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/*
 * Copyright (c) 1996, 2009, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package java.util.zip;


This class provides support for general purpose compression using the
popular ZLIB compression library. The ZLIB compression library was
initially developed as part of the PNG graphics standard and is not
protected by patents. It is fully described in the specifications at
the java.util.zip
package description.

The following code fragment demonstrates a trivial compression
and decompression of a string using Deflater and
Inflater.

try {
    // Encode a String into bytes
    String inputString = "blahblahblah\u20AC\u20AC";
    byte[] input = inputString.getBytes("UTF-8");
    // Compress the bytes
    byte[] output = new byte[100];
    Deflater compresser = new Deflater();
    compresser.setInput(input);
    compresser.finish();
    int compressedDataLength = compresser.deflate(output);
    // Decompress the bytes
    Inflater decompresser = new Inflater();
    decompresser.setInput(output, 0, compressedDataLength);
    byte[] result = new byte[100];
    int resultLength = decompresser.inflate(result);
    decompresser.end();
    // Decode the bytes into a String
    String outputString = new String(result, 0, resultLength, "UTF-8");
} catch(java.io.UnsupportedEncodingException ex) {
    // handle
} catch (java.util.zip.DataFormatException ex) {
    // handle
}



Author:     David Connelly
See Also:
  • Inflater
/**
 * This class provides support for general purpose compression using the
 * popular ZLIB compression library. The ZLIB compression library was
 * initially developed as part of the PNG graphics standard and is not
 * protected by patents. It is fully described in the specifications at
 * the <a href="package-summary.html#package_description">java.util.zip
 * package description</a>.
 *
 * <p>The following code fragment demonstrates a trivial compression
 * and decompression of a string using <tt>Deflater</tt> and
 * <tt>Inflater</tt>.
 *
 * <blockquote><pre>
 * try {
 *     // Encode a String into bytes
 *     String inputString = "blahblahblah\u20AC\u20AC";
 *     byte[] input = inputString.getBytes("UTF-8");
 *
 *     // Compress the bytes
 *     byte[] output = new byte[100];
 *     Deflater compresser = new Deflater();
 *     compresser.setInput(input);
 *     compresser.finish();
 *     int compressedDataLength = compresser.deflate(output);
 *
 *     // Decompress the bytes
 *     Inflater decompresser = new Inflater();
 *     decompresser.setInput(output, 0, compressedDataLength);
 *     byte[] result = new byte[100];
 *     int resultLength = decompresser.inflate(result);
 *     decompresser.end();
 *
 *     // Decode the bytes into a String
 *     String outputString = new String(result, 0, resultLength, "UTF-8");
 * } catch(java.io.UnsupportedEncodingException ex) {
 *     // handle
 * } catch (java.util.zip.DataFormatException ex) {
 *     // handle
 * }
 * </pre></blockquote>
 *
 * @see         Inflater
 * @author      David Connelly
 */
public
class Deflater {

    private final ZStreamRef zsRef;
    private byte[] buf = new byte[0];
    private int off, len;
    private int level, strategy;
    private boolean setParams;
    private boolean finish, finished;

    
Compression method for the deflate algorithm (the only one currently
supported).

/**
     * Compression method for the deflate algorithm (the only one currently
     * supported).
     */
    public static final int DEFLATED = 8;

    
Compression level for no compression.

/**
     * Compression level for no compression.
     */
    public static final int NO_COMPRESSION = 0;

    
Compression level for fastest compression.

/**
     * Compression level for fastest compression.
     */
    public static final int BEST_SPEED = 1;

    
Compression level for best compression.

/**
     * Compression level for best compression.
     */
    public static final int BEST_COMPRESSION = 9;

    
Default compression level.

/**
     * Default compression level.
     */
    public static final int DEFAULT_COMPRESSION = -1;

    
Compression strategy best used for data consisting mostly of small
values with a somewhat random distribution. Forces more Huffman coding
and less string matching.

/**
     * Compression strategy best used for data consisting mostly of small
     * values with a somewhat random distribution. Forces more Huffman coding
     * and less string matching.
     */
    public static final int FILTERED = 1;

    
Compression strategy for Huffman coding only.

/**
     * Compression strategy for Huffman coding only.
     */
    public static final int HUFFMAN_ONLY = 2;

    
Default compression strategy.

