Java example source code file (UnicodeDecoder.java)

This example Java source code file (UnicodeDecoder.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

big, byte_order_mark, charbuffer, charsetdecoder, coderresult, little, nio, none, reversed_mark, unicodedecoder

The UnicodeDecoder.java Java example source code

/*
 * Copyright (c) 2000, 2006, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.nio.cs;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.MalformedInputException;


abstract class UnicodeDecoder extends CharsetDecoder {

    protected static final char BYTE_ORDER_MARK = (char) 0xfeff;
    protected static final char REVERSED_MARK = (char) 0xfffe;

    protected static final int NONE = 0;
    protected static final int BIG = 1;
    protected static final int LITTLE = 2;

    private final int expectedByteOrder;
    private int currentByteOrder;
    private int defaultByteOrder = BIG;

    public UnicodeDecoder(Charset cs, int bo) {
        super(cs, 0.5f, 1.0f);
        expectedByteOrder = currentByteOrder = bo;
    }

    public UnicodeDecoder(Charset cs, int bo, int defaultBO) {
        this(cs, bo);
        defaultByteOrder = defaultBO;
    }

    private char decode(int b1, int b2) {
        if (currentByteOrder == BIG)
            return (char)((b1 << 8) | b2);
        else
            return (char)((b2 << 8) | b1);
    }

    protected CoderResult decodeLoop(ByteBuffer src, CharBuffer dst) {
        int mark = src.position();

        try {
            while (src.remaining() > 1) {
                int b1 = src.get() & 0xff;
                int b2 = src.get() & 0xff;

                // Byte Order Mark interpretation
                if (currentByteOrder == NONE) {
                    char c = (char)((b1 << 8) | b2);
                    if (c == BYTE_ORDER_MARK) {
                        currentByteOrder = BIG;
                        mark += 2;
                        continue;
                    } else if (c == REVERSED_MARK) {
                        currentByteOrder = LITTLE;
                        mark += 2;
                        continue;
                    } else {
                        currentByteOrder = defaultByteOrder;
                        // FALL THROUGH to process b1, b2 normally
                    }
                }

                char c = decode(b1, b2);

                if (c == REVERSED_MARK) {
                    // A reversed BOM cannot occur within middle of stream
                    return CoderResult.malformedForLength(2);
                }

                // Surrogates
                if (Character.isSurrogate(c)) {
                    if (Character.isHighSurrogate(c)) {
                        if (src.remaining() < 2)
                            return CoderResult.UNDERFLOW;
                        char c2 = decode(src.get() & 0xff, src.get() & 0xff);
                        if (!Character.isLowSurrogate(c2))
                            return CoderResult.malformedForLength(4);
                        if (dst.remaining() < 2)
                            return CoderResult.OVERFLOW;
                        mark += 4;
                        dst.put(c);
                        dst.put(c2);
                        continue;
                    }
                    // Unpaired low surrogate
                    return CoderResult.malformedForLength(2);
                }

                if (!dst.hasRemaining())
                    return CoderResult.OVERFLOW;
                mark += 2;
                dst.put(c);

            }
            return CoderResult.UNDERFLOW;

        } finally {
            src.position(mark);
        }
    }

    protected void implReset() {
        currentByteOrder = expectedByteOrder;
    }

}