Class Deflater

java.lang.Object
java.util.zip.Deflater
public class Deflater extends Object
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.

Unless otherwise noted, passing a null argument to a method in this class will cause a NullPointerException to be thrown.

This class deflates sequences of bytes into ZLIB compressed data format. The input byte sequence is provided in either byte array or byte buffer, via one of the setInput() methods. The output byte sequence is written to the output byte array or byte buffer passed to the deflate() methods.

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


// Encode a String into bytes
String inputString = "blahblahblah\u20AC\u20AC";
byte[] input = inputString.getBytes(StandardCharsets.UTF_8);

// Compress the bytes
ByteArrayOutputStream compressedBaos = new ByteArrayOutputStream();
Deflater compressor = new Deflater();
try {
    compressor.setInput(input);
    // Let the compressor know that the complete input
    // has been made available
    compressor.finish();
    // Keep compressing the input till the compressor
    // is finished compressing
    while (!compressor.finished()) {
        // Use some reasonable size for the temporary buffer
        // based on the data being compressed
        byte[] tmpBuffer = new byte[100];
        int numCompressed = compressor.deflate(tmpBuffer);
        // Copy over the compressed bytes from the temporary
        // buffer into the final byte array
        compressedBaos.write(tmpBuffer, 0, numCompressed);
    }
} finally {
    // Release the resources held by the compressor
    compressor.end();
}

// Decompress the bytes
Inflater decompressor = new Inflater();
ByteArrayOutputStream decompressedBaos = new ByteArrayOutputStream();
try {
    byte[] compressed = compressedBaos.toByteArray();
    decompressor.setInput(compressed, 0, compressed.length);
    while (!decompressor.finished()) {
        // Use some reasonable size for the temporary buffer,
        // based on the data being decompressed; in this example,
        // we use a small buffer size
        byte[] tmpBuffer = new byte[100];
        int numDecompressed = 0;
        try {
            numDecompressed = decompressor.inflate(tmpBuffer);
        } catch (DataFormatException dfe) {
            // Handle the exception suitably, in this example
            // we just rethrow it
            throw new RuntimeException(dfe);
        }
        // Copy over the decompressed bytes from the temporary
        // buffer into the final byte array
        decompressedBaos.write(tmpBuffer, 0, numDecompressed);
    }
} finally {
    // Release the resources held by the decompressor
    decompressor.end();
}
// Decode the bytes into a String
String outputString = decompressedBaos.toString(StandardCharsets.UTF_8);
API Note:
To release resources used by this Deflater, the end() method should be called explicitly. Subclasses are responsible for the cleanup of resources acquired by the subclass. Subclasses that override Object.finalize() in order to perform cleanup should be modified to use alternative cleanup mechanisms such as Cleaner and remove the overriding finalize method.
Since:
1.1
See Also:

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    BEST_COMPRESSION
    Compression level for best compression.
    static final int
    BEST_SPEED
    Compression level for fastest compression.
    static final int
    DEFAULT_COMPRESSION
    Default compression level.
    static final int
    DEFAULT_STRATEGY
    Default compression strategy.
    static final int
    DEFLATED
    Compression method for the deflate algorithm (the only one currently supported).
    static final int
    FILTERED
    Compression strategy best used for data consisting mostly of small values with a somewhat random distribution.
    static final int
    FULL_FLUSH
    Compression flush mode used to flush out all pending output and reset the deflater.
    static final int
    HUFFMAN_ONLY
    Compression strategy for Huffman coding only.
    static final int
    NO_COMPRESSION
    Compression level for no compression.
    static final int
    NO_FLUSH
    Compression flush mode used to achieve best compression result.
    static final int
    SYNC_FLUSH
    Compression flush mode used to flush out all pending output; may degrade compression for some compression algorithms.

  • Constructor Summary

    Constructors
    Constructor
    Description
    Deflater()
    Creates a new compressor with the default compression level.
    Deflater(int level)
    Creates a new compressor using the specified compression level.
    Deflater(int level, boolean nowrap)
    Creates a new compressor using the specified compression level.

