ORG.oclc.ecat.util
Class CharacterDecoder

java.lang.Object
  |
  +--ORG.oclc.ecat.util.CharacterDecoder

Direct Known Subclasses:

BASE64Decoder, UCDecoder, UUDecoder

public abstract class CharacterDecoder

extends 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.

See Also:

CEFormatException, CharacterEncoder, UCDecoder, UUDecoder, BASE64Decoder

Constructor Summary

CharacterDecoder()

Method Summary

byte[]	decodeBuffer(InputStream in) Decode the contents of the inputstream into a buffer.
void	decodeBuffer(InputStream aStream, OutputStream bStream) Decode the text from the InputStream and write the decoded octets to the OutputStream.
byte[]	decodeBuffer(String inputString) Alternate decode interface that takes a String containing the encoded buffer and returns a byte array containing the data.
protected int	readFully(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

readFully

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

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

decodeBuffer

public void decodeBuffer(InputStream aStream,
                         OutputStream bStream)
                  throws 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

decodeBuffer

public byte[] decodeBuffer(String inputString)
                    throws 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

decodeBuffer

public byte[] decodeBuffer(InputStream in)
                    throws IOException

Decode the contents of the inputstream into a buffer.