Class MemoryCacheSeekableStream

java.lang.Object

java.io.InputStream

org.apache.xmlgraphics.image.codec.util.SeekableStream

org.apache.xmlgraphics.image.codec.util.MemoryCacheSeekableStream

All Implemented Interfaces:

Closeable, DataInput, 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 Summary

Fields

Modifier and Type	Field	Description
private List	data	A Vector of source sectors.
(package private) boolean	foundEOS	True if we've previously reached the end of the source stream
(package private) int	length	Number of bytes read.
private long	pointer	Position of first unread byte.
private static final int	SECTOR_MASK	A mask to determine the offset within a sector.
private static final int	SECTOR_SHIFT	Log_2 of the sector size.
private static final int	SECTOR_SIZE	The sector size.
private InputStream	src	The source input stream.

Fields inherited from class SeekableStream

markPos

Constructor Summary

Constructors

Constructor	Description
MemoryCacheSeekableStream(InputStream src)	Constructs a MemoryCacheSeekableStream that takes its source data from a regular InputStream.

Method Summary

Modifier and Type	Method	Description
boolean	canSeekBackwards()	Returns true since all MemoryCacheSeekableStream instances support seeking backwards.
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 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 InputStream

available, close, nullInputStream, read, readAllBytes, readNBytes, readNBytes, skip, skipNBytes, transferTo

Methods inherited from class Object

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

Field Details

src

private 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_SIZE

private static final int SECTOR_SIZE

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 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 Details

MemoryCacheSeekableStream

public MemoryCacheSeekableStream(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 Details

readUntil

private long readUntil(long pos)
                throws 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:

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 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:

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 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:

IOException - if an I/O error occurs.