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    deflate(byte[] output)
    Compresses the input data and fills specified buffer with compressed data.
    int
    deflate(byte[] output, int off, int len)
    Compresses the input data and fills specified buffer with compressed data.
    int
    deflate(byte[] output, int off, int len, int flush)
    Compresses the input data and fills the specified buffer with compressed data.
    int
    deflate(ByteBuffer output)
    Compresses the input data and fills specified buffer with compressed data.
    int
    deflate(ByteBuffer output, int flush)
    Compresses the input data and fills the specified buffer with compressed data.
    void
    end()
    Closes the compressor and discards any unprocessed input.
    void
    finish()
    When called, indicates that compression should end with the current contents of the input buffer.
    boolean
    finished()
    Returns true if the end of the compressed data output stream has been reached.
    int
    getAdler()
    Returns the ADLER-32 value of the uncompressed data.
    long
    getBytesRead()
    Returns the total number of uncompressed bytes input so far.
    long
    getBytesWritten()
    Returns the total number of compressed bytes output so far.
    int
    getTotalIn()
    Deprecated.
    Use getBytesRead() instead
    int
    getTotalOut()
    Deprecated.
    Use getBytesWritten() instead
    boolean
    needsInput()
    Returns true if no data remains in the input buffer.
    void
    reset()
    Resets deflater so that a new set of input data can be processed.
    void
    setDictionary(byte[] dictionary)
    Sets preset dictionary for compression.
    void
    setDictionary(byte[] dictionary, int off, int len)
    Sets preset dictionary for compression.
    void
    setDictionary(ByteBuffer dictionary)
    Sets preset dictionary for compression.
    void
    setInput(byte[] input)
    Sets input data for compression.
    void
    setInput(byte[] input, int off, int len)
    Sets input data for compression.
    void
    setInput(ByteBuffer input)
    Sets input data for compression.
    void
    setLevel(int level)
    Sets the compression level to the specified value.
    void
    setStrategy(int strategy)
    Sets the compression strategy to the specified value.

    Methods declared in class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • DEFLATED

      public static final int DEFLATED
      Compression method for the deflate algorithm (the only one currently supported).
      See Also:

    • NO_COMPRESSION

      public static final int NO_COMPRESSION
      Compression level for no compression.
      See Also:

    • BEST_SPEED

      public static final int BEST_SPEED
      Compression level for fastest compression.
      See Also:

    • BEST_COMPRESSION

      public static final int BEST_COMPRESSION
      Compression level for best compression.
      See Also:

    • DEFAULT_COMPRESSION

      public static final int DEFAULT_COMPRESSION
      Default compression level.
      See Also:

    • FILTERED

      public static final int FILTERED
      Compression strategy best used for data consisting mostly of small values with a somewhat random distribution. Forces more Huffman coding and less string matching.
      See Also:

    • HUFFMAN_ONLY

      public static final int HUFFMAN_ONLY
      Compression strategy for Huffman coding only.
      See Also:

    • DEFAULT_STRATEGY

      public static final int DEFAULT_STRATEGY
      Default compression strategy.
      See Also:

    • NO_FLUSH

      public static final int NO_FLUSH
      Compression flush mode used to achieve best compression result.
      Since:
      1.7
      See Also:

    • SYNC_FLUSH

      public static final int SYNC_FLUSH
      Compression flush mode used to flush out all pending output; may degrade compression for some compression algorithms.
      Since:
      1.7
      See Also:

    • FULL_FLUSH

      public static final int FULL_FLUSH
      Compression flush mode used to flush out all pending output and reset the deflater. Using this mode too often can seriously degrade compression.
      Since:
      1.7
      See Also:

  • Constructor Details

    • Deflater

      public Deflater(int level, boolean nowrap)
      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.
      Parameters:
      level - the compression level (0-9)
      nowrap - if true then use GZIP compatible compression

    • Deflater

      public Deflater(int level)
      Creates a new compressor using the specified compression level. Compressed data will be generated in ZLIB format.
      Parameters:
      level - the compression level (0-9)

    • Deflater

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

  • Method Details

    • setInput

      public void setInput(byte[] input, int off, int len)
      Sets input data for compression.