/**
     * Default compression strategy.
     */
    public static final int DEFAULT_STRATEGY = 0;

    static {
        /* Zip library is loaded from System.initializeSystemClass */
        initIDs();
    }

    
Creates a new compressor using the specified compression level.
If 'nowrap' is true then the ZLIB header and checksum fields will
not be used in order to support the compression format used in
both GZIP and PKZIP.

Params:
  • level – the compression level (0-9)
  • nowrap – if true then use GZIP compatible compression
/**
     * Creates a new compressor using the specified compression level.
     * If 'nowrap' is true then the ZLIB header and checksum fields will
     * not be used in order to support the compression format used in
     * both GZIP and PKZIP.
     * @param level the compression level (0-9)
     * @param nowrap if true then use GZIP compatible compression
     */
    public Deflater(int level, boolean nowrap) {
        this.level = level;
        this.strategy = DEFAULT_STRATEGY;
        this.zsRef = new ZStreamRef(init(level, DEFAULT_STRATEGY, nowrap));
    }

    
Creates a new compressor using the specified compression level.
Compressed data will be generated in ZLIB format.

Params:
  • level – the compression level (0-9)
/**
     * Creates a new compressor using the specified compression level.
     * Compressed data will be generated in ZLIB format.
     * @param level the compression level (0-9)
     */
    public Deflater(int level) {
        this(level, false);
    }

    
Creates a new compressor with the default compression level.
Compressed data will be generated in ZLIB format.

/**
     * Creates a new compressor with the default compression level.
     * Compressed data will be generated in ZLIB format.
     */
    public Deflater() {
        this(DEFAULT_COMPRESSION, false);
    }

    
Sets input data for compression. This should be called whenever
needsInput() returns true indicating that more input data is required.

Params:
  • b – the input data bytes
  • off – the start offset of the data
  • len – the length of the data
See Also:
/**
     * Sets input data for compression. This should be called whenever
     * needsInput() returns true indicating that more input data is required.
     * @param b the input data bytes
     * @param off the start offset of the data
     * @param len the length of the data
     * @see Deflater#needsInput
     */
    public void setInput(byte[] b, int off, int len) {
        if (b== null) {
            throw new NullPointerException();
        }
        if (off < 0 || len < 0 || off > b.length - len) {
            throw new ArrayIndexOutOfBoundsException();
        }
        synchronized (zsRef) {
            this.buf = b;
            this.off = off;
            this.len = len;
        }
    }

    
Sets input data for compression. This should be called whenever
needsInput() returns true indicating that more input data is required.

Params:
  • b – the input data bytes
See Also:
/**
     * Sets input data for compression. This should be called whenever
     * needsInput() returns true indicating that more input data is required.
     * @param b the input data bytes
     * @see Deflater#needsInput
     */
    public void setInput(byte[] b) {
        setInput(b, 0, b.length);
    }

    
Sets preset dictionary for compression. A preset dictionary is used
when the history buffer can be predetermined. When the data is later
uncompressed with Inflater.inflate(), Inflater.getAdler() can be called
in order to get the Adler-32 value of the dictionary required for
decompression.

Params:
  • b – the dictionary data bytes
  • off – the start offset of the data
  • len – the length of the data
See Also:
/**
     * Sets preset dictionary for compression. A preset dictionary is used
     * when the history buffer can be predetermined. When the data is later
     * uncompressed with Inflater.inflate(), Inflater.getAdler() can be called
     * in order to get the Adler-32 value of the dictionary required for
     * decompression.
     * @param b the dictionary data bytes
     * @param off the start offset of the data
     * @param len the length of the data
     * @see Inflater#inflate
     * @see Inflater#getAdler
     */
    public void setDictionary(byte[] b, int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        }
        if (off < 0 || len < 0 || off > b.length - len) {
            throw new ArrayIndexOutOfBoundsException();
        }
        synchronized (zsRef) {
            ensureOpen();
            setDictionary(zsRef.address(), b, off, len);
        }
    }

    
Sets preset dictionary for compression. A preset dictionary is used
when the history buffer can be predetermined. When the data is later
uncompressed with Inflater.inflate(), Inflater.getAdler() can be called
in order to get the Adler-32 value of the dictionary required for
decompression.

