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

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Java^TM 2 Platform
Standard Ed. 5.0

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javax.imageio.stream
Class ImageInputStreamImpl

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

All Implemented Interfaces:: DataInput, ImageInputStream

Direct Known Subclasses:: FileCacheImageInputStream, FileImageInputStream, ImageOutputStreamImpl, MemoryCacheImageInputStream

public abstract class ImageInputStreamImpl
extends Object
implements ImageInputStream
extends Object
implements ImageInputStream

An abstract class implementing the ImageInputStream interface. This class is designed to reduce the number of methods that must be implemented by subclasses.

In particular, this class handles most or all of the details of byte order interpretation, buffering, mark/reset, discarding, closing, and disposing.

Field Summary

protected int bitOffset
          The current bit offset within the stream.

protected ByteOrder byteOrder
          The byte order of the stream as an instance of the enumeration class java.nio.ByteOrder, where ByteOrder.BIG_ENDIAN indicates network byte order and ByteOrder.LITTLE_ENDIAN indicates the reverse order.

protected long flushedPos
          The position prior to which data may be discarded.

protected long streamPos
          The current read position within the stream.

Constructor Summary

ImageInputStreamImpl()
          Constructs an ImageInputStreamImpl.

Method Summary

protected void checkClosed()
          Throws an IOException if the stream has been closed.

void close()
          Closes the stream.

protected void finalize()
          Finalizes this object prior to garbage collection.

void flush()
          Discards the initial position of the stream prior to the current stream position.

void flushBefore(long pos)
          Discards the initial portion of the stream prior to the indicated postion.

int getBitOffset()
          Returns the current bit offset, as an integer between 0 and 7, inclusive.

ByteOrder getByteOrder()
          Returns the byte order with which data values will be read from this stream as an instance of the java.nio.ByteOrder enumeration.

long getFlushedPosition()
          Returns the earliest position in the stream to which seeking may be performed.

long getStreamPosition()
          Returns the current byte position of the stream.

boolean isCached()
          Default implementation returns false.

boolean isCachedFile()
          Default implementation returns false.

boolean isCachedMemory()
          Default implementation returns false.

long length()
          Returns -1L to indicate that the stream has unknown length.

void mark()
          Pushes the current stream position onto a stack of marked positions.

abstract int read()
          Reads a single byte from the stream and returns it as an integer between 0 and 255.

int read(byte[] b)
          A convenience method that calls read(b, 0, b.length).

abstract 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.

int readBit()
          Reads a single bit from the stream and returns it as an int with the value 0 or 1.

long readBits(int numBits)
          Reads a bitstring from the stream and returns it as a long, with the first bit read becoming the most significant bit of the output.

boolean readBoolean()
          Reads one input byte and returns true if that byte is nonzero, false if that byte is zero.

byte readByte()
          Reads and returns one input byte.

void readBytes(IIOByteBuffer buf, int len)
          Reads up to len bytes from the stream, and modifies the supplied IIOByteBuffer to indicate the byte array, offset, and length where the data may be found.

char readChar()
          Reads an input char and returns the char value.

double readDouble()
          Reads eight input bytes and returns a double value.

float readFloat()
          Reads four input bytes and returns a float value.

void readFully(byte[] b)
          Reads some bytes from an input stream and stores them into the buffer array b.

void readFully(byte[] b, int off, int len)
          Reads len bytes from an input stream.

void readFully(char[] c, int off, int len)
          Reads len chars (unsigned 16-bit integers) from the stream according to the current byte order, and stores them into c starting at index off.

void readFully(double[] d, int off, int len)
          Reads len doubles (64-bit IEEE double-precision floats) from the stream according to the current byte order, and stores them into d starting at index off.

void readFully(float[] f, int off, int len)
          Reads len floats (32-bit IEEE single-precision floats) from the stream according to the current byte order, and stores them into f starting at index off.

void readFully(int[] i, int off, int len)
          Reads len ints (signed 32-bit integers) from the stream according to the current byte order, and stores them into i starting at index off.

void readFully(long[] l, int off, int len)
          Reads len longs (signed 64-bit integers) from the stream according to the current byte order, and stores them into l starting at index off.

void readFully(short[] s, int off, int len)
          Reads len shorts (signed 16-bit integers) from the stream according to the current byte order, and stores them into s starting at index off.

int readInt()
          Reads four input bytes and returns an int value.

