java/15 : java.xml/com/sun/org/apache/xerces/internal/impl/io/UTF8Reader.java

UTF8Reader
https://openjdk.java.net/
GPLv2 + Classpath Exception
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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,
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package com.sun.org.apache.xerces.internal.impl.io;

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

import java.util.Locale;
import com.sun.org.apache.xerces.internal.util.MessageFormatter;
import com.sun.org.apache.xerces.internal.impl.msg.XMLMessageFormatter;

import com.sun.xml.internal.stream.util.BufferAllocator;
import com.sun.xml.internal.stream.util.ThreadLocalBufferAllocator;

A UTF-8 reader.
Author: Andy Clark, IBM
@xerces.internal /**
 * <p>A UTF-8 reader.</p>
 *
 * @xerces.internal
 *
 * @author Andy Clark, IBM
 *
 */
public class UTF8Reader
    extends Reader {

    //
    // Constants
    //

    Default byte buffer size (2048). /** Default byte buffer size (2048). */
    public static final int DEFAULT_BUFFER_SIZE = 2048;

    // debugging

    Debug read. /** Debug read. */
    private static final boolean DEBUG_READ = false;

    //
    // Data
    //

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

    Byte buffer. /** Byte buffer. */
    protected byte[] fBuffer;

    Offset into buffer. /** Offset into buffer. */
    protected int fOffset;

    Surrogate character. /** Surrogate character. */
    private int fSurrogate = -1;

    // message formatter; used to produce localized
    // exception messages
    private MessageFormatter fFormatter = null;

    //Locale to use for messages
    private Locale fLocale = null;

    //
    // Constructors
    //

    Constructs a UTF-8 reader from the specified input stream
using the default buffer size.  Primarily for testing.
Params: inputStream – The input stream./**
     * Constructs a UTF-8 reader from the specified input stream
     * using the default buffer size.  Primarily for testing.
     *
     * @param inputStream The input stream.
     */
    public UTF8Reader(InputStream inputStream) {
        this(inputStream, DEFAULT_BUFFER_SIZE, new XMLMessageFormatter(), Locale.getDefault());
    } // <init>(InputStream, MessageFormatter)

    Constructs a UTF-8 reader from the specified input stream
using the default buffer size and the given MessageFormatter.
Params: inputStream – The input stream.
messageFormatter –  given MessageFormatter
locale –    Locale to use for messages/**
     * Constructs a UTF-8 reader from the specified input stream
     * using the default buffer size and the given MessageFormatter.
     *
     * @param inputStream The input stream.
     * @param messageFormatter  given MessageFormatter
     * @param locale    Locale to use for messages
     */
    public UTF8Reader(InputStream inputStream, MessageFormatter messageFormatter,
            Locale locale) {
        this(inputStream, DEFAULT_BUFFER_SIZE, messageFormatter, locale);
    } // <init>(InputStream, MessageFormatter, Locale)

    Constructs a UTF-8 reader from the specified input stream,
buffer size and MessageFormatter.
Params: inputStream – The input stream.
size –        The initial buffer size.
messageFormatter –  the formatter for localizing/formatting errors.
locale –    the Locale to use for messages/**
     * Constructs a UTF-8 reader from the specified input stream,
     * buffer size and MessageFormatter.
     *
     * @param inputStream The input stream.
     * @param size        The initial buffer size.
     * @param messageFormatter  the formatter for localizing/formatting errors.
     * @param locale    the Locale to use for messages
     */
    public UTF8Reader(InputStream inputStream, int size,
            MessageFormatter messageFormatter, Locale locale) {
        fInputStream = inputStream;
        BufferAllocator ba = ThreadLocalBufferAllocator.getBufferAllocator();
        fBuffer = ba.getByteBuffer(size);
        if (fBuffer == null) {
            fBuffer = new byte[size];
        }
        fFormatter = messageFormatter;
        fLocale = locale;
    } // <init>(InputStream, int, 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 16383
            (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 16383
     *             (<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 {

