Chapter 18
The java.util.zip Package

GZIPInputStream

Name

GZIPInputStream

Synopsis

Class Name:

java.util.zip.GZIPInputStream

Superclass:

java.util.zip.InflaterInputStream

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

New as of JDK 1.1

The GZIPInputStream class decompresses data that has been compressed using the GZIP format. To use it, simply construct a GZIPInputStream that wraps regular input stream and use the read() methods to read the compressed data.

Class Summary

public class java.util.zip.GZIPInputStream 
             extends java.util.zip.InflaterInputStream {
  // Constants
  public static final int GZIP_MAGIC;
  // Variables
  protected CRC32 crc;
  protected boolean eos;
  // Constructors
  public GZIPInputStream(InputStream in);
  public GZIPInputStream(InputStream in, int size);
  // Instance Methods
  public void close();
  public int read(byte[] buf, int off, int len);
}

Constants

GZIP_MAGIC

public static final int GZIP_MAGIC

Description: A constant that contains the "magic number" that appears in the header of GZIP files.

Variables

crc

protected CRC32 crc

Description: A checksum value of the uncompressed data. When an entire file has been read, this checksum is compared to a value stored in the GZIP trailer. If the values do not match, an exception is thrown from read().

eos

protected boolean eos

Description: A flag that indicates whether or not the end of the compressed stream has been reached. It is set to true when the compressed data and the GZIP trailer have been read.

Constructors

GZIPInputStream

public GZIPInputStream(InputStream in) throws IOException

Parameters

in: The underlying input stream.

Throws

IOException: If an error occurs while reading the GZIP header.

Description

This constructor creates a GZIPInputStream that inflates data from the given InputStream. The GZIPInputStream uses a decompression buffer with the default size of 512 bytes. The GZIP header is read immediately.

 public GZIPInputStream(InputStream in, int size) throws IOException

Parameters

in

The underlying input stream.

size

The size of the input buffer.

Throws

IOException: If an error occurs while reading the GZIP header.

Description

This constructor creates a GZIPInputStream that inflates data from the given InputStream. The GZIPInputStream uses a decompression buffer of the given size. The GZIP header is read immediately.

Instance Methods

close

public void close() throws IOException

Throws

IOException: If any kind of I/O error occurs.

Overrides

FilterInputStream.close()

Description

This method closes this stream and releases any system resources that are associated with it.

read

public int read(byte[] buf, int off, int len) throws IOException

Parameters

buf

An array of bytes to be filled from the stream.

off

An offset into the byte array.

len

The number of bytes to read.

Returns

The number of bytes read or -1 if the end of the stream is encountered immediately.

Throws

IOException: If any kind of I/O error occurs or the checksum of the uncompressed data does not match that in the GZIP trailer.

Overrides

InflaterInputStream.read(byte[], int, int)

Description

This method reads enough data from the underlying InputStream to return len bytes of uncompressed data. The uncompressed data is placed into the given array starting at off. The method blocks until some data is available for decompression.

Inherited Methods

Method	Inherited From	Method	Inherited From
`available()`	`FilterInputStream`	`clone()`	`Object`
`equals(Object)`	`Object`	`finalize()`	`Object`
`getClass()`	`Object`	`hashCode()`	`Object`
`mark(int)`	`FilterInputStream`	`markSupported()`	`FilterInputStream`
`notify()`	`Object`	`notifyAll()`	`Object`
`read()`	`InflaterInputStream`	`read(byte[])`	`FilterInputStream`
`reset()`	`FilterInputStream`	`skip(long)`	`InflaterInputStream`
`toString()`	`Object`	`wait()`	`Object`
`wait(long)`	`Object`	`wait(long, int)`	`Object`