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
FilterInputStream : Java.io.FilterInputStream 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.
Declaration:
public class FilterInputStream extends InputStream
Constructors :
- 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.
Methods:
- 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 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
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 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
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 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
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.
Syntax :
public void close() Parameters : ------ Return : void Exception : -> IOException : If I/O error occurs.
Syntax :
public void mark(int arg) Parameters : arg : integer specifying the read limit of the input Stream Return : void
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
Syntax :
public void reset() Parameters : ---- Return : void Exception : -> IOException : If I/O error occurs.
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 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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