        // decode character
        int c = fSurrogate;
        if (fSurrogate == -1) {
            // NOTE: We use the index into the buffer if there are remaining
            //       bytes from the last block read. -Ac
            int index = 0;

            // get first byte
            int b0 = index == fOffset
                   ? fInputStream.read() : fBuffer[index++] & 0x00FF;
            if (b0 == -1) {
                return -1;
            }

            // UTF-8:   [0xxx xxxx]
            // Unicode: [0000 0000] [0xxx xxxx]
            if (b0 < 0x80) {
                c = (char)b0;
            }

            // UTF-8:   [110y yyyy] [10xx xxxx]
            // Unicode: [0000 0yyy] [yyxx xxxx]
            else if ((b0 & 0xE0) == 0xC0 && (b0 & 0x1E) != 0) {
                int b1 = index == fOffset
                       ? fInputStream.read() : fBuffer[index++] & 0x00FF;
                if (b1 == -1) {
                    expectedByte(2, 2);
                }
                if ((b1 & 0xC0) != 0x80) {
                    invalidByte(2, 2, b1);
                }
                c = ((b0 << 6) & 0x07C0) | (b1 & 0x003F);
            }

            // UTF-8:   [1110 zzzz] [10yy yyyy] [10xx xxxx]
            // Unicode: [zzzz yyyy] [yyxx xxxx]
            else if ((b0 & 0xF0) == 0xE0) {
                int b1 = index == fOffset
                       ? fInputStream.read() : fBuffer[index++] & 0x00FF;
                if (b1 == -1) {
                    expectedByte(2, 3);
                }
                if ((b1 & 0xC0) != 0x80
                    || (b0 == 0xED && b1 >= 0xA0)
                    || ((b0 & 0x0F) == 0 && (b1 & 0x20) == 0)) {
                    invalidByte(2, 3, b1);
                }
                int b2 = index == fOffset
                       ? fInputStream.read() : fBuffer[index++] & 0x00FF;
                if (b2 == -1) {
                    expectedByte(3, 3);
                }
                if ((b2 & 0xC0) != 0x80) {
                    invalidByte(3, 3, b2);
                }
                c = ((b0 << 12) & 0xF000) | ((b1 << 6) & 0x0FC0) |
                    (b2 & 0x003F);
            }

            // UTF-8:   [1111 0uuu] [10uu zzzz] [10yy yyyy] [10xx xxxx]*
            // Unicode: [1101 10ww] [wwzz zzyy] (high surrogate)
            //          [1101 11yy] [yyxx xxxx] (low surrogate)
            //          * uuuuu = wwww + 1
            else if ((b0 & 0xF8) == 0xF0) {
                int b1 = index == fOffset
                       ? fInputStream.read() : fBuffer[index++] & 0x00FF;
                if (b1 == -1) {
                    expectedByte(2, 4);
                }
                if ((b1 & 0xC0) != 0x80
                    || ((b1 & 0x30) == 0 && (b0 & 0x07) == 0)) {
                    invalidByte(2, 3, b1);
                }
                int b2 = index == fOffset
                       ? fInputStream.read() : fBuffer[index++] & 0x00FF;
                if (b2 == -1) {
                    expectedByte(3, 4);
                }
                if ((b2 & 0xC0) != 0x80) {
                    invalidByte(3, 3, b2);
                }
                int b3 = index == fOffset
                       ? fInputStream.read() : fBuffer[index++] & 0x00FF;
                if (b3 == -1) {
                    expectedByte(4, 4);
                }
                if ((b3 & 0xC0) != 0x80) {
                    invalidByte(4, 4, b3);
                }
                int uuuuu = ((b0 << 2) & 0x001C) | ((b1 >> 4) & 0x0003);
                if (uuuuu > 0x10) {
                    invalidSurrogate(uuuuu);
                }
                int wwww = uuuuu - 1;
                int hs = 0xD800 |
                         ((wwww << 6) & 0x03C0) | ((b1 << 2) & 0x003C) |
                         ((b2 >> 4) & 0x0003);
                int ls = 0xDC00 | ((b2 << 6) & 0x03C0) | (b3 & 0x003F);
                c = hs;
                fSurrogate = ls;
            }

