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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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package org.apache.xerces.impl.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Locale;

import org.apache.xerces.impl.msg.XMLMessageFormatter;
import org.apache.xerces.util.MessageFormatter;

A UTF-16 reader. Can also be used for UCS-2 (i.e. ISO-10646-UCS-2).
Author:
Michael Glavassevich, IBM
@xerces.internal
Version:
$Id: UTF16Reader.java 718095 2008-11-16 20:00:14Z mrglavas $/**
 * <p>A UTF-16 reader. Can also be used for UCS-2 (i.e. ISO-10646-UCS-2).</p>
 * 
 * @xerces.internal

 * 
 * @author Michael Glavassevich, IBM
 *
 * @version $Id: UTF16Reader.java 718095 2008-11-16 20:00:14Z mrglavas $
 */
public final class UTF16Reader 
    extends Reader {
    
    //
    // Constants
    //

    
Default byte buffer size (4096). /** Default byte buffer size (4096). */
    public static final int DEFAULT_BUFFER_SIZE = 4096;
    
    //
    // Data
    //

    
Input stream. /** Input stream. */
    protected final InputStream fInputStream;

    
Byte buffer. /** Byte buffer. */
    protected final byte[] fBuffer;
    
    
Endianness. /** Endianness. */
    protected final boolean fIsBigEndian;
    
    // message formatter; used to produce localized exception messages
    private final MessageFormatter fFormatter;

    // Locale to use for messages
    private final Locale fLocale;
    
    //
    // Constructors
    //

    
Constructs a UTF-16 reader from the specified input stream 
using the default buffer size. Primarily for testing.
Params:
inputStream – The input stream.
isBigEndian – The byte order./** 
     * Constructs a UTF-16 reader from the specified input stream 
     * using the default buffer size. Primarily for testing.
     *
     * @param inputStream The input stream.
     * @param isBigEndian The byte order.
     */
    public UTF16Reader(InputStream inputStream, boolean isBigEndian) {
        this(inputStream, DEFAULT_BUFFER_SIZE, isBigEndian, 
                new XMLMessageFormatter(), Locale.getDefault());
    } // <init>(InputStream, boolean)
    
    
Constructs a UTF-16 reader from the specified input stream 
using the default buffer size and the given MessageFormatter.
Params:
inputStream – The input stream.
isBigEndian – The byte order./** 
     * Constructs a UTF-16 reader from the specified input stream 
     * using the default buffer size and the given MessageFormatter.
     *
     * @param inputStream The input stream.
     * @param isBigEndian The byte order.
     */
    public UTF16Reader(InputStream inputStream, boolean isBigEndian, 
            MessageFormatter messageFormatter, Locale locale) {
        this(inputStream, DEFAULT_BUFFER_SIZE, isBigEndian, messageFormatter, locale);
    } // <init>(InputStream, boolean, MessageFormatter, Locale)
    
    
Constructs a UTF-16 reader from the specified input stream 
and buffer size and given MessageFormatter.
Params:
inputStream –       The input stream.
size –              The initial buffer size.
isBigEndian –       The byte order.
messageFormatter –  Given MessageFormatter
locale –            Locale to use for messages/** 
     * Constructs a UTF-16 reader from the specified input stream 
     * and buffer size and given MessageFormatter.
     *
     * @param inputStream       The input stream.
     * @param size              The initial buffer size.
     * @param isBigEndian       The byte order.
     * @param messageFormatter  Given MessageFormatter
     * @param locale            Locale to use for messages
     */
    public UTF16Reader(InputStream inputStream, int size, boolean isBigEndian, 
            MessageFormatter messageFormatter, Locale locale) {
        this(inputStream, new byte[size], isBigEndian, messageFormatter, locale);
    } // <init>(InputStream, int, boolean, MessageFormatter, Locale)
    
    
Constructs a UTF-16 reader from the specified input stream, 
buffer and MessageFormatter.
Params:
inputStream –       The input stream.
buffer –            The byte buffer.
isBigEndian –       The byte order.
messageFormatter –  Given MessageFormatter
locale –            Locale to use for messages/** 
     * Constructs a UTF-16 reader from the specified input stream, 
     * buffer and MessageFormatter.
     *
     * @param inputStream       The input stream.
     * @param buffer            The byte buffer.
     * @param isBigEndian       The byte order.
     * @param messageFormatter  Given MessageFormatter
     * @param locale            Locale to use for messages
     */
    public UTF16Reader(InputStream inputStream, byte [] buffer, boolean isBigEndian, 
            MessageFormatter messageFormatter, Locale locale) {
        fInputStream = inputStream;
        fBuffer = buffer;
        fIsBigEndian = isBigEndian;
        fFormatter = messageFormatter;
        fLocale = locale;
    } // <init>(InputStream, byte[], boolean, MessageFormatter, Locale)
    