String readLine()
          Reads the next line of text from the input stream.

long readLong()
          Reads eight input bytes and returns a long value.

short readShort()
          Reads two input bytes and returns a short value.

int readUnsignedByte()
          Reads one input byte, zero-extends it to type int, and returns the result, which is therefore in the range 0 through 255.

long readUnsignedInt()
          Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order, converts the result to a long, masks it with 0xffffffffL in order to strip off any sign-extension bits, and returns the result as an unsigned long value.

int readUnsignedShort()
          Reads two input bytes and returns an int value in the range 0 through 65535.

String readUTF()
          Reads in a string that has been encoded using a modified UTF-8 format.

void reset()
          Resets the current stream byte and bit positions from the stack of marked positions.

void seek(long pos)
          Sets the current stream position to the desired location.

void setBitOffset(int bitOffset)
          Sets the bit offset to an integer between 0 and 7, inclusive.

void setByteOrder(ByteOrder byteOrder)
          Sets the desired byte order for future reads of data values from this stream.

int skipBytes(int n)
          Advances the current stream position by calling seek(getStreamPosition() + n).

long skipBytes(long n)
          Advances the current stream position by calling seek(getStreamPosition() + n).

Methods inherited from class java.lang.Object

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

Field Summary
`protected int`	`bitOffset` The current bit offset within the stream.
`protected ByteOrder`	`byteOrder` The byte order of the stream as an instance of the enumeration class `java.nio.ByteOrder`, where `ByteOrder.BIG_ENDIAN` indicates network byte order and `ByteOrder.LITTLE_ENDIAN` indicates the reverse order.
`protected long`	`flushedPos` The position prior to which data may be discarded.
`protected long`	`streamPos` The current read position within the stream.

Constructor Summary
`ImageInputStreamImpl()` Constructs an `ImageInputStreamImpl`.

Method Summary
`protected void`	`checkClosed()` Throws an `IOException` if the stream has been closed.
`void`	`close()` Closes the stream.
`protected void`	`finalize()` Finalizes this object prior to garbage collection.
`void`	`flush()` Discards the initial position of the stream prior to the current stream position.
`void`	`flushBefore(long pos)` Discards the initial portion of the stream prior to the indicated postion.
`int`	`getBitOffset()` Returns the current bit offset, as an integer between 0 and 7, inclusive.
`ByteOrder`	`getByteOrder()` Returns the byte order with which data values will be read from this stream as an instance of the `java.nio.ByteOrder` enumeration.
`long`	`getFlushedPosition()` Returns the earliest position in the stream to which seeking may be performed.
`long`	`getStreamPosition()` Returns the current byte position of the stream.
`boolean`	`isCached()` Default implementation returns false.
`boolean`	`isCachedFile()` Default implementation returns false.
`boolean`	`isCachedMemory()` Default implementation returns false.
`long`	`length()` Returns `-1L` to indicate that the stream has unknown length.
`void`	`mark()` Pushes the current stream position onto a stack of marked positions.
`abstract int`	`read()` Reads a single byte from the stream and returns it as an integer between 0 and 255.
`int`	`read(byte[] b)` A convenience method that calls `read(b, 0, b.length)`.
`abstract 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`.
`int`	`readBit()` Reads a single bit from the stream and returns it as an `int` with the value `0` or `1`.
`long`	`readBits(int numBits)` Reads a bitstring from the stream and returns it as a `long`, with the first bit read becoming the most significant bit of the output.
`boolean`	`readBoolean()` Reads one input byte and returns `true` if that byte is nonzero, `false` if that byte is zero.
`byte`	`readByte()` Reads and returns one input byte.
`void`	`readBytes(IIOByteBuffer buf, int len)` Reads up to `len` bytes from the stream, and modifies the supplied `IIOByteBuffer` to indicate the byte array, offset, and length where the data may be found.
`char`	`readChar()` Reads an input `char` and returns the `char` value.
`double`	`readDouble()` Reads eight input bytes and returns a `double` value.
`float`	`readFloat()` Reads four input bytes and returns a `float` value.
`void`	`readFully(byte[] b)` Reads some bytes from an input stream and stores them into the buffer array `b`.
`void`	`readFully(byte[] b, int off, int len)` Reads `len` bytes from an input stream.
`void`	`readFully(char[] c, int off, int len)` Reads `len` chars (unsigned 16-bit integers) from the stream according to the current byte order, and stores them into `c` starting at index `off`.
`void`	`readFully(double[] d, int off, int len)` Reads `len` doubles (64-bit IEEE double-precision floats) from the stream according to the current byte order, and stores them into `d` starting at index `off`.
`void`	`readFully(float[] f, int off, int len)` Reads `len` floats (32-bit IEEE single-precision floats) from the stream according to the current byte order, and stores them into `f` starting at index `off`.
`void`	`readFully(int[] i, int off, int len)` Reads `len` ints (signed 32-bit integers) from the stream according to the current byte order, and stores them into `i` starting at index `off`.
`void`	`readFully(long[] l, int off, int len)` Reads `len` longs (signed 64-bit integers) from the stream according to the current byte order, and stores them into `l` starting at index `off`.
`void`	`readFully(short[] s, int off, int len)` Reads `len` shorts (signed 16-bit integers) from the stream according to the current byte order, and stores them into `s` starting at index `off`.
`int`	`readInt()` Reads four input bytes and returns an `int` value.
`String`	`readLine()` Reads the next line of text from the input stream.
`long`	`readLong()` Reads eight input bytes and returns a `long` value.
`short`	`readShort()` Reads two input bytes and returns a `short` value.
`int`	`readUnsignedByte()` Reads one input byte, zero-extends it to type `int`, and returns the result, which is therefore in the range `0` through `255`.
`long`	`readUnsignedInt()` Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order, converts the result to a long, masks it with `0xffffffffL` in order to strip off any sign-extension bits, and returns the result as an unsigned `long` value.
`int`	`readUnsignedShort()` Reads two input bytes and returns an `int` value in the range `0` through `65535`.
`String`	`readUTF()` Reads in a string that has been encoded using a modified UTF-8 format.
`void`	`reset()` Resets the current stream byte and bit positions from the stack of marked positions.
`void`	`seek(long pos)` Sets the current stream position to the desired location.
`void`	`setBitOffset(int bitOffset)` Sets the bit offset to an integer between 0 and 7, inclusive.
`void`	`setByteOrder(ByteOrder byteOrder)` Sets the desired byte order for future reads of data values from this stream.
`int`	`skipBytes(int n)` Advances the current stream position by calling `seek(getStreamPosition() + n)`.
`long`	`skipBytes(long n)` Advances the current stream position by calling `seek(getStreamPosition() + n)`.

