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;
}
}