Native2Ascii和Ascii2Native的Java实现

下午同事说要一个Native2Ascii和Ascii2Native的Java实现，Google了半天发现有的是错误的实现，有的只有Native2Ascii没有Ascii2Native，有的又是其他语言实现的，干脆自己参考着写了一个。 

package util;

/**
 * native2ascii.exe Java code implementation.
 *
 * @author
 * @version 1.0
 */
public class Native2AsciiUtils {

    /**
     * prefix of ascii string of native character
     */
    private static String PREFIX = "\\u";

    /**
     * Native to ascii string. It's same as execut native2ascii.exe.
     *
     * @param str
     *            native string
     * @return ascii string
     */
    public static String native2Ascii(String str) {
        char[] chars = str.toCharArray();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < chars.length; i++) {
            sb.append(char2Ascii(chars[i]));
        }
        return sb.toString();
    }

    /**
     * Native character to ascii string.
     *
     * @param c
     *            native character
     * @return ascii string
     */
    private static String char2Ascii(char c) {
        if (c > 255) {
            StringBuilder sb = new StringBuilder();
            sb.append(PREFIX);
            int code = (c >> 8);
            String tmp = Integer.toHexString(code);
            if (tmp.length() == 1) {
                sb.append("0");
            }
            sb.append(tmp);
            code = (c & 0xFF);
            tmp = Integer.toHexString(code);
            if (tmp.length() == 1) {
                sb.append("0");
            }
            sb.append(tmp);
            return sb.toString();
        } else {
            return Character.toString(c);
        }
    }

    /**
     * Ascii to native string. It's same as execut native2ascii.exe -reverse.
     *
     * @param str
     *            ascii string
     * @return native string
     */
    public static String ascii2Native(String str) {
        StringBuilder sb = new StringBuilder();
        int begin = 0;
        int index = str.indexOf(PREFIX);
        while (index != -1) {
            sb.append(str.substring(begin, index));
            sb.append(ascii2Char(str.substring(index, index + 6)));
            begin = index + 6;
            index = str.indexOf(PREFIX, begin);
        }
        sb.append(str.substring(begin));
        return sb.toString();
    }

    /**
     * Ascii to native character.
     *
     * @param str
     *            ascii string
     * @return native character
     */
    private static char ascii2Char(String str) {
        if (str.length() != 6) {
            throw new IllegalArgumentException(
                    "Ascii string of a native character must be 6 character.");
        }
        if (!PREFIX.equals(str.substring(0, 2))) {
            throw new IllegalArgumentException(
                    "Ascii string of a native character must start with \"\\u\".");
        }
        String tmp = str.substring(2, 4);
        int code = Integer.parseInt(tmp, 16) << 8;
        tmp = str.substring(4, 6);
        code += Integer.parseInt(tmp, 16);
        return (char) code;
    }

}