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

Field Detail

byteOrder

protected ByteOrder byteOrder

The byte order of the stream as an instance of the enumeration class java.nio.ByteOrder, where ByteOrder.BIG_ENDIAN indicates network byte order and ByteOrder.LITTLE_ENDIAN indicates the reverse order. By default, the value is ByteOrder.BIG_ENDIAN.

streamPos

protected long streamPos

The current read position within the stream. Subclasses are responsible for keeping this value current from any method they override that alters the read position.

bitOffset

protected int bitOffset

The current bit offset within the stream. Subclasses are responsible for keeping this value current from any method they override that alters the bit offset.

flushedPos

protected long flushedPos

The position prior to which data may be discarded. Seeking to a smaller position is not allowed. flushedPos will always be >= 0.

Constructor Detail

ImageInputStreamImpl

public ImageInputStreamImpl()

Constructs an ImageInputStreamImpl.

Method Detail

checkClosed

protected final void checkClosed()
                          throws IOException

Throws an IOException if the stream has been closed. Subclasses may call this method from any of their methods that require the stream not to be closed.

Throws:: IOException - if the stream is closed.

setByteOrder

public void setByteOrder(ByteOrder byteOrder)

Description copied from interface: ImageInputStream

Sets the desired byte order for future reads of data values from this stream. For example, the sequence of bytes '0x01 0x02 0x03 0x04' if read as a 4-byte integer would have the value '0x01020304' using network byte order and the value '0x04030201' under the reverse byte order.

The enumeration class java.nio.ByteOrder is used to specify the byte order. A value of ByteOrder.BIG_ENDIAN specifies so-called big-endian or network byte order, in which the high-order byte comes first. Motorola and Sparc processors store data in this format, while Intel processors store data in the reverse ByteOrder.LITTLE_ENDIAN order.

The byte order has no effect on the results returned from the readBits method (or the value written by ImageOutputStream.writeBits).

Specified by:: setByteOrder in interface ImageInputStream

Parameters:: byteOrder - one of ByteOrder.BIG_ENDIAN or java.nio.ByteOrder.LITTLE_ENDIAN, indicating whether network byte order or its reverse will be used for future reads.
See Also:: ByteOrder, ImageInputStream.getByteOrder(), ImageInputStream.readBits(int)

getByteOrder

public ByteOrder getByteOrder()

Description copied from interface: ImageInputStream

Returns the byte order with which data values will be read from this stream as an instance of the java.nio.ByteOrder enumeration.

