[Chapter 18] GZIPInputStream

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| 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

## Description

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`

## See Also

`FilterInputStream`, `Inflater`, `InflaterInputStream`, `InputStream`, `IOException`

DeflaterOutputStream |  | GZIPOutputStream