Java IO.pdf - Nguyen Dang Binh

Java I/O
stream itself, without having to worry about the mechanics of deflation. Similarly, it would be
useful to have an input stream class that could read from a compressed file but return the
uncompressed data. Java, in fact, has several classes that do exactly this. The
java.util.zip.DeflaterOutputStream class is a filter stream that compresses the data it
receives in deflated format before writing it out to the underlying stream. The
java.util.zip.InflaterInputStream class inflates deflated data before passing it to the
reading program. java.util.zip.GZIPInputStream and
java.util.zip.GZIPOutputStream do the same thing except with the gzip format.
9.2.1 The DeflaterOutputStream Class
DeflaterOutputStream is a filter stream that deflates data before writing it onto the
underlying stream:
public class DeflaterOutputStream extends FilterOutputStream
Each stream uses a protected Deflater object called def to compress data stored in a
protected internal buffer called buf:
protected Deflater def;
protected byte[] buf;
The same deflater must not be used in multiple streams at the same time, though Java takes no
steps to guarantee this.
The underlying output stream that receives the deflated data, the deflater object def, and the
length of the byte array buf are all set by one of the three DeflaterOutputStream
constructors:
public DeflaterOutputStream(OutputStream out, Deflater def, int
bufferLength)
public DeflaterOutputStream(OutputStream out, Deflater def)
public DeflaterOutputStream(OutputStream out)
The underlying output stream must be specified. The buffer length defaults to 512 bytes, and
the Deflater defaults to the default compression level, strategy, and method. Of course, the
DeflaterOutputStream has all the usual output stream methods like write(), flush(), and
close(). It overrides three of these methods, but as a client programmer, you don't use them
any differently than you would in any other output stream:
public void write(int b) throws IOException
public void write(byte[] data, int offset, int length) throws IOException
public void close() throws IOException
There's also one new method, finish(), which finishes writing the compressed data onto the
underlying output stream but does not close the underlying stream. You should call finish()
instead of close() if there are multiple filters chained to the stream:
public void finish() throws IOException
The close() method finishes writing the compressed data onto the underlying stream and
then closes it:
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