Class MemoryCacheSeekableStream

  • All Implemented Interfaces:
    java.io.Closeable, java.io.DataInput, java.lang.AutoCloseable

    public final class MemoryCacheSeekableStream
    extends SeekableStream
    A subclass of SeekableStream that may be used to wrap a regular InputStream. Seeking backwards is supported by means of an in-memory cache. For greater efficiency, FileCacheSeekableStream should be used in circumstances that allow the creation of a temporary file.

    The mark() and reset() methods are supported.

    This class is not a committed part of the JAI API. It may be removed or changed in future releases of JAI.

    • Field Detail

      • src

        private java.io.InputStream src
        The source input stream.
      • pointer

        private long pointer
        Position of first unread byte.
      • SECTOR_SHIFT

        private static final int SECTOR_SHIFT
        Log_2 of the sector size.
        See Also:
        Constant Field Values
      • SECTOR_MASK

        private static final int SECTOR_MASK
        A mask to determine the offset within a sector.
        See Also:
        Constant Field Values
      • data

        private java.util.List data
        A Vector of source sectors.
      • length

        int length
        Number of bytes read.
      • foundEOS

        boolean foundEOS
        True if we've previously reached the end of the source stream
    • Constructor Detail

      • MemoryCacheSeekableStream

        public MemoryCacheSeekableStream​(java.io.InputStream src)
        Constructs a MemoryCacheSeekableStream that takes its source data from a regular InputStream. Seeking backwards is supported by means of an in-memory cache.
    • Method Detail

      • readUntil

        private long readUntil​(long pos)
                        throws java.io.IOException
        Ensures that at least pos bytes are cached, or the end of the source is reached. The return value is equal to the smaller of pos and the length of the source stream.
        Throws:
        java.io.IOException
      • canSeekBackwards

        public boolean canSeekBackwards()
        Returns true since all MemoryCacheSeekableStream instances support seeking backwards.
        Overrides:
        canSeekBackwards in class SeekableStream
      • getFilePointer

        public long getFilePointer()
        Returns the current offset in this file.
        Specified by:
        getFilePointer in class SeekableStream
        Returns:
        the offset from the beginning of the file, in bytes, at which the next read occurs.
      • seek

        public void seek​(long pos)
                  throws java.io.IOException
        Sets the file-pointer offset, measured from the beginning of this file, at which the next read occurs.
        Specified by:
        seek in class SeekableStream
        Parameters:
        pos - the offset position, measured in bytes from the beginning of the file, at which to set the file pointer.
        Throws:
        java.io.IOException - if pos is less than 0 or if an I/O error occurs.
      • read

        public int read()
                 throws java.io.IOException
        Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.
        Specified by:
        read in class SeekableStream
        Returns:
        the next byte of data, or -1 if the end of the stream is reached.
        Throws:
        java.io.IOException - if an I/O error occurs.
      • read

        public int read​(byte[] b,
                        int off,
                        int len)
                 throws java.io.IOException
        Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read, possibly zero. The number of bytes actually read is returned as an integer.

        This method blocks until input data is available, end of file is detected, or an exception is thrown.

        If b is null, a NullPointerException is thrown.

        If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown.

        If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

        The first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k] through b[off+len-1] unaffected.

        In every case, elements b[0] through b[off] and elements b[off+len] through b[b.length-1] are unaffected.

        If the first byte cannot be read for any reason other than end of file, then an IOException is thrown. In particular, an IOException is thrown if the input stream has been closed.

        Specified by:
        read in class SeekableStream
        Parameters:
        b - the buffer into which the data is read.
        off - the start offset in array b at which the data is written.
        len - the maximum number of bytes to read.
        Returns:
        the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.
        Throws:
        java.io.IOException - if an I/O error occurs.