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Java.io.FilterInputStream Class in Java - GeeksforGeeks

Last Updated : 23 Jul, 2025

Filter Streams filters data as they read and write data in the Input Stream, filters it and pass it on to the underlying Streams. Filter Streams are

• FilterInputStream
• FilterOutput Stream

class works almost like InputStream class in Java but what it does is simply overriding the InputStream class methods, passing the request to the InputStream. The read() method of FilterInputStream Class filters the data and read it and passes on the data to the underlying stream filtering which is done depending on the Streams.

public class FilterInputStream
   extends InputStream

• protected FilterInputStream(InputStream in): Creates a FilterInputStream by assigning the argument in to the field this.in so as to remember it for later use.

• read(byte[] buffer) : java.io.FilterInputStream.read(byte[] buffer) reads number of bytes of buffer.length from the Filter Input Stream to the buffer array. Syntax :

  public int read(byte[] buffer)
  Parameters :
  buffer : buffer to be read
  Return : 
  reads number of bytes of buffer.length to the buffer 
  else, -1 i.e. when end of file is reached.
  Exception :
  ->  IOException : If I/O error occurs.

Implementation : Java

// Java program illustrating the working of read(byte[] buffer) method

import java.io.*;

public class NewClass
{
    public static void main(String[] args) throws IOException
    {
        // LineNumberInputStream & FileInputStream initailly null
        FilterInputStream geek_input = null;
        InputStream geek = null;

        try{
            char c;
            int a;
            byte[] buffer = new byte[6];

            // New InputStream : 'GEEKS' is created
            geek = new FileInputStream("GEEKS.txt");
            geek_input = new BufferedInputStream(geek);

            a = geek.read(buffer);
            // read() method returning Bytes of Input Stream as integer
            // '-1' indicating to read till end Of Input Stream
            int length = 1 ;
            
            for(byte g : buffer)
            {
                // Since read() method returns Integer value
                // So, we convert each integer value to char
                c = (char)g;

                System.out.println("At position " + length  +  " : "  + c);
                length++;
            }
        }
        catch(Exception e)
        {
            // In case of error
            e.printStackTrace();
            System.out.println("ERROR Occurs ");
        }
        finally
        {
            // Closing the streams, Once the End of Input Stream is reached
            if(geek != null)
                geek.close();

            if(geek_input != null)
                geek_input.close();
        }
    }
}

Note : The following Java Code won’t run here as we can’t access any file on online IDE. So, copy the program to your system and run it there. The GEEKS.txt file used in the program contains :

HelloGeeks

In the given code buffer.length = 6 , So only HelloG will b read by read(byte[] buffer) method Output :

At position 1 : H
At position 2 : e
At position 3 : l
At position 4 : l
At position 5 : o
At position 6 : G

• read(byte[] buffer, int offset, int maxlen) : java.io.FilterInputStream.read(byte[] buffer, int offset, int maxlen) reads upto maxlen of data from the FilterInputStream into a buffer. Syntax :

  public int read(byte[] buffer, int offset, int maxlen)
  Parameters :
  buffer : Destination buffer
  offset : start position to read
  maxlen : max. length of bytes to be read
  Return : 
  total no. of bytes to be written else, -1 i.e. when end of Stream is reached.
  Exception :
  ->  IOException : If I/O error occurs.

Implementation : Java

// Java program illustrating the working of
// read(byte[] buffer, int offset, int maxlen) method

import java.io.*;

public class NewClass
{
    public static void main(String[] args) throws IOException
    {
        // LineNumberInputStream & FileInputStream initailly null
        FilterInputStream geek_input = null;
        InputStream geek = null;

        try{
            char c;
            int a;
            byte[] buffer = new byte[4];

            // New InputStream : 'ABC' is created
            geek = new FileInputStream("ABC.txt");
            geek_input = new BufferedInputStream(geek);

            // Offset = 1(*), Maxlen = 3 (MOH)
            a = geek.read(buffer, 1, 3);
            // read() method returning Bytes of Input Stream as integer
            // '-1' indicating to read till end Of Input Stream
           
            for(byte g : buffer)
            {
                // Since read() method returns Integer value
                // So, we convert each integer value to char
                c = (char)g;

                if(g == 0)
                    c = '*';

                System.out.print(c);
            }
        }
        catch(Exception e)
        {
            // In case of error
            e.printStackTrace();
            System.out.println("ERROR Occurs ");
        }
        finally
        {
            // Closing the streams, Once the End of Input Stream is reached
            if(geek != null)
                geek.close();

            if(geek_input != null)
                geek_input.close();
        }
    }
}

Note : The following Java Code won’t run here as we can’t access any file on online IDE. So, copy the program to your system and run it there. The ABC.txt file used in the program contains :

MOHIT

Offset = 1 i.e. * and Maxlen = 3 i.e. MOH Output :

*MOH

• available() : java.io.FilterInputStream.available() returns the no. of bytes that can be read from the Input Stream. Syntax :

  public int available()
  Parameters : 
  -------
  Return : 
  returns the no. of bytes that can be read from the FilterInputStream.
  Exception: 
  IOException : in case I/O error occurs

Implementation : Java

// Java program illustrating the working of available() method

import java.io.*;
public class NewClass
{
    public static void main(String[] args) throws IOException
    {
        // FilterInputStream & FileInputStream initailly null
        FilterInputStream geek_input = null;