    //
    // Reader methods
    //
    
    
Read a single character.  This method will block until a character is
available, an I/O error occurs, or the end of the stream is reached.
 Subclasses that intend to support efficient single-character input
should override this method.
Throws:
IOException –  If an I/O error occurs
Returns:
    The character read, as an integer in the range 0 to 65535
            (0x00-0xffff), or -1 if the end of the stream has
            been reached/**
     * Read a single character.  This method will block until a character is
     * available, an I/O error occurs, or the end of the stream is reached.
     *
     * <p> Subclasses that intend to support efficient single-character input
     * should override this method.
     *
     * @return     The character read, as an integer in the range 0 to 65535
     *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
     *             been reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read() throws IOException {
        final int b0 = fInputStream.read();
        if (b0 == -1) {
            return -1;
        }
        final int b1 = fInputStream.read();
        if (b1 == -1) {
            expectedTwoBytes();
        }
        // UTF-16BE
        if (fIsBigEndian) {
            return (b0 << 8) | b1;
        }
        // UTF-16LE
        return (b1 << 8) | b0;
    } // read():int

    
Read characters into a portion of an array.  This method will block
until some input is available, an I/O error occurs, or the end of the
stream is reached.
Params:
ch –     Destination buffer
offset – Offset at which to start storing characters
length – Maximum number of characters to read
Throws:
IOException –  If an I/O error occurs
Returns:
    The number of characters read, or -1 if the end of the
            stream has been reached/**
     * Read characters into a portion of an array.  This method will block
     * until some input is available, an I/O error occurs, or the end of the
     * stream is reached.
     *
     * @param      ch     Destination buffer
     * @param      offset Offset at which to start storing characters
     * @param      length Maximum number of characters to read
     *
     * @return     The number of characters read, or -1 if the end of the
     *             stream has been reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read(char ch[], int offset, int length) throws IOException {
        int byteLength = length << 1;
        if (byteLength > fBuffer.length) {
            byteLength = fBuffer.length;
        }
        int byteCount = fInputStream.read(fBuffer, 0, byteLength);
        if (byteCount == -1) {
            return -1;
        }
        // If an odd number of bytes were read, we still need to read one more.
        if ((byteCount & 1) != 0) {
            int b = fInputStream.read();
            if (b == -1) {
                expectedTwoBytes();
            }
            fBuffer[byteCount++] = (byte) b;
        }
        final int charCount = byteCount >> 1;
        if (fIsBigEndian) {
            processBE(ch, offset, charCount);
        }
        else {
            processLE(ch, offset, charCount);
        }
        return charCount;
    } // read(char[],int,int)

    
Skip characters.  This method will block until some characters are
available, an I/O error occurs, or the end of the stream is reached.
Params:
n –  The number of characters to skip
Throws:
IOException –  If an I/O error occurs
Returns:
   The number of characters actually skipped/**
     * Skip characters.  This method will block until some characters are
     * available, an I/O error occurs, or the end of the stream is reached.
     *
     * @param  n  The number of characters to skip
     *
     * @return    The number of characters actually skipped
     *
     * @exception  IOException  If an I/O error occurs
     */
    public long skip(long n) throws IOException {
        long bytesSkipped = fInputStream.skip(n << 1);
        if ((bytesSkipped & 1) != 0) {
            int b = fInputStream.read();
            if (b == -1) {
                expectedTwoBytes();
            }
            ++bytesSkipped;
        }
        return bytesSkipped >> 1;
    } // skip(long):long

    
Tell whether this stream is ready to be read.
Throws:
IOException –  If an I/O error occurs
Returns:
True if the next read() is guaranteed not to block for input,
false otherwise.  Note that returning false does not guarantee that the
next read will block./**
     * Tell whether this stream is ready to be read.
     *
     * @return True if the next read() is guaranteed not to block for input,
     * false otherwise.  Note that returning false does not guarantee that the
     * next read will block.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public boolean ready() throws IOException {
        return false;
    } // ready()

