Java：转换汉字为unicode形式的字符串和转换unicode形式字符串转换成汉字

/* 输出
Original:       黄   彪彪
to unicode:     \u9EC4\ \t\u5F6A\u5F6A
from unicode:   黄   彪彪
使用命令转换: native2ascii -encoding utf-8 a.txt a.txt
Java的properties属性文件会把字符先转换成unicode的形式存储.
*/

import java.io.UnsupportedEncodingException;

public class UnicodeConverter {
    public static void main(String[] args) throws UnsupportedEncodingException {
        String s = "黄 \t彪\u5F6A";
        System.out.println("Original:\t\t" + s);

        s = toEncodedUnicode(s, true);
        System.out.println("to unicode:\t\t" + s);

        s = fromEncodedUnicode(s.toCharArray(), 0, s.length());
        System.out.println("from unicode:\t" + s);
    }

    private static final char[] hexDigit = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A',
            'B', 'C', 'D', 'E', 'F' };

    private static char toHex(int nibble) {
        return hexDigit[(nibble & 0xF)];
    }

    /**
     * 将字符串编码成 Unicode 形式的字符串. 如 "黄" to "\u9EC4"
     * Converts unicodes to encoded \\uxxxx and escapes
     * special characters with a preceding slash
     * 
     * @param theString
     *        待转换成Unicode编码的字符串。
     * @param escapeSpace
     *        是否忽略空格，为true时在空格后面是否加个反斜杠。
     * @return 返回转换后Unicode编码的字符串。
     */
    public static String toEncodedUnicode(String theString, boolean escapeSpace) {
        int len = theString.length();
        int bufLen = len * 2;
        if (bufLen < 0) {
            bufLen = Integer.MAX_VALUE;
        }
        StringBuffer outBuffer = new StringBuffer(bufLen);

        for (int x = 0; x < len; x++) {
            char aChar = theString.charAt(x);
            // Handle common case first, selecting largest block that
            // avoids the specials below
            if ((aChar > 61) && (aChar < 127)) {
                if (aChar == '\\') {
                    outBuffer.append('\\');
                    outBuffer.append('\\');
                    continue;
                }
                outBuffer.append(aChar);
                continue;
            }
            
            switch (aChar) {
            case ' ':
                if (x == 0 || escapeSpace) outBuffer.append('\\');
                outBuffer.append(' ');
                break;
            case '\t':
                outBuffer.append('\\');
                outBuffer.append('t');
                break;
            case '\n':
                outBuffer.append('\\');
                outBuffer.append('n');
                break;
            case '\r':
                outBuffer.append('\\');
                outBuffer.append('r');
                break;
            case '\f':
                outBuffer.append('\\');
                outBuffer.append('f');
                break;
            case '=': // Fall through
            case ':': // Fall through
            case '#': // Fall through
            case '!':
                outBuffer.append('\\');
                outBuffer.append(aChar);
                break;
            default:
                if ((aChar < 0x0020) || (aChar > 0x007e)) {
                    // 每个unicode有16位，每四位对应的16进制从高位保存到低位
                    outBuffer.append('\\');
                    outBuffer.append('u');
                    outBuffer.append(toHex((aChar >> 12) & 0xF));
                    outBuffer.append(toHex((aChar >> 8) & 0xF));
                    outBuffer.append(toHex((aChar >> 4) & 0xF));
                    outBuffer.append(toHex(aChar & 0xF));
                } else {
                    outBuffer.append(aChar);
                }
            }
        }
        return outBuffer.toString();
    }

    /**
     * 从 Unicode 形式的字符串转换成对应的编码的特殊字符串。 如 "\u9EC4" to "黄".
     * Converts encoded \\uxxxx to unicode chars
     * and changes special saved chars to their original forms
     * 
     * @param in
     *        Unicode编码的字符数组。
     * @param off
     *        转换的起始偏移量。
     * @param len
     *        转换的字符长度。
     * @param convtBuf
     *        转换的缓存字符数组。
     * @return 完成转换，返回编码前的特殊字符串。
     */
    public static String fromEncodedUnicode(char[] in, int off, int len) {
        char aChar;
        char[] out = new char[len]; // 只短不长
        int outLen = 0;
        int end = off + len;

        while (off < end) {
            aChar = in[off++];
            if (aChar == '\\') {
                aChar = in[off++];
                if (aChar == 'u') {
                    // Read the xxxx
                    int value = 0;
                    for (int i = 0; i < 4; i++) {
                        aChar = in[off++];
                        switch (aChar) {
                        case '0':
                        case '1':
                        case '2':
                        case '3':
                        case '4':
                        case '5':
                        case '6':
                        case '7':
                        case '8':
                        case '9':
                            value = (value << 4) + aChar - '0';
                            break;
                        case 'a':
                        case 'b':
                        case 'c':
                        case 'd':
                        case 'e':
                        case 'f':
                            value = (value << 4) + 10 + aChar - 'a';
                            break;
                        case 'A':
                        case 'B':
                        case 'C':
                        case 'D':
                        case 'E':
                        case 'F':
                            value = (value << 4) + 10 + aChar - 'A';
                            break;
                        default:
                            throw new IllegalArgumentException("Malformed \\uxxxx encoding.");
                        }
                    }
                    out[outLen++] = (char) value;
                } else {
                    if (aChar == 't') {
                        aChar = '\t';
                    } else if (aChar == 'r') {
                        aChar = '\r';
                    } else if (aChar == 'n') {
                        aChar = '\n';
                    } else if (aChar == 'f') {
                        aChar = '\f';
                    }
                    out[outLen++] = aChar;
                }
            } else {
                out[outLen++] = (char) aChar;
            }
        }
        return new String(out, 0, outLen);
    }
}