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Java example source code file (ReaderUTF8.java)

This example Java source code file (ReaderUTF8.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

inputstream, ioexception, readerutf8, ucs-4, unsupportedencodingexception, utf\-32

The ReaderUTF8.java Java example source code

/*
 * Copyright (c) 2012, 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 jdk.internal.util.xml.impl;

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

/**
 * UTF-8 transformed UCS-2 character stream reader.
 *
 * This reader converts UTF-8 transformed UCS-2 characters to Java characters.
 * The UCS-2 subset of UTF-8 transformation is described in RFC-2279 #2
 * "UTF-8 definition":
 *  0000 0000-0000 007F   0xxxxxxx
 *  0000 0080-0000 07FF   110xxxxx 10xxxxxx
 *  0000 0800-0000 FFFF   1110xxxx 10xxxxxx 10xxxxxx
 *
 * This reader will return incorrect last character on broken UTF-8 stream.
 */
public class ReaderUTF8 extends Reader {

    private InputStream is;

    /**
     * Constructor.
     *
     * @param is A byte input stream.
     */
    public ReaderUTF8(InputStream is) {
        this.is = is;
    }

    /**
     * Reads characters into a portion of an array.
     *
     * @param cbuf Destination buffer.
     * @param off Offset at which to start storing characters.
     * @param len Maximum number of characters to read.
     * @exception IOException If any IO errors occur.
     * @exception UnsupportedEncodingException If UCS-4 character occur in the stream.
     */
    public int read(char[] cbuf, int off, int len) throws IOException {
        int num = 0;
        int val;
        while (num < len) {
            if ((val = is.read()) < 0) {
                return (num != 0) ? num : -1;
            }
            switch (val & 0xf0) {
                case 0xc0:
                case 0xd0:
                    cbuf[off++] = (char) (((val & 0x1f) << 6) | (is.read() & 0x3f));
                    break;

                case 0xe0:
                    cbuf[off++] = (char) (((val & 0x0f) << 12)
                            | ((is.read() & 0x3f) << 6) | (is.read() & 0x3f));
                    break;

                case 0xf0:      // UCS-4 character
                    throw new UnsupportedEncodingException("UTF-32 (or UCS-4) encoding not supported.");

                default:
                    cbuf[off++] = (char) val;
                    break;
            }
            num++;
        }
        return num;
    }

    /**
     * Reads a single character.
     *
     * @return 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.
     * @exception IOException If any IO errors occur.
     * @exception UnsupportedEncodingException If UCS-4 character occur in the stream.
     */
    public int read() throws IOException {
        int val;
        if ((val = is.read()) < 0) {
            return -1;
        }
        switch (val & 0xf0) {
            case 0xc0:
            case 0xd0:
                val = ((val & 0x1f) << 6) | (is.read() & 0x3f);
                break;

            case 0xe0:
                val = ((val & 0x0f) << 12)
                        | ((is.read() & 0x3f) << 6) | (is.read() & 0x3f);
                break;

            case 0xf0:  // UCS-4 character
                throw new UnsupportedEncodingException();

            default:
                break;
        }
        return val;
    }

    /**
     * Closes the stream.
     *
     * @exception IOException If any IO errors occur.
     */
    public void close() throws IOException {
        is.close();
    }
}

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