Specified by:: getByteOrder in interface ImageInputStream

Returns:: one of ByteOrder.BIG_ENDIAN or ByteOrder.LITTLE_ENDIAN, indicating which byte order is being used.
See Also:: ByteOrder, ImageInputStream.setByteOrder(java.nio.ByteOrder)

read

public abstract 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

Returns:: a byte value from the stream, as an int, or -1 to indicate EOF.
Throws:: IOException - if an I/O error occurs.

read

public int read(byte[] b)
         throws IOException

A convenience method that calls read(b, 0, b.length).

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

Specified by:: read in interface ImageInputStream

Parameters:: b - an array of bytes to be written to.
Returns:: the number of bytes actually read, or -1 to indicate EOF.
Throws:: NullPointerException - if b is null.; IOException - if an I/O error occurs.

read

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

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

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:: IndexOutOfBoundsException - if off is negative, len is negative, or off + len is greater than b.length.; NullPointerException - if b is null.; IOException - if an I/O error occurs.

readBytes

public void readBytes(IIOByteBuffer buf,
                      int len)
               throws IOException

Description copied from interface: ImageInputStream

Reads up to len bytes from the stream, and modifies the supplied IIOByteBuffer to indicate the byte array, offset, and length where the data may be found. The caller should not attempt to modify the data found in the IIOByteBuffer.

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

Specified by:: readBytes in interface ImageInputStream

Parameters:: buf - an IIOByteBuffer object to be modified.; len - the maximum number of bytes to read.
Throws:: IOException - if an I/O error occurs.

readBoolean

public boolean readBoolean()
                    throws IOException

Description copied from interface: DataInput

Reads one input byte and returns true if that byte is nonzero, false if that byte is zero. This method is suitable for reading the byte written by the writeBoolean method of interface DataOutput.

Specified by:: readBoolean in interface DataInput
Specified by:: readBoolean in interface ImageInputStream

Returns:: the boolean value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readByte

public byte readByte()
              throws IOException

Description copied from interface: DataInput

Reads and returns one input byte. The byte is treated as a signed value in the range -128 through 127, inclusive. This method is suitable for reading the byte written by the writeByte method of interface DataOutput.

Specified by:: readByte in interface DataInput
Specified by:: readByte in interface ImageInputStream

Returns:: the 8-bit value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readUnsignedByte

public int readUnsignedByte()
                     throws IOException

Description copied from interface: DataInput

Reads one input byte, zero-extends it to type int, and returns the result, which is therefore in the range 0 through 255. This method is suitable for reading the byte written by the writeByte method of interface DataOutput if the argument to writeByte was intended to be a value in the range 0 through 255.

Specified by:: readUnsignedByte in interface DataInput
Specified by:: readUnsignedByte in interface ImageInputStream

Returns:: the unsigned 8-bit value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readShort

public short readShort()
                throws IOException

Description copied from interface: DataInput

Reads two input bytes and returns a short value. Let a be the first byte read and b be the second byte. The value returned is:

(short)((a << 8) | (b & 0xff))

This method is suitable for reading the bytes written by the writeShort method of interface DataOutput.

Specified by:: readShort in interface DataInput
Specified by:: readShort in interface ImageInputStream

Returns:: the 16-bit value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.getByteOrder()

readUnsignedShort

public int readUnsignedShort()
                      throws IOException

Description copied from interface: DataInput

Reads two input bytes and returns an int value in the range 0 through 65535. Let a be the first byte read and b be the second byte. The value returned is:

(((a & 0xff) << 8) | (b & 0xff))

This method is suitable for reading the bytes written by the writeShort method of interface DataOutput if the argument to writeShort was intended to be a value in the range 0 through 65535.

Specified by:: readUnsignedShort in interface DataInput
Specified by:: readUnsignedShort in interface ImageInputStream

Returns:: the unsigned 16-bit value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.getByteOrder()

readChar

public char readChar()
              throws IOException

Description copied from interface: DataInput

Reads an input char and returns the char value. A Unicode char is made up of two bytes. Let a be the first byte read and b be the second byte. The value returned is:

(char)((a << 8) | (b & 0xff))

This method is suitable for reading bytes written by the writeChar method of interface DataOutput.

Specified by:: readChar in interface DataInput
Specified by:: readChar in interface ImageInputStream

Returns:: the Unicode char read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.readUnsignedShort()

readInt

public int readInt()
            throws IOException

Description copied from interface: DataInput

Reads four input bytes and returns an int value. Let a be the first byte read, b be the second byte, c be the third byte, and d be the fourth byte. The value returned is:

 
 (((a & 0xff) << 24) | ((b & 0xff) << 16) |
  ((c & 0xff) << 8) | (d & 0xff))

This method is suitable for reading bytes written by the writeInt method of interface DataOutput.

