com.sun.media.jai.codec
Class SegmentedSeekableStream

java.lang.Object
  extended byjava.io.InputStream
      extended bycom.sun.media.jai.codec.SeekableStream
          extended bycom.sun.media.jai.codec.SegmentedSeekableStream
All Implemented Interfaces:
DataInput

public class SegmentedSeekableStream
extends SeekableStream

A SegmentedSeekableStream provides a view of a subset of another SeekableStream consiting of a series of segments with given starting positions in the source stream and lengths. The resulting stream behaves like an ordinary SeekableStream.

For example, given a SeekableStream containing data in a format consisting of a number of sub-streams stored in non-contiguous sectors indexed by a directory, it is possible to construct a set of SegmentedSeekableStreams, one for each sub-stream, that each provide a view of the sectors comprising a particular stream by providing the positions and lengths of the stream's sectors as indicated by the directory. The complex multi-stream structure of the original stream may be ignored by users of the SegmentedSeekableStream, who see a separate SeekableStream for each sub-stream and do not need to understand the directory structure at all.

For further efficiency, a directory structure such as in the example described above need not be fully parsed in order to build a SegmentedSeekableStream. Instead, the StreamSegmentMapper interface allows the association between a desired region of the output and an input segment to be provided dynamically. This mapping might be computed by reading from a directory in piecemeal fashion in order to avoid consuming memory resources.

It is the responsibility of the user of this class to determine whether backwards seeking should be enabled. If the source stream supports only forward seeking, backwards seeking must be disabled and the StreamSegmentMapper must be monotone; that is, forward motion in the destination must always result in forward motion within the source. If the source stream supports backwards seeking, there are no restrictions on the StreamSegmentMapper and backwards seeking may always be enabled for the SegmentedSeekableStream.

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


Field Summary
 
Fields inherited from class com.sun.media.jai.codec.SeekableStream
markPos
 
Constructor Summary
SegmentedSeekableStream(SeekableStream stream, long[] segmentPositions, int[] segmentLengths, boolean canSeekBackwards)
          Constructs a SegmentedSeekableStream given a SeekableStream as input, a list of the starting positions and lengths of the segments of the source stream, and a boolean indicating whether the output SegmentedSeekableStream should support seeking backwards.
SegmentedSeekableStream(SeekableStream stream, long[] segmentPositions, int segmentLength, int totalLength, boolean canSeekBackwards)
          Constructs a SegmentedSeekableStream given a SeekableStream as input, a list of the starting positions of the segments of the source stream, the common length of each segment, the total length of the segments and a boolean indicating whether the output SegmentedSeekableStream should support seeking backwards.
SegmentedSeekableStream(SeekableStream stream, StreamSegmentMapper mapper, boolean canSeekBackwards)
          Constructs a SegmentedSeekableStream given a SeekableStream as input, an instance of StreamSegmentMapper, and a boolean indicating whether the output SegmentedSeekableStream should support seeking backwards.
 
Method Summary
 boolean canSeekBackwards()
          Returns true if seeking backwards is supported.
 long getFilePointer()
          Returns the current offset in this stream.
 int read()
          Reads the next byte of data from the input stream.
 int read(byte[] b, int off, int len)
          Reads up to len bytes of data from the input stream into an array of bytes.
 void seek(long pos)
          Sets the offset, measured from the beginning of this stream, at which the next read occurs.
 
Methods inherited from class com.sun.media.jai.codec.SeekableStream
finalize, mark, markSupported, readBoolean, readByte, readChar, readCharLE, readDouble, readDoubleLE, readFloat, readFloatLE, readFully, readFully, readInt, readIntLE, readLine, readLong, readLongLE, readShort, readShortLE, readUnsignedByte, readUnsignedInt, readUnsignedIntLE, readUnsignedShort, readUnsignedShortLE, readUTF, reset, skipBytes, wrapInputStream
 
Methods inherited from class java.io.InputStream
available, close, read, skip
 
Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

SegmentedSeekableStream

public SegmentedSeekableStream(SeekableStream stream,
                               StreamSegmentMapper mapper,
                               boolean canSeekBackwards)
Constructs a SegmentedSeekableStream given a SeekableStream as input, an instance of StreamSegmentMapper, and a boolean indicating whether the output SegmentedSeekableStream should support seeking backwards. If canSeekBackwards is true, the source stream must itself support seeking backwards.

Parameters:
stream - A source SeekableStream
mapper - An instance of the StreamSegmentMapper interface.
canSeekBackwards - true if the ability to seek backwards is desired.

SegmentedSeekableStream

public SegmentedSeekableStream(SeekableStream stream,
                               long[] segmentPositions,
                               int[] segmentLengths,
                               boolean canSeekBackwards)
Constructs a SegmentedSeekableStream given a SeekableStream as input, a list of the starting positions and lengths of the segments of the source stream, and a boolean indicating whether the output SegmentedSeekableStream should support seeking backwards. If canSeekBakckwards is true, the source stream must itself support seeking backwards.

Parameters:
stream - A source SeekableStream
segmentPositions - An array of longs giving the starting positions of the segments in the source stream.
segmentLengths - An array of ints giving the lengths of segments in the source stream.
canSeekBackwards - true if the ability to seek backwards is desired.

SegmentedSeekableStream

public SegmentedSeekableStream(SeekableStream stream,
                               long[] segmentPositions,
                               int segmentLength,
                               int totalLength,
                               boolean canSeekBackwards)
Constructs a SegmentedSeekableStream given a SeekableStream as input, a list of the starting positions of the segments of the source stream, the common length of each segment, the total length of the segments and a boolean indicating whether the output SegmentedSeekableStream should support seeking backwards. If canSeekBakckwards is true, the source stream must itself support seeking backwards.

This constructor is useful for selecting substreams of sector-oriented file formats in which each segment of the substream (except possibly the final segment) occupies a fixed-length sector.

Parameters:
stream - A source SeekableStream
segmentPositions - An array of longs giving the starting positions of the segments in the source stream.
segmentLength - The common length of each segment.
totalLength - The total length of the source segments.
canSeekBackwards - true if the ability to seek backwards is desired.
Method Detail

getFilePointer

public long getFilePointer()
Returns the current offset in this stream.

Specified by:
getFilePointer in class SeekableStream
Returns:
the offset from the beginning of the stream, in bytes, at which the next read occurs.

canSeekBackwards

public boolean canSeekBackwards()
Returns true if seeking backwards is supported. Support is determined by the value of the canSeekBackwards parameter at construction time.

Overrides:
canSeekBackwards in class SeekableStream

seek

public void seek(long pos)
          throws IOException
Sets the offset, measured from the beginning of this stream, at which the next read occurs.

If canSeekBackwards() returns false, then setting pos to an offset smaller than the current value of getFilePointer() will have no effect.

Specified by:
seek in class SeekableStream
Parameters:
pos - the offset position, measured in bytes from the beginning of the stream, at which to set the stream pointer.
Throws:
IOException - if pos is less than 0 or if an I/O error occurs.

read

public int read()
         throws 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:
IOException - if an I/O error occurs.

read

public int read(byte[] b,
                int off,
                int len)
         throws 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 stream 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 stream, 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 stream, 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:
IOException - if an I/O error occurs.