            // error
            else {
                invalidByte(1, 1, b0);
            }
        }

        // use surrogate
        else {
            fSurrogate = -1;
        }

        // return character
        if (DEBUG_READ) {
            System.out.println("read(): 0x"+Integer.toHexString(c));
        }
        return c;

    } // 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 {

        // handle surrogate
        int out = offset;
        if (fSurrogate != -1) {
            ch[offset + 1] = (char)fSurrogate;
            fSurrogate = -1;
            length--;
            out++;
        }

        // read bytes
        int count = 0;
        if (fOffset == 0) {
            // adjust length to read
            if (length > fBuffer.length) {
                length = fBuffer.length;
            }

            // perform read operation
            count = fInputStream.read(fBuffer, 0, length);
            if (count == -1) {
                return -1;
            }
            count += out - offset;
        }

        // skip read; last character was in error
        // NOTE: Having an offset value other than zero means that there was
        //       an error in the last character read. In this case, we have
        //       skipped the read so we don't consume any bytes past the
        //       error. By signalling the error on the next block read we
        //       allow the method to return the most valid characters that
        //       it can on the previous block read. -Ac
        else {
            count = fOffset;
            fOffset = 0;
        }

        // convert bytes to characters
        final int total = count;
        int in;
        byte byte1;
        final byte byte0 = 0;
        for (in = 0; in < total; in++) {
            byte1 = fBuffer[in];
            if (byte1 >= byte0) {
                ch[out++] = (char)byte1;
            }
            else   {
                break;
            }
        }
        for ( ; in < total; in++) {
            byte1 = fBuffer[in];

            // UTF-8:   [0xxx xxxx]
            // Unicode: [0000 0000] [0xxx xxxx]
            if (byte1 >= byte0) {
                ch[out++] = (char)byte1;
                continue;
            }

            // UTF-8:   [110y yyyy] [10xx xxxx]
            // Unicode: [0000 0yyy] [yyxx xxxx]
            int b0 = byte1 & 0x0FF;
            if ((b0 & 0xE0) == 0xC0 && (b0 & 0x1E) != 0) {
                int b1 = -1;
                if (++in < total) {
                    b1 = fBuffer[in] & 0x00FF;
                }
                else {
                    b1 = fInputStream.read();
                    if (b1 == -1) {
                        if (out > offset) {
                            fBuffer[0] = (byte)b0;
                            fOffset = 1;
                            return out - offset;
                        }
                        expectedByte(2, 2);
                    }
                    count++;
                }
                if ((b1 & 0xC0) != 0x80) {
                    if (out > offset) {
                        fBuffer[0] = (byte)b0;
                        fBuffer[1] = (byte)b1;
                        fOffset = 2;
                        return out - offset;
                    }
                    invalidByte(2, 2, b1);
                }
                int c = ((b0 << 6) & 0x07C0) | (b1 & 0x003F);
                ch[out++] = (char)c;
                count -= 1;
                continue;
            }

