Hadoop I/O - Hadoop: The Definitive Guide - page 140

WARNING
In some situations, the byte array returned by the getBytes() method may be longer than the length
returned by getLength() :
Text t = new Text ( "hadoop" );
t . set ( new Text ( "pig" ) );
assertThat ( t . getLength (), is ( 3 ));
assertThat ( "Byte length not shortened" , t . getBytes (). length ,
is ( 6 ) );
This shows why it is imperative that you always call getLength() when calling getBytes() , so
you know how much of the byte array is valid data.
Resorting to String
Text doesn't have as rich an API for manipulating strings as java.lang.String , so
in many cases, you need to convert the Text object to a String . This is done in the
usual way, using the toString() method:
assertThat ( new Text ( "hadoop" ). toString (), is ( "hadoop" ));
BytesWritable
BytesWritable is a wrapper for an array of binary data. Its serialized format is a
4-byte integer field that specifies the number of bytes to follow, followed by the bytes
themselves. For example, the byte array of length 2 with values 3 and 5 is serialized as a
4-byte integer ( 00000002 ) followed by the two bytes from the array ( 03 and 05 ):
BytesWritable b = new BytesWritable ( new byte [] { 3 , 5 });
byte [] bytes = serialize ( b );
assertThat ( StringUtils . byteToHexString ( bytes ),
is ( "000000020305" ));
BytesWritable is mutable, and its value may be changed by calling its set() meth-
od. As with Text , the size of the byte array returned from the getBytes() method for
BytesWritable — the capacity — may not reflect the actual size of the data stored in
the BytesWritable . You can determine the size of the BytesWritable by calling
getLength() . To demonstrate:
b . setCapacity ( 11 );
assertThat ( b . getLength (), is ( 2 ));
assertThat ( b . getBytes (). length , is ( 11 ));