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org.ydp.jai
Class FileCacheSeekableStream  

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

All Implemented Interfaces:

java.io.Closeable, java.io.DataInput

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public final class FileCacheSeekableStream

extends SeekableStream

A subclass of SeekableStream that may be used to wrap a regular InputStream. Seeking backwards is supported by means of a file cache. In circumstances that do not allow the creation of a temporary file (for example, due to security consideration or the absence of local disk), the MemoryCacheSeekableStream class may be used instead.

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.

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Field Summary
private  byte[]	buf           The read buffer.
private  int	bufLen           The length of the read buffer.
private  java.io.RandomAccessFile	cache           The cache as a RandomAcessFile.
private  java.io.File	cacheFile           The cache File.
private  boolean	foundEOF           True if we've encountered the end of the source stream.
private  long	length           Number of bytes in the cache.
private  long	pointer           Next byte to be read.
private  java.io.InputStream	stream           The source stream.

 

Fields inherited from class org.ydp.jai.SeekableStream

markPos

 

Constructor Summary

FileCacheSeekableStream(java.io.InputStream stream)           Constructs a MemoryCacheSeekableStream that takes its source data from a regular InputStream.

 

Method Summary
boolean	canSeekBackwards()           Returns true since all FileCacheSeekableStream instances support seeking backwards.
void	close()           Closes this stream and releases any system resources associated with the stream.
long	getFilePointer()           Returns the current offset in this file.
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.
private  long	readUntil(long pos)           Ensures that at least pos bytes are cached, or the end of the source is reached.
void	seek(long pos)           Sets the file-pointer offset, measured from the beginning of this file, 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, read, skip

 

Methods inherited from class java.lang.Object

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

 

Field Detail

stream

private java.io.InputStream stream

The source stream.

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cacheFile

private java.io.File cacheFile

The cache File.

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cache

private java.io.RandomAccessFile cache

The cache as a RandomAcessFile.

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bufLen

private int bufLen

The length of the read buffer.

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buf

private byte[] buf

The read buffer.

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length

private long length

Number of bytes in the cache.

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pointer

private long pointer

Next byte to be read.

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foundEOF

private boolean foundEOF

True if we've encountered the end of the source stream.

Constructor Detail

FileCacheSeekableStream

public FileCacheSeekableStream(java.io.InputStream stream)
                        throws java.io.IOException

Constructs a MemoryCacheSeekableStream that takes its source data from a regular InputStream. Seeking backwards is supported by means of an file cache.

An IOException will be thrown if the attempt to create the cache file fails for any reason.

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 file.

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canSeekBackwards

public boolean canSeekBackwards()

Returns true since all FileCacheSeekableStream instances support seeking backwards.

Overrides:

canSeekBackwards in class SeekableStream

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getFilePointer

public long getFilePointer()

Returns the current offset in this file.

Specified by:

getFilePointer in class SeekableStream

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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

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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 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

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close

public void close()
           throws java.io.IOException

Closes this stream and releases any system resources associated with the stream.

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