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MemoryCacheImageOutputStream (Java 2 Platform SE 5.0) - JDK 5 Documentation v1.5.0, Java 2 SDK 英文文档

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javax.imageio.stream
Class MemoryCacheImageOutputStream

java.lang.Object
  javax.imageio.stream.ImageInputStreamImpl
      javax.imageio.stream.ImageOutputStreamImpl
          javax.imageio.stream.MemoryCacheImageOutputStream

All Implemented Interfaces:

DataInput, DataOutput, ImageInputStream, ImageOutputStream

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public class MemoryCacheImageOutputStream
extends ImageOutputStreamImpl

An implementation of ImageOutputStream that writes its output to a regular OutputStream. A memory buffer is used to cache at least the data between the discard position and the current write position. The only constructor takes an OutputStream, so this class may not be used for read/modify/write operations. Reading can occur only on parts of the stream that have already been written to the cache and not yet flushed.

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Field Summary

 

Fields inherited from class javax.imageio.stream.ImageInputStreamImpl
bitOffset, byteOrder, flushedPos, streamPos

 

Constructor Summary
MemoryCacheImageOutputStream(OutputStream stream)           Constructs a MemoryCacheImageOutputStream that will write to a given OutputStream.

 

Method Summary
void	close()           Closes this MemoryCacheImageOutputStream.
void	flushBefore(long pos)           Discards the initial portion of the stream prior to the indicated postion.
boolean	isCached()           Returns true since this ImageOutputStream caches data in order to allow seeking backwards.
boolean	isCachedFile()           Returns false since this ImageOutputStream does not maintain a file cache.
boolean	isCachedMemory()           Returns true since this ImageOutputStream maintains a main memory cache.
long	length()           Returns -1L to indicate that the stream has unknown length.
int	read()           Reads a single byte from the stream and returns it as an integer between 0 and 255.
int	read(byte[] b, int off, int len)           Reads up to len bytes from the stream, and stores them into b starting at index off.
void	write(byte[] b, int off, int len)           Writes len bytes from array b, in order, to the output stream.
void	write(int b)           Writes to the output stream the eight low-order bits of the argument b.

 

Methods inherited from class javax.imageio.stream.ImageOutputStreamImpl
flushBits, write, writeBit, writeBits, writeBoolean, writeByte, writeBytes, writeChar, writeChars, writeChars, writeDouble, writeDoubles, writeFloat, writeFloats, writeInt, writeInts, writeLong, writeLongs, writeShort, writeShorts, writeUTF

 

Methods inherited from class javax.imageio.stream.ImageInputStreamImpl

checkClosed, finalize, flush, getBitOffset, getByteOrder, getFlushedPosition, getStreamPosition, mark, read, readBit, readBits, readBoolean, readByte, readBytes, readChar, readDouble, readFloat, readFully, readFully, readFully, readFully, readFully, readFully, readFully, readFully, readInt, readLine, readLong, readShort, readUnsignedByte, readUnsignedInt, readUnsignedShort, readUTF, reset, seek, setBitOffset, setByteOrder, skipBytes, skipBytes

 

Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Methods inherited from interface javax.imageio.stream.ImageInputStream

flush, getBitOffset, getByteOrder, getFlushedPosition, getStreamPosition, mark, read, readBit, readBits, readBoolean, readByte, readBytes, readChar, readDouble, readFloat, readFully, readFully, readFully, readFully, readFully, readFully, readFully, readFully, readInt, readLine, readLong, readShort, readUnsignedByte, readUnsignedInt, readUnsignedShort, readUTF, reset, seek, setBitOffset, setByteOrder, skipBytes, skipBytes

 

Constructor Detail

MemoryCacheImageOutputStream

public MemoryCacheImageOutputStream(OutputStream stream)

Constructs a MemoryCacheImageOutputStream that will write to a given OutputStream.

Parameters:

stream - an OutputStream to write to.

Throws:

IllegalArgumentException - if stream is null.

Method Detail

read

public int read()
         throws IOException

Description copied from interface: ImageInputStream

Reads a single byte from the stream and returns it as an integer between 0 and 255. If the end of the stream is reached, -1 is returned.

The bit offset within the stream is reset to zero before the read occurs.

