Package org.apache.commons.compress.compressors.lzw

Class LZWInputStream

java.lang.Object
java.io.InputStream
org.apache.commons.compress.compressors.CompressorInputStream
org.apache.commons.compress.compressors.lzw.LZWInputStream
All Implemented Interfaces:
Closeable, AutoCloseable, InputStreamStatistics
Direct Known Subclasses:
UnshrinkingInputStream, ZCompressorInputStream
public abstract class LZWInputStream extends CompressorInputStream implements InputStreamStatistics

Generic LZW implementation. It is used internally for the Z decompressor and the Unshrinking Zip file compression method, but may be useful for third-party projects in implementing their own LZW variations.

Since:
1.10

  • Field Details

    • MAX_CODE_SIZE

      private static final int MAX_CODE_SIZE
      Maximum code size in bits.
      See Also:

    • DEFAULT_CODE_SIZE

      protected static final int DEFAULT_CODE_SIZE
      Default code size in bits.
      See Also:

    • UNUSED_PREFIX

      protected static final int UNUSED_PREFIX
      Unused marker.
      See Also:

    • oneByte

      private final byte[] oneByte

    • in

      protected final BitInputStream in
      Input.

    • clearCode

      private int clearCode

    • codeSize

      private int codeSize

    • previousCodeFirstChar

      private byte previousCodeFirstChar

    • previousCode

      private int previousCode

    • tableSize

      private int tableSize

    • prefixes

      private int[] prefixes

    • characters

      private byte[] characters

    • outputStack

      private byte[] outputStack

    • outputStackLocation

      private int outputStackLocation

  • Constructor Details

    • LZWInputStream

      protected LZWInputStream(InputStream inputStream, ByteOrder byteOrder)
      Constructs a new instance.
      Parameters:
      inputStream - The underlying input stream.
      byteOrder - the input byte order.

  • Method Details

    • addEntry

      protected abstract int addEntry(int previousCode, byte character) throws IOException
      Add a new entry to the dictionary.
      Parameters:
      previousCode - the previous code
      character - the next character to append
      Returns:
      the new code
      Throws:
      IOException - on error

    • addEntry

      protected int addEntry(int previousCode, byte character, int maxTableSize)
      Adds a new entry if the maximum table size hasn't been exceeded and returns the new index.
      Parameters:
      previousCode - the previous code
      character - the character to append
      maxTableSize - the maximum table size
      Returns:
      the new code or -1 if maxTableSize has been reached already

    • addRepeatOfPreviousCode

      protected int addRepeatOfPreviousCode() throws IOException
      Add entry for repeat of previousCode we haven't added, yet.
      Returns:
      new code for a repeat of the previous code or -1 if maxTableSize has been reached already
      Throws:
      IOException - on error

    • close

      public void close() throws IOException
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Overrides:
      close in class InputStream
      Throws:
      IOException

    • decompressNextSymbol

      protected abstract int decompressNextSymbol() throws IOException
      Reads the next code and expand it.
      Returns:
      the expanded next code, negative on EOF
      Throws:
      IOException - on error

    • expandCodeToOutputStack

      protected int expandCodeToOutputStack(int code, boolean addedUnfinishedEntry) throws IOException
      Expands the entry with index code to the output stack and may create a new entry.
      Parameters:
      code - the code.
      addedUnfinishedEntry - whether unfinished entries have been added.
      Returns:
      the new location of the output stack.
      Throws:
      IOException - if an I/O error occurs.

    • getClearCode

      protected int getClearCode()
      Gets the clear code.
      Returns:
      the clear code.

    • getCodeSize

      protected int getCodeSize()
      Gets the code size in bits.
      Returns:
      the code size in bits.

    • getCompressedCount

      public long getCompressedCount()
      Description copied from interface: InputStreamStatistics
      Gets the amount of raw or compressed bytes read by the stream.
      Specified by:
      getCompressedCount in interface InputStreamStatistics
      Returns:
      the amount of raw or compressed bytes read by the stream.
      Since:
      1.17

    • getPrefix

      protected int getPrefix(int offset)
      Gets the prefix at the given offset.
      Parameters:
      offset - offset to query.
      Returns:
      the prefix at the given offset.

    • getPrefixesLength

      protected int getPrefixesLength()
      Gets the prefixes length.
      Returns:
      the prefixes length.

    • getTableSize

      protected int getTableSize()
      Gets the table size.
      Returns:
      the table size.

    • incrementCodeSize

      protected void incrementCodeSize()
      Increments the code size by one.

    • initializeTables

      protected void initializeTables(int maxCodeSize)
      Initializes the arrays based on the maximum code size.
      Parameters:
      maxCodeSize - maximum code size
      Throws:
      IllegalArgumentException - if maxCodeSize is out of bounds for prefixes and characters.

    • initializeTables

      protected void initializeTables(int maxCodeSize, int memoryLimiKiB) throws MemoryLimitException
      Initializes the arrays based on the maximum code size. First checks that the estimated memory usage is below memoryLimitInKb
      Parameters:
      maxCodeSize - maximum code size
      memoryLimiKiB - maximum allowed estimated memory usage in kibibytes (KiB).
      Throws:
      MemoryLimitException - if estimated memory usage is greater than memoryLimitKiB
      IllegalArgumentException - if maxCodeSize is not bigger than 0

    • read

      public int read() throws IOException
      Specified by:
      read in class InputStream
      Throws:
      IOException

    • read

      public int read(byte[] b, int off, int len) throws IOException
      Overrides:
      read in class InputStream
      Throws:
      IOException

    • readFromStack

      private int readFromStack(byte[] b, int off, int len)

    • readNextCode

      protected int readNextCode() throws IOException
      Reads the next code from the stream.
      Returns:
      the next code
      Throws:
      IOException - on error

    • resetCodeSize

      protected void resetCodeSize()
      Resets the code size to its default value.

    • resetPreviousCode

      protected void resetPreviousCode()
      Resets the previous code to its default value.

    • setClearCode

      protected void setClearCode(int codeSize)
      Sets the clear code based on the code size.
      Parameters:
      codeSize - code size

    • setCodeSize

      protected void setCodeSize(int codeSize)
      Sets the code size in bits.
      Parameters:
      codeSize - the code size in bits.

    • setPrefix

      protected void setPrefix(int offset, int value)
      Sets the prefix at the given offset.
      Parameters:
      offset - the target offset.
      value - the new value.

    • setTableSize

      protected void setTableSize(int tableSize)
      Sets the table size.
      Parameters:
      tableSize - the new table size.