Specified by:: readInt in interface DataInput
Specified by:: readInt in interface ImageInputStream

Returns:: the int value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.getByteOrder()

readUnsignedInt

public long readUnsignedInt()
                     throws IOException

Description copied from interface: ImageInputStream

Reads 4 bytes from the stream, and (conceptually) concatenates them according to the current byte order, converts the result to a long, masks it with 0xffffffffL in order to strip off any sign-extension bits, and returns the result as an unsigned long value.

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

Specified by:: readUnsignedInt in interface ImageInputStream

Returns:: an unsigned int value from the stream, as a long.
Throws:: EOFException - if the stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.getByteOrder()

readLong

public long readLong()
              throws IOException

Description copied from interface: DataInput

Reads eight input bytes and returns a long value. Let a be the first byte read, b be the second byte, c be the third byte, d be the fourth byte, e be the fifth byte, f be the sixth byte, g be the seventh byte, and h be the eighth byte. The value returned is:

 
 (((long)(a & 0xff) << 56) |
  ((long)(b & 0xff) << 48) |
  ((long)(c & 0xff) << 40) |
  ((long)(d & 0xff) << 32) |
  ((long)(e & 0xff) << 24) |
  ((long)(f & 0xff) << 16) |
  ((long)(g & 0xff) <<  8) |
  ((long)(h & 0xff)))

This method is suitable for reading bytes written by the writeLong method of interface DataOutput.

Specified by:: readLong in interface DataInput
Specified by:: readLong in interface ImageInputStream

Returns:: the long value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.getByteOrder()

readFloat

public float readFloat()
                throws IOException

Description copied from interface: DataInput

Reads four input bytes and returns a float value. It does this by first constructing an int value in exactly the manner of the readInt method, then converting this int value to a float in exactly the manner of the method Float.intBitsToFloat. This method is suitable for reading bytes written by the writeFloat method of interface DataOutput.

Specified by:: readFloat in interface DataInput
Specified by:: readFloat in interface ImageInputStream

Returns:: the float value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.getByteOrder()

readDouble

public double readDouble()
                  throws IOException

Description copied from interface: DataInput

Reads eight input bytes and returns a double value. It does this by first constructing a long value in exactly the manner of the readlong method, then converting this long value to a double in exactly the manner of the method Double.longBitsToDouble. This method is suitable for reading bytes written by the writeDouble method of interface DataOutput.

Specified by:: readDouble in interface DataInput
Specified by:: readDouble in interface ImageInputStream

Returns:: the double value read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.
See Also:: ImageInputStream.getByteOrder()

readLine

public String readLine()
                throws IOException

Description copied from interface: DataInput

Reads the next line of text from the input stream. It reads successive bytes, converting each byte separately into a character, until it encounters a line terminator or end of file; the characters read are then returned as a String. Note that because this method processes bytes, it does not support input of the full Unicode character set.

If end of file is encountered before even one byte can be read, then null is returned. Otherwise, each byte that is read is converted to type char by zero-extension. If the character '\n' is encountered, it is discarded and reading ceases. If the character '\r' is encountered, it is discarded and, if the following byte converts to the character '\n', then that is discarded also; reading then ceases. If end of file is encountered before either of the characters '\n' and '\r' is encountered, reading ceases. Once reading has ceased, a String is returned that contains all the characters read and not discarded, taken in order. Note that every character in this string will have a value less than \u0100, that is, (char)256.

Specified by:: readLine in interface DataInput
Specified by:: readLine in interface ImageInputStream

Returns:: the next line of text from the input stream, or null if the end of file is encountered before a byte can be read.
Throws:: IOException - if an I/O error occurs.

readUTF

public String readUTF()
               throws IOException

Description copied from interface: DataInput

Reads in a string that has been encoded using a modified UTF-8 format. The general contract of readUTF is that it reads a representation of a Unicode character string encoded in modified UTF-8 format; this string of characters is then returned as a String.

First, two bytes are read and used to construct an unsigned 16-bit integer in exactly the manner of the readUnsignedShort method . This integer value is called the UTF length and specifies the number of additional bytes to be read. These bytes are then converted to characters by considering them in groups. The length of each group is computed from the value of the first byte of the group. The byte following a group, if any, is the first byte of the next group.

If the first byte of a group matches the bit pattern 0xxxxxxx (where x means "may be 0 or 1"), then the group consists of just that byte. The byte is zero-extended to form a character.