        InputStream geek = null;

        try{
            char c;
            int a, b;

            // New InputStream : 'ABC' is created
            geek = new FileInputStream("ABC.txt");
            geek_input = new BufferedInputStream(geek);

            while((a = geek_input.read()) != -1)
            {
                // So, we convert each integer value to char
                c = (char)a;

                // Use of available method : return no. of bytes that can be read
                a = geek_input.available();
                System.out.println(c + " Bytes available : " + a);

            }
        }
        catch(Exception e)
        {
            // In case of error
            e.printStackTrace();
            System.out.println("ERROR Occurs ");
        }
        finally
        {
            // Closing the streams, Once the End of FilterInputStream is reached
            if(geek != null)
                geek.close();

            if(geek_input != null)
                geek_input.close();
        }
    }
}

Note : The following Java Code won’t run here as we can’t access any file on online IDE. So, copy the program to your system and run it there. The ABC.txt file used in the program contains :

MOHIT

Output :

M Bytes available : 4
O Bytes available : 3
H Bytes available : 2
I Bytes available : 1
T Bytes available : 0

• read() : java.io.FilterInputStream.read() reads next byte of data from the Filter Input Stream. The value byte is returned in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. Syntax :

  public int read()
  Parameters :
  ------
  Return : 
  Reads next data else, -1 i.e. when end of Stream is reached.
  Exception :
  ->  IOException : If I/O error occurs.

• close() : java.io.FilterInputStream.close() closes the Filter Input Stream and releases system resources associated with this stream to Garbage Collector. Syntax :

  public void close()
  Parameters :
  ------
  Return : 
  void
  Exception :
  ->  IOException : If I/O error occurs.

• mark(int arg) : java.io.FilterInputStream.mark(int arg) marks the current position of the FilterInputStream. It sets readlimit i.e. maximum number of bytes that can be read before mark position becomes invalid. Syntax :

  public void mark(int arg)
  Parameters :
  arg : integer specifying the read limit of the input Stream
  Return : 
  void

• skip() : java.io.FilterInputStream.skip(long arg) skips and discards 'arg' bytes from FilterInputStream data. Syntax :

  public long skip(long arg)
  Parameters : 
  arg : no. of bytes of FilterInputStream data to skip.
  Return : 
  no. of bytes to be skipped
  Exception: 
  IOException : in case I/O error occurs

• reset() : java.io.FilterInputStream.reset() is invoked by mark() method. It repositions the FilterInputStream to the marked position. Syntax :

  public void reset()
  Parameters :
  ----
  Return : 
  void
  Exception :
  ->  IOException : If I/O error occurs.

• markSupported() : java.io.FilterInputStream.markSupported() method tests if this input stream supports the mark and reset methods. The markSupported method of InputStream returns false by default. Syntax :

  public boolean markSupported()
  Parameters :
  -------
  Return : 
  true if input stream supports the mark() and reset() method  else,false

Java Program explaining : markSupported(), close(), reset(), mark(), read(), skip() methods Java

// Java program illustrating the working of FilterInputStream method
// mark(), read(), skip()
// markSupported(), close(), reset()

import java.io.*;

public class NewClass
{
    public static void main(String[] args) throws Exception
    {
        InputStream geek = null;
        // FilterInputStream initialised to null here
        FilterInputStream geek_input = null;
        try {

            geek = new FileInputStream("GEEKS.txt");
            
        geek_input = new BufferedInputStream(geek);

            // read() method : reading and printing Characters
            // one by one
            System.out.println("Char : " + (char)geek_input.read());
            System.out.println("Char : " + (char)geek_input.read());
            System.out.println("Char : " + (char)geek_input.read());

            // mark() : read limiing the 'geek' input stream
            geek_input.mark(0);

            // skip() : it results in redaing of 'e' in G'e'eeks
            geek_input.skip(1);
            System.out.println("skip() method comes to play");
            System.out.println("mark() method comes to play");
            System.out.println("Char : " + (char)geek_input.read());
            System.out.println("Char : " + (char)geek_input.read());
            System.out.println("Char : " + (char)geek_input.read());

            boolean check = geek_input.markSupported();
            if (geek_input.markSupported())
            {
                // reset() method : repositioning the stream to
                // marked positions.
                geek_input.reset();
                System.out.println("reset() invoked");
                System.out.println("Char : " + (char)geek_input.read());
                System.out.println("Char : " + (char)geek_input.read());
            }
            else
                System.out.println("reset() method not supported.");
                System.out.println("geek_input.markSupported() supported" 
                                                + " reset() : " + check);

        }
        catch(Exception excpt)
        {
            // in case of I/O error
            excpt.printStackTrace();
        }
        finally
        {
            // releasing the resources back to the
            // GarbageCollector when closes
            if (geek != null)
            { // Use of close() : closing the file
                // and releasing resources
                geek.close();
            }

            if(geek_input != null)
                geek_input.close();
        }
    }
}

Note : This code won’t run on online IDE as no such file is present here. You can run this code on your System to check the working. GEEKS.txt file used in the code has

HelloGeeks

Output :

Char : H
Char : e
Char : l
skip() method comes to play
mark() method comes to play
Char : o
Char : G
Char : e
reset() invoked
Char : l
Char : o
geek_input.markSupported() supported reset() : true

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