            // UTF-8:   [1110 zzzz] [10yy yyyy] [10xx xxxx]
            // Unicode: [zzzz yyyy] [yyxx xxxx]
            if ((b0 & 0xF0) == 0xE0) {
                int b1 = -1;
                if (++in < total) {
                    b1 = fBuffer[in] & 0x00FF;
                }
                else {
                    b1 = fInputStream.read();
                    if (b1 == -1) {
                        if (out > offset) {
                            fBuffer[0] = (byte)b0;
                            fOffset = 1;
                            return out - offset;
                        }
                        expectedByte(2, 3);
                    }
                    count++;
                }
                if ((b1 & 0xC0) != 0x80
                    || (b0 == 0xED && b1 >= 0xA0)
                    || ((b0 & 0x0F) == 0 && (b1 & 0x20) == 0)) {
                    if (out > offset) {
                        fBuffer[0] = (byte)b0;
                        fBuffer[1] = (byte)b1;
                        fOffset = 2;
                        return out - offset;
                    }
                    invalidByte(2, 3, b1);
                }
                int b2 = -1;
                if (++in < total) {
                    b2 = fBuffer[in] & 0x00FF;
                }
                else {
                    b2 = fInputStream.read();
                    if (b2 == -1) {
                        if (out > offset) {
                            fBuffer[0] = (byte)b0;
                            fBuffer[1] = (byte)b1;
                            fOffset = 2;
                            return out - offset;
                        }
                        expectedByte(3, 3);
                    }
                    count++;
                }
                if ((b2 & 0xC0) != 0x80) {
                    if (out > offset) {
                        fBuffer[0] = (byte)b0;
                        fBuffer[1] = (byte)b1;
                        fBuffer[2] = (byte)b2;
                        fOffset = 3;
                        return out - offset;
                    }
                    invalidByte(3, 3, b2);
                }
                int c = ((b0 << 12) & 0xF000) | ((b1 << 6) & 0x0FC0) |
                        (b2 & 0x003F);
                ch[out++] = (char)c;
                count -= 2;
                continue;
            }

            // UTF-8:   [1111 0uuu] [10uu zzzz] [10yy yyyy] [10xx xxxx]*
            // Unicode: [1101 10ww] [wwzz zzyy] (high surrogate)
            //          [1101 11yy] [yyxx xxxx] (low surrogate)
            //          * uuuuu = wwww + 1
            if ((b0 & 0xF8) == 0xF0) {
                int b1 = -1;
                if (++in < total) {
                    b1 = fBuffer[in] & 0x00FF;
                }
                else {
                    b1 = fInputStream.read();
                    if (b1 == -1) {
                        if (out > offset) {
                            fBuffer[0] = (byte)b0;
                            fOffset = 1;
                            return out - offset;
                        }
                        expectedByte(2, 4);
                    }
                    count++;
                }
                if ((b1 & 0xC0) != 0x80
                    || ((b1 & 0x30) == 0 && (b0 & 0x07) == 0)) {
                    if (out > offset) {
                        fBuffer[0] = (byte)b0;
                        fBuffer[1] = (byte)b1;
                        fOffset = 2;
                        return out - offset;
                    }
                    invalidByte(2, 4, b1);
                }
                int b2 = -1;
                if (++in < total) {
                    b2 = fBuffer[in] & 0x00FF;
                }
                else {
                    b2 = fInputStream.read();
                    if (b2 == -1) {
                        if (out > offset) {
                            fBuffer[0] = (byte)b0;
                            fBuffer[1] = (byte)b1;
                            fOffset = 2;
                            return out - offset;
                        }
                        expectedByte(3, 4);
                    }
                    count++;
                }
                if ((b2 & 0xC0) != 0x80) {
                    if (out > offset) {
                        fBuffer[0] = (byte)b0;
                        fBuffer[1] = (byte)b1;
                        fBuffer[2] = (byte)b2;
                        fOffset = 3;
                        return out - offset;
                    }
                    invalidByte(3, 4, b2);
                }
                int b3 = -1;
                if (++in < total) {
                    b3 = fBuffer[in] & 0x00FF;
                }
                else {
                    b3 = fInputStream.read();
                    if (b3 == -1) {
                        if (out > offset) {
                            fBuffer[0] = (byte)b0;
                            fBuffer[1] = (byte)b1;
                            fBuffer[2] = (byte)b2;
                            fOffset = 3;
                            return out - offset;
                        }
                        expectedByte(4, 4);
                    }
                    count++;
                }
                if ((b3 & 0xC0) != 0x80) {
                    if (out > offset) {
                        fBuffer[0] = (byte)b0;
                        fBuffer[1] = (byte)b1;
                        fBuffer[2] = (byte)b2;
                        fBuffer[3] = (byte)b3;
                        fOffset = 4;
                        return out - offset;
                    }
                    invalidByte(4, 4, b2);
                }