Params:
  • b – the dictionary data bytes
See Also:
/**
     * Sets preset dictionary for compression. A preset dictionary is used
     * when the history buffer can be predetermined. When the data is later
     * uncompressed with Inflater.inflate(), Inflater.getAdler() can be called
     * in order to get the Adler-32 value of the dictionary required for
     * decompression.
     * @param b the dictionary data bytes
     * @see Inflater#inflate
     * @see Inflater#getAdler
     */
    public void setDictionary(byte[] b) {
        setDictionary(b, 0, b.length);
    }

    
Sets the compression strategy to the specified value.

Params:
  • strategy – the new compression strategy
Throws:
/**
     * Sets the compression strategy to the specified value.
     * @param strategy the new compression strategy
     * @exception IllegalArgumentException if the compression strategy is
     *                                     invalid
     */
    public void setStrategy(int strategy) {
        switch (strategy) {
          case DEFAULT_STRATEGY:
          case FILTERED:
          case HUFFMAN_ONLY:
            break;
          default:
            throw new IllegalArgumentException();
        }
        synchronized (zsRef) {
            if (this.strategy != strategy) {
                this.strategy = strategy;
                setParams = true;
            }
        }
    }

    
Sets the current compression level to the specified value.

Params:
  • level – the new compression level (0-9)
Throws:
/**
     * Sets the current compression level to the specified value.
     * @param level the new compression level (0-9)
     * @exception IllegalArgumentException if the compression level is invalid
     */
    public void setLevel(int level) {
        if ((level < 0 || level > 9) && level != DEFAULT_COMPRESSION) {
            throw new IllegalArgumentException("invalid compression level");
        }
        synchronized (zsRef) {
            if (this.level != level) {
                this.level = level;
                setParams = true;
            }
        }
    }

    
Returns true if the input data buffer is empty and setInput()
should be called in order to provide more input.

Returns:true if the input data buffer is empty and setInput()
should be called in order to provide more input
/**
     * Returns true if the input data buffer is empty and setInput()
     * should be called in order to provide more input.
     * @return true if the input data buffer is empty and setInput()
     * should be called in order to provide more input
     */
    public boolean needsInput() {
        return len <= 0;
    }

    
When called, indicates that compression should end with the current
contents of the input buffer.

/**
     * When called, indicates that compression should end with the current
     * contents of the input buffer.
     */
    public void finish() {
        synchronized (zsRef) {
            finish = true;
        }
    }

    
Returns true if the end of the compressed data output stream has
been reached.

Returns:true if the end of the compressed data output stream has
been reached
/**
     * Returns true if the end of the compressed data output stream has
     * been reached.
     * @return true if the end of the compressed data output stream has
     * been reached
     */
    public boolean finished() {
        synchronized (zsRef) {
            return finished;
        }
    }

    
Fills specified buffer with compressed data. Returns actual number
of bytes of compressed data. A return value of 0 indicates that
needsInput() should be called in order to determine if more input
data is required.

Params:
  • b – the buffer for the compressed data
  • off – the start offset of the data
  • len – the maximum number of bytes of compressed data
Returns:the actual number of bytes of compressed data
/**
     * Fills specified buffer with compressed data. Returns actual number
     * of bytes of compressed data. A return value of 0 indicates that
     * needsInput() should be called in order to determine if more input
     * data is required.
     * @param b the buffer for the compressed data
     * @param off the start offset of the data
     * @param len the maximum number of bytes of compressed data
     * @return the actual number of bytes of compressed data
     */
    public int deflate(byte[] b, int off, int len) {
        if (b == null) {
            throw new NullPointerException();
        }
        if (off < 0 || len < 0 || off > b.length - len) {
            throw new ArrayIndexOutOfBoundsException();
        }
        synchronized (zsRef) {
            return deflateBytes(zsRef.address(), b, off, len);
        }
    }

    
Fills specified buffer with compressed data. Returns actual number
of bytes of compressed data. A return value of 0 indicates that
needsInput() should be called in order to determine if more input
data is required.

Params:
  • b – the buffer for the compressed data
Returns:the actual number of bytes of compressed data
/**
     * Fills specified buffer with compressed data. Returns actual number
     * of bytes of compressed data. A return value of 0 indicates that
     * needsInput() should be called in order to determine if more input
     * data is required.
     * @param b the buffer for the compressed data
     * @return the actual number of bytes of compressed data
     */
    public int deflate(byte[] b) {
        return deflate(b, 0, b.length);
    }

    
Returns the ADLER-32 value of the uncompressed data.

