ByteArrayOutputStream class


                  See  OutputStream class  for descriptions of methods ByteArrayOutputStream uses.  They are:


write( int b )                              Writes a single byte, supplied as the low-order byte in an int.

write( byte[ ] )                           Writes an array of bytes.

write( byte[ ], offset, len )          Writes a portion len of a byte array, beginning at offset

close( )                                     Closes the stream, flushing it first.

flush( )                                     Flushes all associated buffers in a stream without closing it.


plus it adds:


.toByteArray( )                          all below

.toString( ) 

.size( ) 


.reset( )                       



  ByteArrayOutputStream allows you to use write(...) methods to add data to a dynamic byte stream.  You can retrieve the stream's contents in any of three ways:

(1) To retrieve the stream's contents as a byte array use the method toByteArray( )

(2) To retrieve them as a String use toString( ) 

(3) To write them out at any time to another Writer stream use the writeTo(...) method.


  If the contents of a ByteArrayOutputStream stream are sent to a byte array using the toByteArray( ) method, a ByteArrayInputStream can then read the resulting array.   See  CharArrayWriter class  for a complete example of this situation using the similar (but character-oriented) classes CharArrayWriter and CharArrayReader,



  There is no void write( String s ) method under OutputStream, as there is on the character side under Writer.  To write a String to an OutputStream, convert the String to a byte array and write it with the method write( byte[ ] ).  i.e.




try {

                ByteArrayOutputStream baos = new ByteArrayOutputStream( );

                String s = "Hello World";

                baos.write( s.getBytes( ) );                  // convert it and write it in the same statement


catch (IOException e) {   }



  ByteArrayOutputStream adds five methods to those provided by OutputStream.  They are described below:



char[ ]   .toByteArray( )  method


  This code returns a new byte array containing the bytes written to this stream thus far.  It allocates a new array.



import java.util.*;


ByteArrayOutputStream bos = new ByteArrayOutputStream( );

bos.write( 65 );

bos.write( 66 );

bos.write( 67 );

byte[ ] ba = new byte [ bos.size( ) ];

ba = bos.toByteArray( );

System.out.println( "bos is " + bos.size( )  + " long and contains: " + bos );

System.out.print( "Array ba contains: ");

for ( int x = 0; x < ba.length;  x++ ) System.out.print( (char) ba[ x ] );


String  .toString( )  method


  The toString( ) method, overridden from Object, returns a String of the whole ByteArrayOutputStream stream written thus far.  i.e.




try {

ByteArrayOutputStream baos = new ByteArrayOutputStream( );

String s = "Hello World";

byte[ ] b = s.getBytes( );

baos.write( b );

System.out.println( baos.toString( ) );


catch (IOException e) {   }


int  .size( )  method


  This code returns an int containing the number of chars actually written to the ByteArrayOutputStream stream buffer thus far. If the reset( ) method is called, it resets this particular value to zero.




try {

    ByteArrayOutputStream baos= new ByteArrayOutputStream( );

    String s1 = "Hello ";

    String s2 = "World";

    baos.write( s1.getBytes( ) );

    baos.write( s2.getBytes( ) );

    int x;

    x = baos.size( );

    System.out.println(x + " characters written.");                             // prints 11

    baos.reset( );                                                     // reset

    x = baos.size( );

    System.out.println(x + " characters written.");                             // now prints 0 after reset


catch (IOException e) { }



void  .writeTo(OutputStream)  method


   This method writes out to any OutputStream all the chars which were written to the ByteArrayOutputStream thus far. 

The snippet below demonstrates.  It writes half of the alphabet, A through M, to a ByteArrayOutputStream.  It then uses ByteArrayOutputStream's writeTo(...) method to write the digits 1234567890 to the PipedWriter stream after the M.  It then continues writing the rest of the alphabet, N to Z, to the PipedWriter stream.  The result is that 1234567890 appears in the middle of the alphabet in the PipedWriter stream.  The associated PipedReader stream shows this result when it reads the PipedWriter stream for printing.




 ByteArrayOutputStream baos = new ByteArrayOutputStream( );

 PipedInputStream pis  = new PipedInputStream( );


 try {

     PipedOutputStream pos  = new PipedOutputStream( );

     pos.connect(  pis );

     for ( int x = 0;  x < S.length( );  x++ )  {

         if ( x == 13 ) {

             String s2 = "1234567890";

             baos.write( s2.getBytes( ) );


     baos.write( S.getBytes( ), x, 1 );


     baos.writeTo( pos );

     for ( int x = 0;  x < 36;  x++ ) {

         System.out.print( (char) ) );


 } catch (IOException e) {  }



void .reset( )  method


  This method discards everything in the ByteArrayOutputStream stream and resets the size( ) count to zero.  Using reset( ) on an existing stream, so that it can be reused, is faster and more efficient than creating a new one.