      One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

      Parameters:
      input - the input data bytes
      off - the start offset of the data
      len - the length of the data
      See Also:

    • setInput

      public void setInput(byte[] input)
      Sets input data for compression.

      One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

      Parameters:
      input - the input data bytes
      See Also:

    • setInput

      public void setInput(ByteBuffer input)
      Sets input data for compression.

      One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

      The given buffer's position will be advanced as deflate operations are performed, up to the buffer's limit. The input buffer may be modified (refilled) between deflate operations; doing so is equivalent to creating a new buffer and setting it with this method.

      Modifying the input buffer's contents, position, or limit concurrently with an deflate operation will result in undefined behavior, which may include incorrect operation results or operation failure.

      Parameters:
      input - the input data bytes
      Since:
      11
      See Also:

    • setDictionary

      public void setDictionary(byte[] dictionary, int off, int 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.
      Parameters:
      dictionary - the dictionary data bytes
      off - the start offset of the data
      len - the length of the data
      See Also:

    • setDictionary

      public void setDictionary(byte[] dictionary)
      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.
      Parameters:
      dictionary - the dictionary data bytes
      See Also:

    • setDictionary

      public void setDictionary(ByteBuffer dictionary)
      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.

      The bytes in given byte buffer will be fully consumed by this method. On return, its position will equal its limit.

      Parameters:
      dictionary - the dictionary data bytes
      Since:
      11
      See Also:

    • setStrategy

      public void setStrategy(int strategy)
      Sets the compression strategy to the specified value.

      If the compression strategy is changed, the next invocation of deflate will compress the input available so far with the old strategy (and may be flushed); the new strategy will take effect only after that invocation.

      Parameters:
      strategy - the new compression strategy
      Throws:
      IllegalArgumentException - if the compression strategy is invalid

    • setLevel

      public void setLevel(int level)
      Sets the compression level to the specified value.

      If the compression level is changed, the next invocation of deflate will compress the input available so far with the old level (and may be flushed); the new level will take effect only after that invocation.

      Parameters:
      level - the new compression level (0-9)
      Throws:
      IllegalArgumentException - if the compression level is invalid

    • needsInput

      public boolean needsInput()
      Returns true if no data remains in the input buffer. This can be used to determine if one of the setInput() methods 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

    • finish

      public void finish()
      When called, indicates that compression should end with the current contents of the input buffer.

    • finished

      public boolean finished()
      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

    • deflate

      public int deflate(byte[] output, int off, int len)
      Compresses the input data and 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.

      This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(b, off, len) yields the same result as the invocation of deflater.deflate(b, off, len, Deflater.NO_FLUSH).

      Parameters:
      output - 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 written to the output buffer

    • deflate

      public int deflate(byte[] output)
      Compresses the input data and 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.

      This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(b) yields the same result as the invocation of deflater.deflate(b, 0, b.length, Deflater.NO_FLUSH).

      Parameters:
      output - the buffer for the compressed data
      Returns:
      the actual number of bytes of compressed data written to the output buffer

    • deflate

      public int deflate(ByteBuffer output)
      Compresses the input data and 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.

      This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(output) yields the same result as the invocation of deflater.deflate(output, Deflater.NO_FLUSH).

      Parameters:
      output - the buffer for the compressed data
      Returns:
      the actual number of bytes of compressed data written to the output buffer
      Throws:
      ReadOnlyBufferException - if the given output buffer is read-only
      Since:
      11

    • deflate

      public int deflate(byte[] output, int off, int len, int flush)
      Compresses the input data and fills the specified buffer with compressed data. Returns actual number of bytes of data compressed.

      Compression flush mode is one of the following three modes:

      • NO_FLUSH: allows the deflater to decide how much data to accumulate, before producing output, in order to achieve the best compression (should be used in normal use scenario). A return value of 0 in this flush mode indicates that needsInput() should be called in order to determine if more input data is required.
      • SYNC_FLUSH: all pending output in the deflater is flushed, to the specified output buffer, so that an inflater that works on compressed data can get all input data available so far (In particular the needsInput() returns true after this invocation if enough output space is provided). Flushing with SYNC_FLUSH may degrade compression for some compression algorithms and so it should be used only when necessary.
      • FULL_FLUSH: all pending output is flushed out as with SYNC_FLUSH. The compression state is reset so that the inflater that works on the compressed output data can restart from this point if previous compressed data has been damaged or if random access is desired. Using FULL_FLUSH too often can seriously degrade compression.

