singlebytecharsetconverter.java

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/*
 Copyright (C) 2002-2004 MySQL AB

 This program is free software; you can redistribute it and/or modify
 it under the terms of version 2 of the GNU General Public License as
 published by the Free Software Foundation.
 

 There are special exceptions to the terms and conditions of the GPL 
 as it is applied to this software. View the full text of the 
 exception exception in file EXCEPTIONS-CONNECTOR-J in the directory of this 
 software distribution.

 This program 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 for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */
package com.mysql.jdbc;

import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Map;


/**
 * Converter for char[]->byte[] and byte[]->char[] for single-byte character
 * sets. Much faster (5-6x) than the built-in solution that ships with the
 * JVM, even with JDK-1.4.x and NewIo.
 *
 * @author Mark Matthews
 */
public class SingleByteCharsetConverter {
    // The initial charToByteMap, with all char mappings mapped 
    // to (byte) '?', so that unknown characters are mapped to '?'
    // instead of '\0' (which means end-of-string to MySQL).
    private static byte[] unknownCharsMap = new byte[65536];
    private static final int BYTE_RANGE = (1 + Byte.MAX_VALUE) - Byte.MIN_VALUE;
    private static final Map CONVERTER_MAP = new HashMap();
    private static byte[] allBytes = new byte[BYTE_RANGE];

    static {
        for (int i = Byte.MIN_VALUE; i <= Byte.MAX_VALUE; i++) {
            allBytes[i - Byte.MIN_VALUE] = (byte) i;
        }

        for (int i = 0; i < unknownCharsMap.length; i++) {
            unknownCharsMap[i] = (byte) '?'; // use something 'sane' for unknown chars
        }
    }

    private char[] byteToChars = new char[BYTE_RANGE];
    private byte[] charToByteMap = new byte[65536];

    /**
     * Prevent instantiation, called out of static method initCharset().
     *
     * @param encodingName a JVM character encoding
     *
     * @throws UnsupportedEncodingException if the JVM does not support the
     *         encoding
     */
    private SingleByteCharsetConverter(String encodingName)
        throws UnsupportedEncodingException {
        String allBytesString = new String(allBytes, 0, BYTE_RANGE, encodingName);
        int allBytesLen = allBytesString.length();

        System.arraycopy(unknownCharsMap, 0, charToByteMap, 0,
            charToByteMap.length);

        for (int i = 0; (i < BYTE_RANGE) && (i < allBytesLen); i++) {
            char c = allBytesString.charAt(i);
            byteToChars[i] = c;
            charToByteMap[c] = allBytes[i];
        }
    }

    /**
     * Get a converter for the given encoding name
     *
     * @param encodingName the Java character encoding name
     *
     * @return a converter for the given encoding name
     *
     * @throws UnsupportedEncodingException if the character encoding is not
     *         supported
     */
    public static synchronized SingleByteCharsetConverter getInstance(
        String encodingName) throws UnsupportedEncodingException {
        SingleByteCharsetConverter instance = (SingleByteCharsetConverter) CONVERTER_MAP
            .get(encodingName);

        if (instance == null) {
            instance = initCharset(encodingName);
        }

        return instance;
    }

    /**
     * Initialize the shared instance of a converter for the given character
     * encoding.
     *
     * @param javaEncodingName the Java name for the character set to
     *        initialize
     *
     * @return a converter for the given character set
     *
     * @throws UnsupportedEncodingException if the character encoding is not
     *         supported
     */
    public static SingleByteCharsetConverter initCharset(
        String javaEncodingName) throws UnsupportedEncodingException {
        String mysqlEncodingName = (String) CharsetMapping.JAVA_TO_MYSQL_CHARSET_MAP
            .get(javaEncodingName);

        if (mysqlEncodingName == null) {
            return null;
        }

        if (CharsetMapping.MULTIBYTE_CHARSETS.containsKey(mysqlEncodingName)) {
            return null;
        }

        SingleByteCharsetConverter converter = new SingleByteCharsetConverter(javaEncodingName);

        CONVERTER_MAP.put(javaEncodingName, converter);

        return converter;
    }

    /**
     * Convert the byte buffer from startPos to a length of length to a string
     * using the default platform encoding.
     *
     * @param buffer the bytes to convert
     * @param startPos the index to start at
     * @param length the number of bytes to convert
     *
     * @return the String representation of the given bytes
     */
    public static String toStringDefaultEncoding(byte[] buffer, int startPos,
        int length) {
        return new String(buffer, startPos, length);
    }

    /**
     * Convert the given string to an array of bytes.
     *
     * @param s the String to convert
     *
     * @return the bytes that make up the String
     */
    public final byte[] toBytes(String s) {
        if (s == null) {
            return null;
        }

        int length = s.length();
        byte[] bytes = new byte[length];

        for (int i = 0; i < length; i++) {
            char c = s.charAt(i);
            bytes[i] = charToByteMap[c];
        }

        return bytes;
    }

    private final static byte[] EMPTY_BYTE_ARRAY = new byte[0];
    
    /**
     * Convert the given string to an array of bytes.
     *
     * @param s the String to convert
     * @param offset the offset to start at
     * @param length length (max) to convert
     *
     * @return the bytes that make up the String
     */
    public final byte[] toBytes(String s, int offset, int length) {
        if (s == null) {
            return null;
        }

        if (length == 0) {
        	return EMPTY_BYTE_ARRAY;
        }
        
        int stringLength = s.length();
        byte[] bytes = new byte[length];

       
        for (int i = 0; (i < length); i++) {
            char c = s.charAt(i + offset);
            bytes[i] = charToByteMap[c];
        }

        return bytes;
    }

    /**
     * Convert the byte buffer to a string using this instance's character
     * encoding.
     *
     * @param buffer the bytes to convert to a String
     *
     * @return the converted String
     */
    public final String toString(byte[] buffer) {
        return toString(buffer, 0, buffer.length);
    }

    /**
     * Convert the byte buffer from startPos to a length of length to a string
     * using this instance's character encoding.
     *
     * @param buffer the bytes to convert
     * @param startPos the index to start at
     * @param length the number of bytes to convert
     *
     * @return the String representation of the given bytes
     */
    public final String toString(byte[] buffer, int startPos, int length) {
        char[] charArray = new char[length];
        int readpoint = startPos;

        for (int i = 0; i < length; i++) {
            charArray[i] = byteToChars[(int) buffer[readpoint] - Byte.MIN_VALUE];
            readpoint++;
        }

        return new String(charArray);
    }
}