Specified by:

read in interface ImageInputStream

Specified by:

read in class ImageInputStreamImpl

Returns:

a byte value from the stream, as an int, or -1 to indicate EOF.

Throws:

IOException - if an I/O error occurs.

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read

public int read(byte[] b,
                int off,
                int len)
         throws IOException

Description copied from class: ImageInputStreamImpl

Reads up to len bytes from the stream, and stores them into b starting at index off. If no bytes can be read because the end of the stream has been reached, -1 is returned.

The bit offset within the stream must be reset to zero before the read occurs.

Subclasses must provide an implementation for this method. The subclass implementation should update the stream position before exiting.

Specified by:

read in interface ImageInputStream

Specified by:

read in class ImageInputStreamImpl

Parameters:

b - an array of bytes to be written to.

off - the starting position within b to write to.

len - the maximum number of bytes to read.

Returns:

the number of bytes actually read, or -1 to indicate EOF.

Throws:

IOException - if an I/O error occurs.

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write

public void write(int b)
           throws IOException

Description copied from interface: DataOutput

Writes to the output stream the eight low-order bits of the argument b. The 24 high-order bits of b are ignored.

Specified by:

write in interface DataOutput

Specified by:

write in interface ImageOutputStream

Specified by:

write in class ImageOutputStreamImpl

Parameters:

b - the byte to be written.

Throws:

IOException - if an I/O error occurs.

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write

public void write(byte[] b,
                  int off,
                  int len)
           throws IOException

Description copied from interface: DataOutput

Writes len bytes from array b, in order, to the output stream. 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 written. Otherwise, the byte b[off] is written first, then b[off+1], and so on; the last byte written is b[off+len-1].

Specified by:

write in interface DataOutput

Specified by:

write in interface ImageOutputStream

Specified by:

write in class ImageOutputStreamImpl

Parameters:

b - the data.

off - the start offset in the data.

len - the number of bytes to write.

Throws:

IOException - if an I/O error occurs.

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length

public long length()

Description copied from class: ImageInputStreamImpl

Returns -1L to indicate that the stream has unknown length. Subclasses must override this method to provide actual length information.

Specified by:

length in interface ImageInputStream

Overrides:

length in class ImageInputStreamImpl

Returns:

-1L to indicate unknown length.

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isCached

public boolean isCached()

Returns true since this ImageOutputStream caches data in order to allow seeking backwards.

Specified by:

isCached in interface ImageInputStream

Overrides:

isCached in class ImageInputStreamImpl

Returns:

true.

See Also:

isCachedMemory(), isCachedFile()

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isCachedFile

public boolean isCachedFile()

Returns false since this ImageOutputStream does not maintain a file cache.

Specified by:

isCachedFile in interface ImageInputStream

Overrides:

isCachedFile in class ImageInputStreamImpl

Returns:

false.

See Also:

isCached(), isCachedMemory()

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isCachedMemory

public boolean isCachedMemory()

Returns true since this ImageOutputStream maintains a main memory cache.

Specified by:

isCachedMemory in interface ImageInputStream

Overrides:

isCachedMemory in class ImageInputStreamImpl

Returns:

true.

See Also:

isCached(), isCachedFile()

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close

public void close()
           throws IOException

Closes this MemoryCacheImageOutputStream. All pending data is flushed to the output, and the cache is released. The destination OutputStream is not closed.

Specified by:

close in interface ImageInputStream

Overrides:

close in class ImageInputStreamImpl

Throws:

IOException - if an I/O error occurs.

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flushBefore

public void flushBefore(long pos)
                 throws IOException

Description copied from interface: ImageInputStream

Discards the initial portion of the stream prior to the indicated postion. Attempting to seek to an offset within the flushed portion of the stream will result in an IndexOutOfBoundsException.

Calling flushBefore may allow classes implementing this interface to free up resources such as memory or disk space that are being used to store data from the stream.

Specified by:

flushBefore in interface ImageInputStream

Specified by:

flushBefore in interface ImageOutputStream

Overrides:

flushBefore in class ImageInputStreamImpl

Parameters:

pos - a long containing the length of the file prefix that may be flushed.

Throws:

IOException - if an I/O error occurs.

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