org.apache.batik.ext.awt.image.codec.util
Class SeekableStream

java.lang.Object
  extended by java.io.InputStream
      extended by org.apache.batik.ext.awt.image.codec.util.SeekableStream
All Implemented Interfaces:
Closeable, DataInput
Direct Known Subclasses:
FileCacheSeekableStream, ForwardSeekableStream, MemoryCacheSeekableStream

public abstract class SeekableStream
extends InputStream
implements DataInput

An abstract subclass of java.io.InputStream that allows seeking within the input, similar to the RandomAccessFile class. Additionally, the DataInput interface is supported and extended to include support for little-endian representations of fundamental data types.

In addition to the familiar methods from InputStream, the methods getFilePointer(), seek(), are defined as in the RandomAccessFile class. The canSeekBackwards() method will return true if it is permissible to seek to a position earlier in the stream than the current value of getFilePointer(). Some subclasses of SeekableStream guarantee the ability to seek backwards while others may not offer this feature in the interest of providing greater efficiency for those users who do not require it.

The DataInput interface is supported as well. This included the skipBytes() and readFully() methods and a variety of read methods for various data types.

A number of concrete subclasses of SeekableStream are supplied in the com.sun.media.jai.codec package.

Three classes are provided for the purpose of adapting a standard InputStream to the SeekableStream interface. ForwardSeekableStream does not allows seeking backwards, but is inexpensive to use. FileCacheSeekableStream maintains a copy of all of the data read from the input in a temporary file; this file will be discarded automatically when the FileSeekableStream is finalized, or when the JVM exits normally. FileCacheSeekableStream is intended to be reasonably efficient apart from the unavoidable use of disk space. In circumstances where the creation of a temporary file is not possible, MemoryCacheSeekableStream may be used. MemoryCacheSeekableStream creates a potentially large in-memory buffer to store the stream data and so should be avoided when possible.

The FileSeekableStream class wraps a File or RandomAccessFile. It forwards requests to the real underlying file. It performs a limited amount of caching in order to avoid excessive I/O costs.

The SegmentedSeekableStream class performs a different sort of function. It creates a SeekableStream from another SeekableStream by selecting a series of portions or "segments". Each segment starts at a specified location within the source SeekableStream and extends for a specified number of bytes. The StreamSegmentMapper interface and StreamSegment class may be used to compute the segment positions dynamically.

A convenience methods, wrapInputStream is provided to construct a suitable SeekableStream instance whose data is supplied by a given InputStream. The caller, by means of the canSeekBackwards parameter, determines whether support for seeking backwards is required.


Field Summary
protected  long markPos
          Marked position, shared by ForwardSeekableStream
 
Constructor Summary
SeekableStream()
           
