sun.misc

Class CharacterDecoder

java.lang.Object

sun.misc.CharacterDecoder

Direct Known Subclasses:

BASE64Decoder

public abstract class CharacterDecoder
extends java.lang.Object

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.

Author:

Chuck McManis

See Also:

CEFormatException, CharacterEncoder, UCDecoder, UUDecoder, BASE64Decoder

Constructor Summary

Constructors

Constructor and Description
CharacterDecoder()

Method Summary

Methods

Modifier and Type	Method and Description
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(java.io.PushbackInputStream aStream, java.io.OutputStream bStream, int l) This method does an actual decode.
byte[]	decodeBuffer(java.io.InputStream in) Decode the contents of the inputstream into a buffer.
void	decodeBuffer(java.io.InputStream aStream, java.io.OutputStream bStream) Decode the text from the InputStream and write the decoded octets to the OutputStream.
byte[]	decodeBuffer(java.lang.String inputString) Alternate decode interface that takes a String containing the encoded buffer and returns a byte array containing the data.
protected void	decodeBufferPrefix(java.io.PushbackInputStream aStream, java.io.OutputStream bStream) decode the beginning of the buffer, by default this is a NOP.
protected void	decodeBufferSuffix(java.io.PushbackInputStream aStream, java.io.OutputStream bStream) decode the buffer suffix, again by default it is a NOP.
java.nio.ByteBuffer	decodeBufferToByteBuffer(java.io.InputStream in) Decode the contents of the inputStream into a ByteBuffer.
java.nio.ByteBuffer	decodeBufferToByteBuffer(java.lang.String inputString) Decode the contents of the String into a ByteBuffer.
protected int	decodeLinePrefix(java.io.PushbackInputStream aStream, java.io.OutputStream bStream) This method should return, if it knows, the number of bytes that will be decoded.
protected void	decodeLineSuffix(java.io.PushbackInputStream aStream, java.io.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.
protected int	readFully(java.io.InputStream in, byte[] buffer, int offset, int len) This method works around the bizarre semantics of BufferedInputStream's read method.

Methods inherited from class java.lang.Object

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

Constructor Detail

CharacterDecoder

public CharacterDecoder()

Method Detail

bytesPerAtom

protected abstract int bytesPerAtom()

Return the number of bytes per atom of decoding

bytesPerLine

protected abstract int bytesPerLine()

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

decodeBufferPrefix

protected void decodeBufferPrefix(java.io.PushbackInputStream aStream,
                      java.io.OutputStream bStream)
                           throws java.io.IOException

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

Throws:

java.io.IOException

decodeBufferSuffix

protected void decodeBufferSuffix(java.io.PushbackInputStream aStream,
                      java.io.OutputStream bStream)
                           throws java.io.IOException

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

Throws:

java.io.IOException

decodeLinePrefix

protected int decodeLinePrefix(java.io.PushbackInputStream aStream,
                   java.io.OutputStream bStream)
                        throws java.io.IOException

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:

java.io.IOException

decodeLineSuffix

protected void decodeLineSuffix(java.io.PushbackInputStream aStream,
                    java.io.OutputStream bStream)
                         throws java.io.IOException

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:

java.io.IOException

decodeAtom

protected void decodeAtom(java.io.PushbackInputStream aStream,
              java.io.OutputStream bStream,
              int l)
                   throws java.io.IOException

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:

java.io.IOException

readFully

protected int readFully(java.io.InputStream in,
            byte[] buffer,
            int offset,
            int len)
                 throws java.io.IOException

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

Throws:

java.io.IOException

decodeBuffer

public void decodeBuffer(java.io.InputStream aStream,
                java.io.OutputStream bStream)
                  throws java.io.IOException

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

java.io.IOException

decodeBuffer

public byte[] decodeBuffer(java.lang.String inputString)
                    throws java.io.IOException

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

java.io.IOException

decodeBuffer

public byte[] decodeBuffer(java.io.InputStream in)
                    throws java.io.IOException

Decode the contents of the inputstream into a buffer.

Throws:

java.io.IOException

decodeBufferToByteBuffer

public java.nio.ByteBuffer decodeBufferToByteBuffer(java.lang.String inputString)
                                             throws java.io.IOException

Decode the contents of the String into a ByteBuffer.

Throws:

java.io.IOException

decodeBufferToByteBuffer

public java.nio.ByteBuffer decodeBufferToByteBuffer(java.io.InputStream in)
                                             throws java.io.IOException

Decode the contents of the inputStream into a ByteBuffer.

Throws:

java.io.IOException