                // check if output buffer is large enough to hold 2 surrogate chars
                if (out + 1 >= ch.length) {
                    fBuffer[0] = (byte)b0;
                    fBuffer[1] = (byte)b1;
                    fBuffer[2] = (byte)b2;
                    fBuffer[3] = (byte)b3;
                    fOffset = 4;
                    return out - offset;
                }

                // decode bytes into surrogate characters
                int uuuuu = ((b0 << 2) & 0x001C) | ((b1 >> 4) & 0x0003);
                if (uuuuu > 0x10) {
                    invalidSurrogate(uuuuu);
                }
                int wwww = uuuuu - 1;
                int zzzz = b1 & 0x000F;
                int yyyyyy = b2 & 0x003F;
                int xxxxxx = b3 & 0x003F;
                int hs = 0xD800 | ((wwww << 6) & 0x03C0) | (zzzz << 2) | (yyyyyy >> 4);
                int ls = 0xDC00 | ((yyyyyy << 6) & 0x03C0) | xxxxxx;

                // set characters
                ch[out++] = (char)hs;
                ch[out++] = (char)ls;
                count -= 2;
                continue;
            }

            // error
            if (out > offset) {
                fBuffer[0] = (byte)b0;
                fOffset = 1;
                return out - offset;
            }
            invalidByte(1, 1, b0);
        }

        // return number of characters converted
        if (DEBUG_READ) {
            System.out.println("read(char[],"+offset+','+length+"): count="+count);
        }
        return count;

    } // 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 remaining = n;
        final char[] ch = new char[fBuffer.length];
        do {
            int length = ch.length < remaining ? ch.length : (int)remaining;
            int count = read(ch, 0, length);
            if (count > 0) {
                remaining -= count;
            }
            else {
                break;
            }
        } while (remaining > 0);

        long skipped = n - remaining;
        return skipped;

    } // 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-8"}));
    } // 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 {
        fOffset = 0;
        fSurrogate = -1;
    } // 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 {
        BufferAllocator ba = ThreadLocalBufferAllocator.getBufferAllocator();
        ba.returnByteBuffer(fBuffer);
        fBuffer = null;
        fInputStream.close();
    } // close()

    //
    // Private methods
    //

    Throws an exception for expected byte. /** Throws an exception for expected byte. */
    private void expectedByte(int position, int count)
        throws MalformedByteSequenceException {

        throw new MalformedByteSequenceException(fFormatter,
            fLocale,
            XMLMessageFormatter.XML_DOMAIN,
            "ExpectedByte",
            new Object[] {Integer.toString(position), Integer.toString(count)});

    } // expectedByte(int,int)

    Throws an exception for invalid byte. /** Throws an exception for invalid byte. */
    private void invalidByte(int position, int count, int c)
        throws MalformedByteSequenceException {

        throw new MalformedByteSequenceException(fFormatter,
            fLocale,
            XMLMessageFormatter.XML_DOMAIN,
            "InvalidByte",
            new Object [] {Integer.toString(position), Integer.toString(count)});

    } // invalidByte(int,int,int)

    Throws an exception for invalid surrogate bits. /** Throws an exception for invalid surrogate bits. */
    private void invalidSurrogate(int uuuuu) throws MalformedByteSequenceException {

        throw new MalformedByteSequenceException(fFormatter,
            fLocale,
            XMLMessageFormatter.XML_DOMAIN,
            "InvalidHighSurrogate",
            new Object[] {Integer.toHexString(uuuuu)});

    } // invalidSurrogate(int)

} // class UTF8Reader
Throws:	IOException – If an I/O error occurs
Returns:	The character read, as an integer in the range 0 to 16383 (`0x00-0xffff`), or -1 if the end of the stream has been 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
Params:	n – The number of characters to skip
Throws:	IOException – If an I/O error occurs
Returns:	The number of characters actually skipped
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
/

java/ 15/ java.xml/com/sun/org/apache/xerces/internal/impl/io/UTF8Reader.java
