream outputStream1 = new ByteArrayOutputStream();
         ByteArrayOutputStream outputStream2 = new ByteArrayOutputStream();

         teeOutputStream = new TeeOutputStream(outputStream1, outputStream2);
         teeInputStream = new TeeInputStream(inputStream, teeOutputStream, true);
         teeInputStream.read(new byte[SAMPLE.length()]);

         System.out.println("Output stream 1: " + outputStream1.toString());
         System.out.println("Output stream 2: " + outputStream2.toString());

      } catch (IOException e) {
         System.out.println(e.getMessage());
      } finally {
         //teeIn.close() closes teeIn and teeOut which in turn closes the out1 and out2.       
         try { 
            teeInputStream.close(); 
         }
         catch (IOException e) { 
            System.out.println(e.getMessage());
         }
      }
   }
}
It will print the following result.
Output stream 1: Welcome to TutorialsPoint. Simply Easy Learning.
Output stream 2: Welcome to TutorialsPoint. Simply Easy Learning.

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