 
Method Summary
 boolean canSeekBackwards()
          Returns true if this object supports calls to seek(pos) with an offset pos smaller than the current offset, as returned by getFilePointer.
protected  void finalize()
          Releases any system resources associated with this stream by calling the close() method.
abstract  long getFilePointer()
          Returns the current offset in this stream.
 void mark(int readLimit)
          Marks the current file position for later return using the reset() method.
 boolean markSupported()
          Returns true if marking is supported.
abstract  int read()
          Reads the next byte of data from the input stream.
abstract  int read(byte[] b, int off, int len)
          Reads up to len bytes of data from the input stream into an array of bytes.
 boolean readBoolean()
          Reads a boolean from this stream.
 byte readByte()
          Reads a signed eight-bit value from this stream.
 char readChar()
          Reads a Unicode character from this stream.
 char readCharLE()
          Reads a Unicode character from this stream in little-endian order.
 double readDouble()
          Reads a double from this stream.
 double readDoubleLE()
          Reads a double from this stream in little-endian order.
 float readFloat()
          Reads a float from this stream.
 float readFloatLE()
          Reads a float from this stream in little-endian order.
 void readFully(byte[] b)
          Reads b.length bytes from this stream into the byte array, starting at the current stream pointer.
 void readFully(byte[] b, int off, int len)
          Reads exactly len bytes from this stream into the byte array, starting at the current stream pointer.
 int readInt()
          Reads a signed 32-bit integer from this stream.
 int readIntLE()
          Reads a signed 32-bit integer from this stream in little-endian order.
 String readLine()
          Reads the next line of text from this stream.
 long readLong()
          Reads a signed 64-bit integer from this stream.
 long readLongLE()
          Reads a signed 64-bit integer from this stream in little-endian order.
 short readShort()
          Reads a signed 16-bit number from this stream.
 short readShortLE()
          Reads a signed 16-bit number from this stream in little-endian order.
 int readUnsignedByte()
          Reads an unsigned eight-bit number from this stream.
 long readUnsignedInt()
          Reads an unsigned 32-bit integer from this stream.
 long readUnsignedIntLE()
          Reads an unsigned 32-bit integer from this stream in little-endian order.
 int readUnsignedShort()
          Reads an unsigned 16-bit number from this stream.
 int readUnsignedShortLE()
          Reads an unsigned 16-bit number from this stream in little-endian order.
 String readUTF()
          Reads in a string from this stream.
 void reset()
          Returns the file position to its position at the time of the immediately previous call to the mark() method.
abstract  void seek(long pos)
          Sets the offset, measured from the beginning of this stream, at which the next read occurs.
 int skipBytes(int n)
          Attempts to skip over n bytes of input discarding the skipped bytes.
static SeekableStream wrapInputStream(InputStream is, boolean canSeekBackwards)
          Returns a SeekableStream that will read from a given InputStream, optionally including support for seeking backwards.
 
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

markPos

protected long markPos
Marked position, shared by ForwardSeekableStream

Constructor Detail

SeekableStream

public SeekableStream()
Method Detail

wrapInputStream

public static SeekableStream wrapInputStream(InputStream is,
                                             boolean canSeekBackwards)
Returns a SeekableStream that will read from a given InputStream, optionally including support for seeking backwards. This is a convenience method that avoids the need to instantiate specific subclasses of SeekableStream depending on the current security model.

Parameters:
is - An InputStream.
canSeekBackwards - true if the ability to seek backwards in the output is required.
Returns:
An instance of SeekableStream.

read

public abstract 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.

A subclass must provide an implementation of this method.

Specified by:
read in class InputStream
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 abstract 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 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.

A subclass must provide an implementation of this method.

Overrides:
read in class InputStream
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.

mark

public void mark(int readLimit)
Marks the current file position for later return using the reset() method.

Overrides:
mark in class InputStream

reset

public void reset()
           throws IOException
Returns the file position to its position at the time of the immediately previous call to the mark() method.

Overrides:
reset in class InputStream
Throws:
IOException

markSupported

public boolean markSupported()
Returns true if marking is supported. Marking is automatically supported for SeekableStream subclasses that support seeking backeards. Subclasses that do not support seeking backwards but do support marking must override this method.

Overrides:
markSupported in class InputStream

canSeekBackwards

public boolean canSeekBackwards()
Returns true if this object supports calls to seek(pos) with an offset pos smaller than the current offset, as returned by getFilePointer.


getFilePointer

public abstract long getFilePointer()
                             throws IOException
Returns the current offset in this stream.

Returns:
the offset from the beginning of the stream, in bytes, at which the next read occurs.
Throws:
IOException - if an I/O error occurs.

seek

public abstract void seek(long pos)
                   throws 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.

Parameters:
pos - the offset position, measured in bytes from the beginning of the stream, at which to set the stream pointer.
Throws:
IOException - if pos is less than 0 or if an I/O error occurs.

readFully

public final void readFully(byte[] b)
                     throws IOException
Reads b.length bytes from this stream into the byte array, starting at the current stream pointer. This method reads repeatedly from the stream until the requested number of bytes are read. This method blocks until the requested number of bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readFully in interface DataInput
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 final void readFully(byte[] b,
                            int off,
                            int len)
                     throws IOException
Reads exactly len bytes from this stream into the byte array, starting at the current stream pointer. This method reads repeatedly from the stream until the requested number of bytes are read. This method blocks until the requested number of bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readFully in interface DataInput
Parameters:
b - the buffer into which the data is read.
off - the start offset of the data.
len - 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.

skipBytes

public int skipBytes(int n)
              throws IOException
Attempts to skip over n bytes of input discarding the skipped bytes.