If the first byte of a group matches the bit pattern 110xxxxx, then the group consists of that byte a and a second byte b. If there is no byte b (because byte a was the last of the bytes to be read), or if byte b does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:

(char)(((a& 0x1F) << 6) | (b & 0x3F))

If the first byte of a group matches the bit pattern 1110xxxx, then the group consists of that byte a and two more bytes b and c. If there is no byte c (because byte a was one of the last two of the bytes to be read), or either byte b or byte c does not match the bit pattern 10xxxxxx, then a UTFDataFormatException is thrown. Otherwise, the group is converted to the character:


 (char)(((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F))

If the first byte of a group matches the pattern 1111xxxx or the pattern 10xxxxxx, then a UTFDataFormatException is thrown.

If end of file is encountered at any time during this entire process, then an EOFException is thrown.

After every group has been converted to a character by this process, the characters are gathered, in the same order in which their corresponding groups were read from the input stream, to form a String, which is returned.

The writeUTF method of interface DataOutput may be used to write data that is suitable for reading by this method.

Specified by:: readUTF in interface DataInput
Specified by:: readUTF in interface ImageInputStream

Returns:: a Unicode string.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.; UTFDataFormatException - if the bytes do not represent a valid modified UTF-8 encoding of a string.

readFully

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

Description copied from interface: DataInput

Reads len bytes from an input stream.

This method blocks until one of the following conditions occurs:

len bytes of input data are available, in which case a normal return is made.
End of file is detected, in which case an EOFException is thrown.
An I/O error occurs, in which case an IOException other than EOFException 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. Otherwise, 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.

Specified by:: readFully in interface DataInput
Specified by:: readFully in interface ImageInputStream

Parameters:: b - the buffer into which the data is read.; off - an int specifying the offset into the data.; len - an int specifying the number of bytes to read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readFully

public void readFully(byte[] b)
               throws IOException

Description copied from interface: DataInput

Reads some bytes from an input stream and stores them into the buffer array b. The number of bytes read is equal to the length of b.

This method blocks until one of the following conditions occurs:

b.length bytes of input data are available, in which case a normal return is made.
End of file is detected, in which case an EOFException is thrown.
An I/O error occurs, in which case an IOException other than EOFException is thrown.

If b is null, a NullPointerException is thrown. If b.length is zero, then no bytes are read. Otherwise, the first byte read is stored into element b[0], the next one into b[1], and so on. If an exception is thrown from this method, then it may be that some but not all bytes of b have been updated with data from the input stream.

Specified by:: readFully in interface DataInput
Specified by:: readFully in interface ImageInputStream

Parameters:: b - the buffer into which the data is read.
Throws:: EOFException - if this stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readFully

public void readFully(short[] s,
                      int off,
                      int len)
               throws IOException

Description copied from interface: ImageInputStream

Reads len shorts (signed 16-bit integers) from the stream according to the current byte order, and stores them into s starting at index off. If the end of the stream is reached, an EOFException will be thrown.

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

Specified by:: readFully in interface ImageInputStream

Parameters:: s - an array of shorts to be written to.; off - the starting position withinb to write to.; len - the maximum number of shorts to read.
Throws:: EOFException - if the stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readFully

public void readFully(char[] c,
                      int off,
                      int len)
               throws IOException

Description copied from interface: ImageInputStream

Reads len chars (unsigned 16-bit integers) from the stream according to the current byte order, and stores them into c starting at index off. If the end of the stream is reached, an EOFException will be thrown.

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

Specified by:: readFully in interface ImageInputStream

Parameters:: c - an array of chars to be written to.; off - the starting position withinb to write to.; len - the maximum number of chars to read.
Throws:: EOFException - if the stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readFully

public void readFully(int[] i,
                      int off,
                      int len)
               throws IOException

Description copied from interface: ImageInputStream

Reads len ints (signed 32-bit integers) from the stream according to the current byte order, and stores them into i starting at index off. If the end of the stream is reached, an EOFException will be thrown.

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

Specified by:: readFully in interface ImageInputStream

Parameters:: i - an array of ints to be written to.; off - the starting position withinb to write to.; len - the maximum number of ints to read.
Throws:: EOFException - if the stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readFully

public void readFully(long[] l,
                      int off,
                      int len)
               throws IOException

Description copied from interface: ImageInputStream

Reads len longs (signed 64-bit integers) from the stream according to the current byte order, and stores them into l starting at index off. If the end of the stream is reached, an EOFException will be thrown.

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

Specified by:: readFully in interface ImageInputStream

Parameters:: l - an array of longs to be written to.; off - the starting position withinb to write to.; len - the maximum number of longs to read.
Throws:: EOFException - if the stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readFully

public void readFully(float[] f,
                      int off,
                      int len)
               throws IOException

Description copied from interface: ImageInputStream

Reads len floats (32-bit IEEE single-precision floats) from the stream according to the current byte order, and stores them into f starting at index off. If the end of the stream is reached, an EOFException will be thrown.

