charsetdecoder.java

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    /**
     * Flushes this decoder.
     *
     * <p> The default implementation of this method does nothing, and always
     * returns {@link CoderResult#UNDERFLOW}.  This method should be overridden
     * by decoders that may need to write final characters to the output buffer
     * once the entire input sequence has been read. </p>
     *
     * @param  out
     *         The output character buffer
     *
     * @return  A coder-result object, either {@link CoderResult#UNDERFLOW} or
     *          {@link CoderResult#OVERFLOW}
     */
    protected CoderResult implFlush(CharBuffer out) {
	return CoderResult.UNDERFLOW;
    }

    /**
     * Resets this decoder, clearing any internal state.
     *
     * <p> This method resets charset-independent state and also invokes the
     * {@link #implReset() implReset} method in order to perform any
     * charset-specific reset actions.  </p>
     *
     * @return  This decoder
     *
     */
    public final CharsetDecoder reset() {
	implReset();
	state = ST_RESET;
	return this;
    }

    /**
     * Resets this decoder, clearing any charset-specific internal state.
     *
     * <p> The default implementation of this method does nothing.  This method
     * should be overridden by decoders that maintain internal state.  </p>
     */
    protected void implReset() { }

    /**
     * Decodes one or more bytes into one or more characters.
     *
     * <p> This method encapsulates the basic decoding loop, decoding as many
     * bytes as possible until it either runs out of input, runs out of room
     * in the output buffer, or encounters a decoding error.  This method is
     * invoked by the {@link #decode decode} method, which handles result
     * interpretation and error recovery.
     *
     * <p> The buffers are read from, and written to, starting at their current
     * positions.  At most {@link Buffer#remaining in.remaining()} bytes
     * will be read, and at most {@link Buffer#remaining out.remaining()}
     * characters will be written.  The buffers' positions will be advanced to
     * reflect the bytes read and the characters written, but their marks and
     * limits will not be modified.
     *
     * <p> This method returns a {@link CoderResult} object to describe its
     * reason for termination, in the same manner as the {@link #decode decode}
     * method.  Most implementations of this method will handle decoding errors
     * by returning an appropriate result object for interpretation by the
     * {@link #decode decode} method.  An optimized implementation may instead
     * examine the relevant error action and implement that action itself.
     *
     * <p> An implementation of this method may perform arbitrary lookahead by
     * returning {@link CoderResult#UNDERFLOW} until it receives sufficient
     * input.  </p>
     *
     * @param  in
     *         The input byte buffer
     *
     * @param  out
     *         The output character buffer
     *
     * @return  A coder-result object describing the reason for termination
     */
    protected abstract CoderResult decodeLoop(ByteBuffer in,
					      CharBuffer out);

    /**
     * Convenience method that decodes the remaining content of a single input
     * byte buffer into a newly-allocated character buffer.
     *
     * <p> This method implements an entire <a href="#steps">decoding
     * operation</a>; that is, it resets this decoder, then it decodes the
     * bytes in the given byte buffer, and finally it flushes this
     * decoder.  This method should therefore not be invoked if a decoding
     * operation is already in progress.  </p>
     *
     * @param  in
     *         The input byte buffer
     *
     * @return A newly-allocated character buffer containing the result of the
     *         decoding operation.  The buffer's position will be zero and its
     *         limit will follow the last character written.
     *
     * @throws  IllegalStateException
     *          If a decoding operation is already in progress
     *
     * @throws  MalformedInputException
     *          If the byte sequence starting at the input buffer's current
     *          position is not legal for this charset and the current malformed-input action
     *          is {@link CodingErrorAction#REPORT}
     *
     * @throws  UnmappableCharacterException
     *          If the byte sequence starting at the input buffer's current
     *          position cannot be mapped to an equivalent character sequence and
     *          the current unmappable-character action is {@link
     *          CodingErrorAction#REPORT}
     */
    public final CharBuffer decode(ByteBuffer in)
	throws CharacterCodingException
    {
	int n = (int)(in.remaining() * averageCharsPerByte());
	CharBuffer out = CharBuffer.allocate(n);

	if (n == 0)
	    return out;
	reset();
	for (;;) {
	    CoderResult cr;
	    if (in.hasRemaining())
		cr = decode(in, out, true);
	    else
		cr = flush(out);
	    if (cr.isUnderflow())
		break;
	    if (cr.isOverflow()) {
		n *= 2;
		CharBuffer o = CharBuffer.allocate(n);
		out.flip();
		o.put(out);
		out = o;
		continue;
	    }
	    cr.throwException();
	}
	out.flip();
	return out;
    }



    /**
     * Tells whether or not this decoder implements an auto-detecting charset.
     *
     * <p> The default implementation of this method always returns
     * <tt>false</tt>; it should be overridden by auto-detecting decoders to
     * return <tt>true</tt>.  </p>
     *
     * @return  <tt>true</tt> if, and only if, this decoder implements an
     *          auto-detecting charset
     */
    public boolean isAutoDetecting() {
	return false;
    }

    /**
     * Tells whether or not this decoder has yet detected a
     * charset&nbsp;&nbsp;<i>(optional operation)</i>.
     *
     * <p> If this decoder implements an auto-detecting charset then at a
     * single point during a decoding operation this method may start returning
     * <tt>true</tt> to indicate that a specific charset has been detected in
     * the input byte sequence.  Once this occurs, the {@link #detectedCharset
     * detectedCharset} method may be invoked to retrieve the detected charset.
     *
     * <p> That this method returns <tt>false</tt> does not imply that no bytes
     * have yet been decoded.  Some auto-detecting decoders are capable of
     * decoding some, or even all, of an input byte sequence without fixing on
     * a particular charset.
     *
     * <p> The default implementation of this method always throws an {@link
     * UnsupportedOperationException}; it should be overridden by
     * auto-detecting decoders to return <tt>true</tt> once the input charset
     * has been determined.  </p>
     *
     * @return  <tt>true</tt> if, and only if, this decoder has detected a
     *          specific charset
     *
     * @throws  UnsupportedOperationException
     *          If this decoder does not implement an auto-detecting charset
     */
    public boolean isCharsetDetected() {
	throw new UnsupportedOperationException();
    }

    /**
     * Retrieves the charset that was detected by this
     * decoder&nbsp;&nbsp;<i>(optional operation)</i>.
     *
     * <p> If this decoder implements an auto-detecting charset then this
     * method returns the actual charset once it has been detected.  After that
     * point, this method returns the same value for the duration of the
     * current decoding operation.  If not enough input bytes have yet been
     * read to determine the actual charset then this method throws an {@link
     * IllegalStateException}.
     *
     * <p> The default implementation of this method always throws an {@link
     * UnsupportedOperationException}; it should be overridden by
     * auto-detecting decoders to return the appropriate value.  </p>
     *
     * @return  The charset detected by this auto-detecting decoder,
     *          or <tt>null</tt> if the charset has not yet been determined
     *
     * @throws  IllegalStateException
     *          If insufficient bytes have been read to determine a charset
     *
     * @throws  UnsupportedOperationException
     *          If this decoder does not implement an auto-detecting charset
     */
    public Charset detectedCharset() {
	throw new UnsupportedOperationException();
    }


























































































    private void throwIllegalStateException(int from, int to) {
	throw new IllegalStateException("Current state = " + stateNames[from]
					+ ", new state = " + stateNames[to]);
    }

}