This method may skip over some smaller number of bytes, possibly zero. This may result from any of a number of conditions; reaching end of stream before n bytes have been skipped is only one possibility. This method never throws an EOFException. The actual number of bytes skipped is returned. If n is negative, no bytes are skipped.

Specified by:
skipBytes in interface DataInput
Parameters:
n - the number of bytes to be skipped.
Returns:
the actual number of bytes skipped.
Throws:
IOException - if an I/O error occurs.

readBoolean

public final boolean readBoolean()
                          throws IOException
Reads a boolean from this stream. This method reads a single byte from the stream, starting at the current stream pointer. A value of 0 represents false. Any other value represents true. This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.

Specified by:
readBoolean in interface DataInput
Returns:
the boolean value read.
Throws:
EOFException - if this stream has reached the end.
IOException - if an I/O error occurs.

readByte

public final byte readByte()
                    throws IOException
Reads a signed eight-bit value from this stream. This method reads a byte from the stream, starting from the current stream pointer. If the byte read is b, where 0 <= b <= 255, then the result is:
     (byte)(b)
 

This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.

Specified by:
readByte in interface DataInput
Returns:
the next byte of this stream as a signed eight-bit byte.
Throws:
EOFException - if this stream has reached the end.
IOException - if an I/O error occurs.

readUnsignedByte

public final int readUnsignedByte()
                           throws IOException
Reads an unsigned eight-bit number from this stream. This method reads a byte from this stream, starting at the current stream pointer, and returns that byte.

This method blocks until the byte is read, the end of the stream is detected, or an exception is thrown.

Specified by:
readUnsignedByte in interface DataInput
Returns:
the next byte of this stream, interpreted as an unsigned eight-bit number.
Throws:
EOFException - if this stream has reached the end.
IOException - if an I/O error occurs.

readShort

public final short readShort()
                      throws IOException
Reads a signed 16-bit number from this stream. The method reads two bytes from this stream, starting at the current stream pointer. If the two bytes read, in order, are b1 and b2, where each of the two values is between 0 and 255, inclusive, then the result is equal to:
     (short)((b1 << 8) | b2)
 

This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readShort in interface DataInput
Returns:
the next two bytes of this stream, interpreted as a signed 16-bit number.
Throws:
EOFException - if this stream reaches the end before reading two bytes.
IOException - if an I/O error occurs.

readShortLE

public final short readShortLE()
                        throws IOException
Reads a signed 16-bit number from this stream in little-endian order. The method reads two bytes from this stream, starting at the current stream pointer. If the two bytes read, in order, are b1 and b2, where each of the two values is between 0 and 255, inclusive, then the result is equal to:
     (short)((b2 << 8) | b1)
 

This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next two bytes of this stream, interpreted as a signed 16-bit number.
Throws:
EOFException - if this stream reaches the end before reading two bytes.
IOException - if an I/O error occurs.

readUnsignedShort

public final int readUnsignedShort()
                            throws IOException
Reads an unsigned 16-bit number from this stream. This method reads two bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1 and b2, where 0 <= b1, b2 <= 255, then the result is equal to:
     (b1 << 8) | b2
 

This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readUnsignedShort in interface DataInput
Returns:
the next two bytes of this stream, interpreted as an unsigned 16-bit integer.
Throws:
EOFException - if this stream reaches the end before reading two bytes.
IOException - if an I/O error occurs.

readUnsignedShortLE

public final int readUnsignedShortLE()
                              throws IOException
Reads an unsigned 16-bit number from this stream in little-endian order. This method reads two bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1 and b2, where 0 <= b1, b2 <= 255, then the result is equal to:
     (b2 << 8) | b1
 