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

Specified by:: readFully in interface ImageInputStream

Parameters:: f - an array of floats to be written to.; off - the starting position withinb to write to.; len - the maximum number of floats to read.
Throws:: EOFException - if the stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

readFully

public void readFully(double[] d,
                      int off,
                      int len)
               throws IOException

Description copied from interface: ImageInputStream

Reads len doubles (64-bit IEEE double-precision floats) from the stream according to the current byte order, and stores them into d starting at index off. If the end of the stream is reached, an EOFException will be thrown.

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

Specified by:: readFully in interface ImageInputStream

Parameters:: d - an array of doubles to be written to.; off - the starting position withinb to write to.; len - the maximum number of doubles to read.
Throws:: EOFException - if the stream reaches the end before reading all the bytes.; IOException - if an I/O error occurs.

getStreamPosition

public long getStreamPosition()
                       throws IOException

Description copied from interface: ImageInputStream

Returns the current byte position of the stream. The next read will take place starting at this offset.

Specified by:: getStreamPosition in interface ImageInputStream

Returns:: a long containing the position of the stream.
Throws:: IOException - if an I/O error occurs.

getBitOffset

public int getBitOffset()
                 throws IOException

Description copied from interface: ImageInputStream

Returns the current bit offset, as an integer between 0 and 7, inclusive. The bit offset is updated implicitly by calls to the readBits method. A value of 0 indicates the most-significant bit, and a value of 7 indicates the least significant bit, of the byte being read.

The bit offset is set to 0 when a stream is first opened, and is reset to 0 by calls to seek, skipBytes, or any read or readFully method.

Specified by:: getBitOffset in interface ImageInputStream

Returns:: an int containing the bit offset between 0 and 7, inclusive.
Throws:: IOException - if an I/O error occurs.
See Also:: ImageInputStream.setBitOffset(int)

setBitOffset

public void setBitOffset(int bitOffset)
                  throws IOException

Description copied from interface: ImageInputStream

Sets the bit offset to an integer between 0 and 7, inclusive. The byte offset within the stream, as returned by getStreamPosition, is left unchanged. A value of 0 indicates the most-significant bit, and a value of 7 indicates the least significant bit, of the byte being read.

Specified by:: setBitOffset in interface ImageInputStream

Parameters:: bitOffset - the desired offset, as an int between 0 and 7, inclusive.
Throws:: IOException - if an I/O error occurs.
See Also:: ImageInputStream.getBitOffset()

readBit

public int readBit()
            throws IOException

Description copied from interface: ImageInputStream

Reads a single bit from the stream and returns it as an int with the value 0 or 1. The bit offset is advanced by one and reduced modulo 8.

Specified by:: readBit in interface ImageInputStream

Returns:: an int containing the value 0 or 1.
Throws:: EOFException - if the stream reaches the end before reading all the bits.; IOException - if an I/O error occurs.

readBits

public long readBits(int numBits)
              throws IOException

Description copied from interface: ImageInputStream

Reads a bitstring from the stream and returns it as a long, with the first bit read becoming the most significant bit of the output. The read starts within the byte indicated by getStreamPosition, at the bit given by getBitOffset. The bit offset is advanced by numBits and reduced modulo 8.

The byte order of the stream has no effect on this method. The return value of this method is constructed as though the bits were read one at a time, and shifted into the right side of the return value, as shown by the following pseudo-code:

 long accum = 0L;
 for (int i = 0; i < numBits; i++) {
   accum <<= 1; // Shift left one bit to make room
   accum |= readBit();
 }

Note that the result of readBits(32) may thus not be equal to that of readInt() if a reverse network byte order is being used (i.e.,

getByteOrder() ==
 false

If the end of the stream is encountered before all the bits have been read, an EOFException is thrown.

Specified by:: readBits in interface ImageInputStream

Parameters:: numBits - the number of bits to read, as an int between 0 and 64, inclusive.
Returns:: the bitstring, as a long with the last bit read stored in the least significant bit.
Throws:: EOFException - if the stream reaches the end before reading all the bits.; IOException - if an I/O error occurs.

length

public long length()

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

Returns:: -1L to indicate unknown length.

skipBytes

public int skipBytes(int n)
              throws IOException

Advances the current stream position by calling seek(getStreamPosition() + n).

The bit offset is reset to zero.

