public abstract class

CharacterDecoder

extends Object
java.lang.Object
   ↳ sun.misc.CharacterDecoder
Known Direct Subclasses

Class Overview

This class defines the decoding half of character encoders. A character decoder is an algorithim for transforming 8 bit binary data that has been encoded into text by a character encoder, back into original binary form. The character encoders, in general, have been structured around a central theme that binary data can be encoded into text that has the form: 

      [Buffer Prefix]
      [Line Prefix][encoded data atoms][Line Suffix]
      [Buffer Suffix]
Of course in the simplest encoding schemes, the buffer has no distinct prefix of suffix, however all have some fixed relationship between the text in an 'atom' and the binary data itself. In the CharacterEncoder and CharacterDecoder classes, one complete chunk of data is referred to as a buffer. Encoded buffers are all text, and decoded buffers (sometimes just referred to as buffers) are binary octets. To create a custom decoder, you must, at a minimum, overide three abstract methods in this class.
bytesPerAtom which tells the decoder how many bytes to expect from decodeAtom
decodeAtom which decodes the bytes sent to it as text.
bytesPerLine which tells the encoder the maximum number of bytes per line.
In general, the character decoders return error in the form of a CEFormatException. The syntax of the detail string is 
      DecoderClassName: Error message.
Several useful decoders have already been written and are referenced in the See Also list below.

See Also

Summary

Public Constructors
CharacterDecoder()
Public Methods
void decodeBuffer(InputStream aStream, OutputStream bStream)
Decode the text from the InputStream and write the decoded octets to the OutputStream.
byte[] decodeBuffer(InputStream in)
Decode the contents of the inputstream into a buffer.
byte[] decodeBuffer(String inputString)
Alternate decode interface that takes a String containing the encoded buffer and returns a byte array containing the data.
ByteBuffer decodeBufferToByteBuffer(InputStream in)
Decode the contents of the inputStream into a ByteBuffer.
ByteBuffer decodeBufferToByteBuffer(String inputString)
Decode the contents of the String into a ByteBuffer.
Protected Methods
abstract int bytesPerAtom()
Return the number of bytes per atom of decoding
abstract int bytesPerLine()
Return the maximum number of bytes that can be encoded per line
void decodeAtom(PushbackInputStream aStream, OutputStream bStream, int l)
This method does an actual decode.
void decodeBufferPrefix(PushbackInputStream aStream, OutputStream bStream)
decode the beginning of the buffer, by default this is a NOP.
void decodeBufferSuffix(PushbackInputStream aStream, OutputStream bStream)
decode the buffer suffix, again by default it is a NOP.
int decodeLinePrefix(PushbackInputStream aStream, OutputStream bStream)
This method should return, if it knows, the number of bytes that will be decoded.
void decodeLineSuffix(PushbackInputStream aStream, OutputStream bStream)
This method post processes the line, if there are error detection or correction codes in a line, they are generally processed by this method.
int readFully(InputStream in, byte[] buffer, int offset, int len)
This method works around the bizarre semantics of BufferedInputStream's read method.
[Expand]
Inherited Methods
From class java.lang.Object

Public Constructors

public CharacterDecoder ()

Public Methods

public void decodeBuffer (InputStream aStream, OutputStream bStream)

Decode the text from the InputStream and write the decoded octets to the OutputStream. This method runs until the stream is exhausted.

Throws
CEFormatException An error has occured while decoding
CEStreamExhausted The input stream is unexpectedly out of data
IOException

public byte[] decodeBuffer (InputStream in)

Decode the contents of the inputstream into a buffer.

Throws
IOException

public byte[] decodeBuffer (String inputString)

Alternate decode interface that takes a String containing the encoded buffer and returns a byte array containing the data.

Throws
CEFormatException An error has occured while decoding
IOException

public ByteBuffer decodeBufferToByteBuffer (InputStream in)

Decode the contents of the inputStream into a ByteBuffer.

Throws
IOException

public ByteBuffer decodeBufferToByteBuffer (String inputString)

Decode the contents of the String into a ByteBuffer.

Throws
IOException

Protected Methods

protected abstract int bytesPerAtom ()

Return the number of bytes per atom of decoding

protected abstract int bytesPerLine ()

Return the maximum number of bytes that can be encoded per line

protected void decodeAtom (PushbackInputStream aStream, OutputStream bStream, int l)

This method does an actual decode. It takes the decoded bytes and writes them to the OutputStream. The integer l tells the method how many bytes are required. This is always <= bytesPerAtom().

Throws
IOException

protected void decodeBufferPrefix (PushbackInputStream aStream, OutputStream bStream)

decode the beginning of the buffer, by default this is a NOP.

Throws
IOException

protected void decodeBufferSuffix (PushbackInputStream aStream, OutputStream bStream)

decode the buffer suffix, again by default it is a NOP.

Throws
IOException

protected int decodeLinePrefix (PushbackInputStream aStream, OutputStream bStream)

This method should return, if it knows, the number of bytes that will be decoded. Many formats such as uuencoding provide this information. By default we return the maximum bytes that could have been encoded on the line.

Throws
IOException

protected void decodeLineSuffix (PushbackInputStream aStream, OutputStream bStream)

This method post processes the line, if there are error detection or correction codes in a line, they are generally processed by this method. The simplest version of this method looks for the (newline) character.

Throws
IOException

protected int readFully (InputStream in, byte[] buffer, int offset, int len)

This method works around the bizarre semantics of BufferedInputStream's read method.

Throws
IOException