Returns:the ADLER-32 value of the uncompressed data
/**
     * Returns the ADLER-32 value of the uncompressed data.
     * @return the ADLER-32 value of the uncompressed data
     */
    public int getAdler() {
        synchronized (zsRef) {
            ensureOpen();
            return getAdler(zsRef.address());
        }
    }

    
Returns the total number of uncompressed bytes input so far.

Since the number of bytes may be greater than Integer.MAX_VALUE, the getBytesRead() method is now the preferred means of obtaining this information.


Returns:the total number of uncompressed bytes input so far
/**
     * Returns the total number of uncompressed bytes input so far.
     *
     * <p>Since the number of bytes may be greater than
     * Integer.MAX_VALUE, the {@link #getBytesRead()} method is now
     * the preferred means of obtaining this information.</p>
     *
     * @return the total number of uncompressed bytes input so far
     */
    public int getTotalIn() {
        return (int) getBytesRead();
    }

    
Returns the total number of uncompressed bytes input so far.


Returns:the total (non-negative) number of uncompressed bytes input so far
Since:1.5
/**
     * Returns the total number of uncompressed bytes input so far.</p>
     *
     * @return the total (non-negative) number of uncompressed bytes input so far
     * @since 1.5
     */
    public long getBytesRead() {
        synchronized (zsRef) {
            ensureOpen();
            return getBytesRead(zsRef.address());
        }
    }

    
Returns the total number of compressed bytes output so far.

Since the number of bytes may be greater than Integer.MAX_VALUE, the getBytesWritten() method is now the preferred means of obtaining this information.


Returns:the total number of compressed bytes output so far
/**
     * Returns the total number of compressed bytes output so far.
     *
     * <p>Since the number of bytes may be greater than
     * Integer.MAX_VALUE, the {@link #getBytesWritten()} method is now
     * the preferred means of obtaining this information.</p>
     *
     * @return the total number of compressed bytes output so far
     */
    public int getTotalOut() {
        return (int) getBytesWritten();
    }

    
Returns the total number of compressed bytes output so far.


Returns:the total (non-negative) number of compressed bytes output so far
Since:1.5
/**
     * Returns the total number of compressed bytes output so far.</p>
     *
     * @return the total (non-negative) number of compressed bytes output so far
     * @since 1.5
     */
    public long getBytesWritten() {
        synchronized (zsRef) {
            ensureOpen();
            return getBytesWritten(zsRef.address());
        }
    }

    
Resets deflater so that a new set of input data can be processed.
Keeps current compression level and strategy settings.

/**
     * Resets deflater so that a new set of input data can be processed.
     * Keeps current compression level and strategy settings.
     */
    public void reset() {
        synchronized (zsRef) {
            ensureOpen();
            reset(zsRef.address());
            finish = false;
            finished = false;
            off = len = 0;
        }
    }

    
Closes the compressor and discards any unprocessed input.
This method should be called when the compressor is no longer
being used, but will also be called automatically by the
finalize() method. Once this method is called, the behavior
of the Deflater object is undefined.

/**
     * Closes the compressor and discards any unprocessed input.
     * This method should be called when the compressor is no longer
     * being used, but will also be called automatically by the
     * finalize() method. Once this method is called, the behavior
     * of the Deflater object is undefined.
     */
    public void end() {
        synchronized (zsRef) {
            long addr = zsRef.address();
            zsRef.clear();
            if (addr != 0) {
                end(addr);
                buf = null;
            }
        }
    }

    
Closes the compressor when garbage is collected.

/**
     * Closes the compressor when garbage is collected.
     */
    protected void finalize() {
        end();
    }

    private void ensureOpen() {
        assert Thread.holdsLock(zsRef);
        if (zsRef.address() == 0)
            throw new NullPointerException("Deflater has been closed");
    }

    private static native void initIDs();
    private native static long init(int level, int strategy, boolean nowrap);
    private native static void setDictionary(long addr, byte[] b, int off,
                                             int len);
    private native int deflateBytes(long addr, byte[] b, int off, int len);
    private native static int getAdler(long addr);
    private native static long getBytesRead(long addr);
    private native static long getBytesWritten(long addr);
    private native static void reset(long addr);
    private native static void end(long addr);
}