Specified by:: skipBytes in interface DataInput
Specified by:: skipBytes in interface ImageInputStream

Parameters:: n - the number of bytes to seek forward.
Returns:: an int representing the number of bytes skipped.
Throws:: IOException - if getStreamPosition throws an IOException when computing either the starting or ending position.

skipBytes

public long skipBytes(long n)
               throws IOException

Advances the current stream position by calling seek(getStreamPosition() + n).

The bit offset is reset to zero.

Specified by:: skipBytes in interface ImageInputStream

Parameters:: n - the number of bytes to seek forward.
Returns:: a long representing the number of bytes skipped.
Throws:: IOException - if getStreamPosition throws an IOException when computing either the starting or ending position.

seek

public void seek(long pos)
          throws IOException

Description copied from interface: ImageInputStream

Sets the current stream position to the desired location. The next read will occur at this location. The bit offset is set to 0.

An IndexOutOfBoundsException will be thrown if pos is smaller than the flushed position (as returned by getflushedPosition).

It is legal to seek past the end of the file; an EOFException will be thrown only if a read is performed.

Specified by:: seek in interface ImageInputStream

Parameters:: pos - a long containing the desired file pointer position.
Throws:: IOException - if any other I/O error occurs.

mark

public void mark()

Pushes the current stream position onto a stack of marked positions.

Specified by:: mark in interface ImageInputStream

reset

public void reset()
           throws IOException

Resets the current stream byte and bit positions from the stack of marked positions.

An IOException will be thrown if the previous marked position lies in the discarded portion of the stream.

Specified by:: reset in interface ImageInputStream

Throws:: IOException - if an I/O error occurs.

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

Parameters:: pos - a long containing the length of the file prefix that may be flushed.
Throws:: IOException - if an I/O error occurs.

flush

public void flush()
           throws IOException

Description copied from interface: ImageInputStream

Discards the initial position of the stream prior to the current stream position. Equivalent to flushBefore(getStreamPosition()).

Specified by:: flush in interface ImageInputStream

Throws:: IOException - if an I/O error occurs.

getFlushedPosition

public long getFlushedPosition()

Description copied from interface: ImageInputStream

Returns the earliest position in the stream to which seeking may be performed. The returned value will be the maximum of all values passed into previous calls to flushBefore.

Specified by:: getFlushedPosition in interface ImageInputStream

Returns:: the earliest legal position for seeking, as a long.

isCached

public boolean isCached()

Default implementation returns false. Subclasses should override this if they cache data.

Specified by:: isCached in interface ImageInputStream

Returns:: true if this ImageInputStream caches data.
See Also:: ImageInputStream.isCachedMemory(), ImageInputStream.isCachedFile()

isCachedMemory

public boolean isCachedMemory()

Default implementation returns false. Subclasses should override this if they cache data in main memory.

Specified by:: isCachedMemory in interface ImageInputStream

Returns:: true if this ImageInputStream caches data in main memory.
See Also:: ImageInputStream.isCached(), ImageInputStream.isCachedFile()

isCachedFile

public boolean isCachedFile()

Default implementation returns false. Subclasses should override this if they cache data in a temporary file.

Specified by:: isCachedFile in interface ImageInputStream

Returns:: true if this ImageInputStream caches data in a temporary file.
See Also:: ImageInputStream.isCached(), ImageInputStream.isCachedMemory()

close

public void close()
           throws IOException

Description copied from interface: ImageInputStream

Closes the stream. Attempts to access a stream that has been closed may result in IOExceptions or incorrect behavior. Calling this method may allow classes implementing this interface to release resources associated with the stream such as memory, disk space, or file descriptors.

Specified by:: close in interface ImageInputStream

Throws:: IOException - if an I/O error occurs.

finalize

protected void finalize()
                 throws Throwable

Finalizes this object prior to garbage collection. The close method is called to close any open input source. This method should not be called from application code.

Overrides:: finalize in class Object

Throws:: Throwable - if an error occurs during superclass finalization.

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

javax.imageio.stream Class ImageInputStreamImpl

byteOrder

streamPos

bitOffset

flushedPos

ImageInputStreamImpl

checkClosed

setByteOrder

getByteOrder

read

read

read

readBytes

readBoolean

readByte

readUnsignedByte

readShort

readUnsignedShort

readChar

readInt

readUnsignedInt

readLong

readFloat

readDouble

readLine

readUTF

readFully

readFully

readFully

readFully

readFully

readFully

readFully

readFully

getStreamPosition

getBitOffset

setBitOffset

readBit

readBits

length

skipBytes

skipBytes

seek

mark

reset

flushBefore

flush

getFlushedPosition

isCached

isCachedMemory

isCachedFile

close

finalize

javax.imageio.stream
Class ImageInputStreamImpl