Deflater (Java Platform SE 8 )
Keywords: java.util.zip.Deflater class
Date: 2026-04-22

compact1, compact2, compact3
java.util.zip

## 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.

  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";
  >          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);
  >          compresser.end();

  >          // 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
  >      }

  See Also:
    `Inflater`

- - ### Field Summary

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

  - ### Constructor Summary

    Constructors
    Constructor and 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

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `deflate(byte[] b)` Compresses the input data and fills specified buffer with compressed data.
    `int` | `deflate(byte[] b, int off, int len)` Compresses the input data and fills specified buffer with compressed data.
    `int` | `deflate(byte[] b, int off, int len, int flush)` Compresses the input data and fills the specified buffer with compressed data.
    `void` | `end()` Closes the compressor and discards any unprocessed input.
    `protected void` | `finalize()` Closes the compressor when garbage is collected.
    `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()` Returns the total number of uncompressed bytes input so far.
    `int` | `getTotalOut()` Returns the total number of compressed bytes output so far.
    `boolean` | `needsInput()` Returns true if the input data buffer is empty and setInput() should be called in order to provide more input.
    `void` | `reset()` Resets deflater so that a new set of input data can be processed.
    `void` | `setDictionary(byte[] b)` Sets preset dictionary for compression.
    `void` | `setDictionary(byte[] b, int off, int len)` Sets preset dictionary for compression.
    `void` | `setInput(byte[] b)` Sets input data for compression.
    `void` | `setInput(byte[] b, int off, int len)` 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 inherited from class java.lang.Object

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

- - ### Field Detail

    - #### DEFLATED

          public static final int DEFLATED

      Compression method for the deflate algorithm (the only one currently supported).
      See Also:
        Constant Field Values

    - #### NO_COMPRESSION

          public static final int NO_COMPRESSION

      Compression level for no compression.
      See Also:
        Constant Field Values

    - #### BEST_SPEED

          public static final int BEST_SPEED

      Compression level for fastest compression.
      See Also:
        Constant Field Values

    - #### BEST_COMPRESSION

          public static final int BEST_COMPRESSION

      Compression level for best compression.
      See Also:
        Constant Field Values

    - #### DEFAULT_COMPRESSION

          public static final int DEFAULT_COMPRESSION

      Default compression level.
      See Also:
        Constant Field Values

    - #### 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:
        Constant Field Values

    - #### HUFFMAN_ONLY

          public static final int HUFFMAN_ONLY

      Compression strategy for Huffman coding only.
      See Also:
        Constant Field Values

    - #### DEFAULT_STRATEGY

          public static final int DEFAULT_STRATEGY

      Default compression strategy.
      See Also:
        Constant Field Values

    - #### NO_FLUSH

          public static final int NO_FLUSH

      Compression flush mode used to achieve best compression result.
      Since:
        1.7
      See Also:
        `deflate(byte[], int, int, int)`, Constant Field Values

    - #### 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:
        `deflate(byte[], int, int, int)`, Constant Field Values

    - #### 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:
        `deflate(byte[], int, int, int)`, Constant Field Values

  - ### Constructor Detail

    - #### 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 Detail

    - #### setInput

          public void setInput(byte[] b,
                               int off,
                               int len)

      Sets input data for compression. This should be called whenever needsInput() returns true indicating that more input data is required.
      Parameters:
        `b` - the input data bytes
        `off` - the start offset of the data
        `len` - the length of the data
      See Also:
        `needsInput()`

    - #### setInput

          public void setInput(byte[] b)

      Sets input data for compression. This should be called whenever needsInput() returns true indicating that more input data is required.
      Parameters:
        `b` - the input data bytes
      See Also:
        `needsInput()`

    - #### setDictionary

          public void setDictionary(byte[] b,
                                    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:
        `b` - the dictionary data bytes
        `off` - the start offset of the data
        `len` - the length of the data
      See Also:
        `Inflater.inflate(byte[], int, int)`, `Inflater.getAdler()`

    - #### setDictionary

          public void setDictionary(byte[] b)

      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:
        `b` - the dictionary data bytes
      See Also:
        `Inflater.inflate(byte[], int, int)`, `Inflater.getAdler()`

    - #### 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 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

    - #### 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[] b,
                             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:
        `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 written to the output buffer

    - #### deflate

          public int deflate(byte[] b)

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

    - #### deflate

          public int deflate(byte[] b,
                             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.

      Parameters:
        `b` - 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

    - #### getAdler

          public int getAdler()

      Returns the ADLER-32 value of the uncompressed data.
      Returns:
        the ADLER-32 value of the uncompressed data

    - #### getTotalIn

          public int getTotalIn()

      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

    - #### 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

          public int getTotalOut()

      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

    - #### 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, but will also be called automatically by the finalize() method. Once this method is called, the behavior of the Deflater object is undefined.

    - #### finalize

          protected void finalize()

      Closes the compressor when garbage is collected.
      Overrides:
        `finalize` in class `Object`
      See Also:
        `WeakReference`, `PhantomReference`

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