    
Tell whether this stream supports the mark() operation.
/**
     * Tell whether this stream supports the mark() operation.
     */
    public boolean markSupported() {
        return false;
    } // markSupported()

    
Mark the present position in the stream.  Subsequent calls to reset()
will attempt to reposition the stream to this point.  Not all
character-input streams support the mark() operation.
Params:
readAheadLimit –  Limit on the number of characters that may be
                        read while still preserving the mark.  After
                        reading this many characters, attempting to
                        reset the stream may fail.
Throws:
IOException –  If the stream does not support mark(),
                         or if some other I/O error occurs/**
     * Mark the present position in the stream.  Subsequent calls to reset()
     * will attempt to reposition the stream to this point.  Not all
     * character-input streams support the mark() operation.
     *
     * @param  readAheadLimit  Limit on the number of characters that may be
     *                         read while still preserving the mark.  After
     *                         reading this many characters, attempting to
     *                         reset the stream may fail.
     *
     * @exception  IOException  If the stream does not support mark(),
     *                          or if some other I/O error occurs
     */
    public void mark(int readAheadLimit) throws IOException {
        throw new IOException(fFormatter.formatMessage(fLocale, "OperationNotSupported", new Object[]{"mark()", "UTF-16"}));
    } // mark(int)

    
Reset the stream.  If the stream has been marked, then attempt to
reposition it at the mark.  If the stream has not been marked, then
attempt to reset it in some way appropriate to the particular stream,
for example by repositioning it to its starting point.  Not all
character-input streams support the reset() operation, and some support
reset() without supporting mark().
Throws:
IOException –  If the stream has not been marked,
                         or if the mark has been invalidated,
                         or if the stream does not support reset(),
                         or if some other I/O error occurs/**
     * Reset the stream.  If the stream has been marked, then attempt to
     * reposition it at the mark.  If the stream has not been marked, then
     * attempt to reset it in some way appropriate to the particular stream,
     * for example by repositioning it to its starting point.  Not all
     * character-input streams support the reset() operation, and some support
     * reset() without supporting mark().
     *
     * @exception  IOException  If the stream has not been marked,
     *                          or if the mark has been invalidated,
     *                          or if the stream does not support reset(),
     *                          or if some other I/O error occurs
     */
    public void reset() throws IOException {
    } // reset()

    
Close the stream.  Once a stream has been closed, further read(),
ready(), mark(), or reset() invocations will throw an IOException.
Closing a previously-closed stream, however, has no effect.
Throws:
IOException –  If an I/O error occurs/**
     * Close the stream.  Once a stream has been closed, further read(),
     * ready(), mark(), or reset() invocations will throw an IOException.
     * Closing a previously-closed stream, however, has no effect.
     *
     * @exception  IOException  If an I/O error occurs
     */
     public void close() throws IOException {
         fInputStream.close();
     } // close()
     
     //
     // Private methods
     //
     
     
Decodes UTF-16BE /** Decodes UTF-16BE **/
     private void processBE(final char ch[], int offset, final int count) {
         int curPos = 0;
         for (int i = 0; i < count; ++i) {
             final int b0 = fBuffer[curPos++] & 0xff;
             final int b1 = fBuffer[curPos++] & 0xff;
             ch[offset++] = (char) ((b0 << 8) | b1);
         }
     } // processBE(char[],int,int)
     
     
Decodes UTF-16LE /** Decodes UTF-16LE **/
     private void processLE(final char ch[], int offset, final int count) {
         int curPos = 0;
         for (int i = 0; i < count; ++i) {
             final int b0 = fBuffer[curPos++] & 0xff;
             final int b1 = fBuffer[curPos++] & 0xff;
             ch[offset++] = (char) ((b1 << 8) | b0);
         }
     } // processLE(char[],int,int)

     
Throws an exception for expected byte. /** Throws an exception for expected byte. */
     private void expectedTwoBytes()
         throws MalformedByteSequenceException {
         throw new MalformedByteSequenceException(fFormatter,
             fLocale,
             XMLMessageFormatter.XML_DOMAIN,
             "ExpectedByte",
             new Object[] {"2", "2"});
     } // expectedTwoBytes()

} // class UTF16Reader