singlebytecharsetconverter.java

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/*
   Copyright (C) 2002 MySQL AB

      This program is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published by
      the Free Software Foundation; either version 2 of the License, or
      (at your option) any later version.

      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);
    }
}