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org.ydp.jai
Class SegmentedSeekableStream  

java.lang.Object
  java.io.InputStream
      org.ydp.jai.SeekableStream
          org.ydp.jai.SegmentedSeekableStream

All Implemented Interfaces:

java.io.Closeable, java.io.DataInput

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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.

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Field Summary
private  boolean	canSeekBackwards
private  StreamSegmentMapper	mapper
private  long	pointer
private  SeekableStream	stream
private  StreamSegment	streamSegment

 

Fields inherited from class org.ydp.jai.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 org.ydp.jai.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

 

Field Detail

stream

private SeekableStream stream

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mapper

private StreamSegmentMapper mapper

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pointer

private long pointer

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canSeekBackwards

private boolean canSeekBackwards

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streamSegment

private StreamSegment streamSegment

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.

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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.

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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.

Method Detail

getFilePointer

public long getFilePointer()

Returns the current offset in this stream.

Specified by:

getFilePointer in class SeekableStream

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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

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seek

public void seek(long pos)
          throws java.io.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

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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

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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 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

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