Java IO.pdf - Nguyen Dang Binh

UDP
Byte array input and output streams are commonly used when sending and receiving
UDP data over the Internet. Unlike the more common TCP data, which acts like the
streams I discuss in this book, UDP data arrives in raw packets of bytes, which do
not necessarily have any relation to the previous packet or the next packet. Each
packet is just a group of bytes to be processed in isolation from other packets. Thus,
you may get nothing for several seconds, or even minutes, and then suddenly have a
few hundred numbers to deal with.
In Java, UDP data is sent and received via the java.net.DatagramSocket and
java.net.DatagramPacket classes. The receive() method of the
DatagramSocket class returns its data in a DatagramPacket, which is little more
than a wrapper around a byte array. This byte array can be easily used as the source
of a ByteArrayInputStream . UDP is discussed in more detail in Chapter 9 of my
book Java Network Programming (O'Reilly & Associates, 1997).
8.2.1 Byte Array Input Streams
Java I/O
The ByteArrayInputStream class reads data from a byte array using the methods of
java.io.InputStream :
public class ByteArrayInputStream extends InputStream
There are two ByteArrayInputStream() constructors. Both take a byte array as an
argument. This byte array is the buffer from which data will be read. The first constructor
uses the entire buffer array as an input stream. The second constructor only uses the subarray
of length bytes of buffer starting with the byte at offset.
public ByteArrayInputStream(byte[] buffer)
public ByteArrayInputStream(byte[] buffer, int offset, int length)
Other than these two constructors, the ByteArrayInputStream class just has the usual
read(), available(), close(), mark(), and reset() methods. Byte array input streams do
support marking and resetting up to the full length of the stream. This is relatively
straightforward to implement, because a byte array contains all the data in the stream in
memory at any time. There's no need to implement special buffering as with other kinds of
streams and no need to worry that you'll try to reset further back than the buffer allows.
8.2.2 Byte Array Output Streams
The ByteArrayOutputStream class writes data into the successive components of a byte
array using the methods of java.io.OutputStream :
public class ByteArrayOutputStream extends OutputStream
This class has the following two constructors, plus the usual write(), close(), and flush()
methods:
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