      In the case of FULL_FLUSH or SYNC_FLUSH, if the return value is len, the space available in output buffer b, this method should be invoked again with the same flush parameter and more output space. Make sure that len is greater than 6 to avoid flush marker (5 bytes) being repeatedly output to the output buffer every time this method is invoked.

      If the setInput(ByteBuffer) method was called to provide a buffer for input, the input buffer's position will be advanced by the number of bytes consumed by this operation.

      Parameters:
      output - the buffer for the compressed data
      off - the start offset of the data
      len - the maximum number of bytes of compressed data
      flush - the compression flush mode
      Returns:
      the actual number of bytes of compressed data written to the output buffer
      Throws:
      IllegalArgumentException - if the flush mode is invalid
      Since:
      1.7

    • deflate

      public int deflate(ByteBuffer output, int flush)
      Compresses the input data and fills the specified buffer with compressed data. Returns actual number of bytes of data compressed.

      Compression flush mode is one of the following three modes:

      • NO_FLUSH: allows the deflater to decide how much data to accumulate, before producing output, in order to achieve the best compression (should be used in normal use scenario). A return value of 0 in this flush mode indicates that needsInput() should be called in order to determine if more input data is required.
      • SYNC_FLUSH: all pending output in the deflater is flushed, to the specified output buffer, so that an inflater that works on compressed data can get all input data available so far (In particular the needsInput() returns true after this invocation if enough output space is provided). Flushing with SYNC_FLUSH may degrade compression for some compression algorithms and so it should be used only when necessary.
      • FULL_FLUSH: all pending output is flushed out as with SYNC_FLUSH. The compression state is reset so that the inflater that works on the compressed output data can restart from this point if previous compressed data has been damaged or if random access is desired. Using FULL_FLUSH too often can seriously degrade compression.

      In the case of FULL_FLUSH or SYNC_FLUSH, if the return value is equal to the remaining space of the buffer, this method should be invoked again with the same flush parameter and more output space. Make sure that the buffer has at least 6 bytes of remaining space to avoid the flush marker (5 bytes) being repeatedly output to the output buffer every time this method is invoked.

      On success, the position of the given output byte buffer will be advanced by as many bytes as were produced by the operation, which is equal to the number returned by this method.

      If the setInput(ByteBuffer) method was called to provide a buffer for input, the input buffer's position will be advanced by the number of bytes consumed by this operation.

      Parameters:
      output - the buffer for the compressed data
      flush - the compression flush mode
      Returns:
      the actual number of bytes of compressed data written to the output buffer
      Throws:
      IllegalArgumentException - if the flush mode is invalid
      ReadOnlyBufferException - if the given output buffer is read-only
      Since:
      11

    • getAdler

      public int getAdler()
      Returns the ADLER-32 value of the uncompressed data.
      Returns:
      the ADLER-32 value of the uncompressed data

    • getTotalIn

      @Deprecated(since="23") public int getTotalIn()
      Deprecated.
      Use getBytesRead() instead
      Returns the total number of uncompressed bytes input so far.
      Implementation Requirements:
      This method returns the equivalent of (int) getBytesRead() and therefore cannot return the correct value when it is greater than Integer.MAX_VALUE.
      Returns:
      the total number of uncompressed bytes input so far

    • getBytesRead

      public long 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

    • getTotalOut

      @Deprecated(since="23") public int getTotalOut()
      Deprecated.
      Use getBytesWritten() instead
      Returns the total number of compressed bytes output so far.
      Implementation Requirements:
      This method returns the equivalent of (int) getBytesWritten() and therefore cannot return the correct value when it is greater than Integer.MAX_VALUE.
      Returns:
      the total number of compressed bytes output so far

    • getBytesWritten

      public long 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

    • reset

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

    • end

      public void end()
      Closes the compressor and discards any unprocessed input. This method should be called when the compressor is no longer being used. Once this method is called, the behavior of the Deflater object is undefined.