This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next two bytes of this stream, interpreted as an unsigned 16-bit integer.
Throws:
EOFException - if this stream reaches the end before reading two bytes.
IOException - if an I/O error occurs.

readChar

public final char readChar()
                    throws IOException
Reads a Unicode character from this stream. This method reads two bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1 and b2, where 0 <= b1, b2 <= 255, then the result is equal to:
     (char)((b1 << 8) | b2)
 

This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readChar in interface DataInput
Returns:
the next two bytes of this stream as a Unicode character.
Throws:
EOFException - if this stream reaches the end before reading two bytes.
IOException - if an I/O error occurs.

readCharLE

public final char readCharLE()
                      throws IOException
Reads a Unicode character from this stream in little-endian order. This method reads two bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1 and b2, where 0 <= b1, b2 <= 255, then the result is equal to:
     (char)((b2 << 8) | b1)
 

This method blocks until the two bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next two bytes of this stream as a Unicode character.
Throws:
EOFException - if this stream reaches the end before reading two bytes.
IOException - if an I/O error occurs.

readInt

public final int readInt()
                  throws IOException
Reads a signed 32-bit integer from this stream. This method reads 4 bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1, b2, b3, and b4, where 0 <= b1, b2, b3, b4 <= 255, then the result is equal to:
     (b1 << 24) | (b2 << 16) + (b3 << 8) + b4
 

This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readInt in interface DataInput
Returns:
the next four bytes of this stream, interpreted as an int.
Throws:
EOFException - if this stream reaches the end before reading four bytes.
IOException - if an I/O error occurs.

readIntLE

public final int readIntLE()
                    throws IOException
Reads a signed 32-bit integer from this stream in little-endian order. This method reads 4 bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1, b2, b3, and b4, where 0 <= b1, b2, b3, b4 <= 255, then the result is equal to:
     (b4 << 24) | (b3 << 16) + (b2 << 8) + b1
 

This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next four bytes of this stream, interpreted as an int.
Throws:
EOFException - if this stream reaches the end before reading four bytes.
IOException - if an I/O error occurs.

readUnsignedInt

public final long readUnsignedInt()
                           throws IOException
Reads an unsigned 32-bit integer from this stream. This method reads 4 bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1, b2, b3, and b4, where 0 <= b1, b2, b3, b4 <= 255, then the result is equal to:
     (b1 << 24) | (b2 << 16) + (b3 << 8) + b4
 

This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next four bytes of this stream, interpreted as a long.
Throws:
EOFException - if this stream reaches the end before reading four bytes.
IOException - if an I/O error occurs.

readUnsignedIntLE

public final long readUnsignedIntLE()
                             throws IOException
Reads an unsigned 32-bit integer from this stream in little-endian order. This method reads 4 bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1, b2, b3, and b4, where 0 <= b1, b2, b3, b4 <= 255, then the result is equal to:
     (b4 << 24) | (b3 << 16) + (b2 << 8) + b1
 

This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next four bytes of this stream, interpreted as a long.
Throws:
EOFException - if this stream reaches the end before reading four bytes.
IOException - if an I/O error occurs.

readLong

public final long readLong()
                    throws IOException
Reads a signed 64-bit integer from this stream. This method reads eight bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1, b2, b3, b4, b5, b6, b7, and b8, where:
     0 <= b1, b2, b3, b4, b5, b6, b7, b8 <=255,
 

then the result is equal to:

     ((long)b1 << 56) + ((long)b2 << 48)
     + ((long)b3 << 40) + ((long)b4 << 32)
     + ((long)b5 << 24) + ((long)b6 << 16)
     + ((long)b7 << 8) + b8
 

This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readLong in interface DataInput
Returns:
the next eight bytes of this stream, interpreted as a long.
Throws:
EOFException - if this stream reaches the end before reading eight bytes.
IOException - if an I/O error occurs.

readLongLE

public final long readLongLE()
                      throws IOException
Reads a signed 64-bit integer from this stream in little-endian order. This method reads eight bytes from the stream, starting at the current stream pointer. If the bytes read, in order, are b1, b2, b3, b4, b5, b6, b7, and b8, where:
     0 <= b1, b2, b3, b4, b5, b6, b7, b8 <=255,
 

then the result is equal to:

