java中GB2312 To Utf-8字符互换

实现思路大致如下：
取得一个汉字的Unicode码
把Unicode码分解为两个16进制数据字符串（丢弃前两个字节）
把这两个16进制数据字符串转换成二进制数据字符串
把二进制数据字符串分解为三个串，第一个串为4（0~4）个位，在高位加上标记位“1110”，第二（4~10）、三个（10~16）串均为6个位，分别在高位加上“10”标记位
把这三个二进制串分别转换为10进制数据并赋值给字节型数组
根据这个字节型数组构造UTF-8字符
java 代码

import java.io.File;  
import java.io.FileOutputStream;  
import java.io.UnsupportedEncodingException;  
 
/** 
* 2007-8-10 jyin at gomez dot com 
*/ 
public class CharsetConvertor {  
    public static void main(String[] args) {  
        String str = "This is a test for *中网!@#$。，？";  
        try {  
            File f = new File("D:/test.txt");  
            FileOutputStream fio = new FileOutputStream(f);  
            String s = gbToUtf8(str);  
            fio.write(s.getBytes("UTF-8"));  
            fio.close();  
        }  
        catch (Exception e) {  
            e.printStackTrace();  
        }  
    }  
 
    public static String gbToUtf8(String str) throws UnsupportedEncodingException {  
        StringBuffer sb = new StringBuffer();  
        for (int i = 0; i < str.length(); i++) {  
            String s = str.substring(i, i + 1);  
            if (s.charAt(0) > 0x80) {  
                byte[] bytes = s.getBytes("Unicode");  
                String binaryStr = "";  
                for (int j = 2; j < bytes.length; j += 2) {  
                    // the first byte  
                    String hexStr = getHexString(bytes[j + 1]);  
                    String binStr = getBinaryString(Integer.valueOf(hexStr, 16));  
                    binaryStr += binStr;  
                    // the second byte  
                    hexStr = getHexString(bytes[j]);  
                    binStr = getBinaryString(Integer.valueOf(hexStr, 16));  
                    binaryStr += binStr;  
                }  
                // convert unicode to utf-8  
                String s1 = "1110" + binaryStr.substring(0, 4);  
                String s2 = "10" + binaryStr.substring(4, 10);  
                String s3 = "10" + binaryStr.substring(10, 16);  
                byte[] bs = new byte[3];  
                bs[0] = Integer.valueOf(s1, 2).byteValue();  
                bs[1] = Integer.valueOf(s2, 2).byteValue();  
                bs[2] = Integer.valueOf(s3, 2).byteValue();  
                String ss = new String(bs, "UTF-8");  
                sb.append(ss);  
            } else {  
                sb.append(s);  
            }  
        }  
        return sb.toString();  
    }  
 
    private static String getHexString(byte b) {  
        String hexStr = Integer.toHexString(b);  
        int m = hexStr.length();  
        if (m < 2) {  
            hexStr = "0" + hexStr;  
        } else {  
            hexStr = hexStr.substring(m - 2);  
        }  
        return hexStr;  
    }  
 
    private static String getBinaryString(int i) {  
        String binaryStr = Integer.toBinaryString(i);  
        int length = binaryStr.length();  
        for (int l = 0; l < 8 - length; l++) {  
            binaryStr = "0" + binaryStr;  
        }  
        return binaryStr;  
    }  
}