     ((long)b1 << 56) + ((long)b2 << 48)
     + ((long)b3 << 40) + ((long)b4 << 32)
     + ((long)b5 << 24) + ((long)b6 << 16)
     + ((long)b7 << 8) + b8
 

This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next eight bytes of this stream, interpreted as a long.
Throws:
EOFException - if this stream reaches the end before reading eight bytes.
IOException - if an I/O error occurs.

readFloat

public final float readFloat()
                      throws IOException
Reads a float from this stream. This method reads an int value, starting at the current stream pointer, as if by the readInt method and then converts that int to a float using the intBitsToFloat method in class Float.

This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readFloat in interface DataInput
Returns:
the next four bytes of this stream, interpreted as a float.
Throws:
EOFException - if this stream reaches the end before reading four bytes.
IOException - if an I/O error occurs.

readFloatLE

public final float readFloatLE()
                        throws IOException
Reads a float from this stream in little-endian order. This method reads an int value, starting at the current stream pointer, as if by the readInt method and then converts that int to a float using the intBitsToFloat method in class Float.

This method blocks until the four bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next four bytes of this stream, interpreted as a float.
Throws:
EOFException - if this stream reaches the end before reading four bytes.
IOException - if an I/O error occurs.

readDouble

public final double readDouble()
                        throws IOException
Reads a double from this stream. This method reads a long value, starting at the current stream pointer, as if by the readLong method and then converts that long to a double using the longBitsToDouble method in class Double.

This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readDouble in interface DataInput
Returns:
the next eight bytes of this stream, interpreted as a double.
Throws:
EOFException - if this stream reaches the end before reading eight bytes.
IOException - if an I/O error occurs.

readDoubleLE

public final double readDoubleLE()
                          throws IOException
Reads a double from this stream in little-endian order. This method reads a long value, starting at the current stream pointer, as if by the readLong method and then converts that long to a double using the longBitsToDouble method in class Double.

This method blocks until the eight bytes are read, the end of the stream is detected, or an exception is thrown.

Returns:
the next eight bytes of this stream, interpreted as a double.
Throws:
EOFException - if this stream reaches the end before reading eight bytes.
IOException - if an I/O error occurs.

readLine

public final String readLine()
                      throws IOException
Reads the next line of text from this stream. This method successively reads bytes from the stream, starting at the current stream pointer, until it reaches a line terminator or the end of the stream. Each byte is converted into a character by taking the byte's value for the lower eight bits of the character and setting the high eight bits of the character to zero. This method does not, therefore, support the full Unicode character set.

A line of text is terminated by a carriage-return character ('\r'), a newline character ('\n'), a carriage-return character immediately followed by a newline character, or the end of the stream. Line-terminating characters are discarded and are not included as part of the string returned.

This method blocks until a newline character is read, a carriage return and the byte following it are read (to see if it is a newline), the end of the stream is reached, or an exception is thrown.

Specified by:
readLine in interface DataInput
Returns:
the next line of text from this stream, or null if end of stream is encountered before even one byte is read.
Throws:
IOException - if an I/O error occurs.

readUTF

public final String readUTF()
                     throws IOException
Reads in a string from this stream. The string has been encoded using a modified UTF-8 format.

The first two bytes are read, starting from the current stream pointer, as if by readUnsignedShort. This value gives the number of following bytes that are in the encoded string, not the length of the resulting string. The following bytes are then interpreted as bytes encoding characters in the UTF-8 format and are converted into characters.

This method blocks until all the bytes are read, the end of the stream is detected, or an exception is thrown.

Specified by:
readUTF in interface DataInput
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 valid UTF-8 encoding of a Unicode string.

finalize

protected void finalize()
                 throws Throwable
Releases any system resources associated with this stream by calling the close() method.

Overrides:
finalize in class Object
Throws:
Throwable


Copyright © 2008 Apache Software Foundation. All Rights Reserved.