utf8 unicode java_Java实现的utf8，gbk，unicode编码相互转换的代码

以下是Java实现的UTF-8、GBK、Unicode编码相互转换的代码：

UTF-8转换为Unicode：

public static String utf8ToUnicode(String str) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < str.length(); ) {
        char c = str.charAt(i);
        if ((c & 0x80) == 0) {
            // 单字节字符
            sb.append(c);
            i++;
        } else if ((c & 0xE0) == 0xC0) {
            // 双字节字符
            int codepoint = ((c & 0x1F) << 6) | (str.charAt(i + 1) & 0x3F);
            sb.append((char) codepoint);
            i += 2;
        } else {
            // 三字节字符
            int codepoint = ((c & 0xF) << 12) | ((str.charAt(i + 1) & 0x3F) << 6) | (str.charAt(i + 2) & 0x3F);
            sb.append((char) codepoint);
            i += 3;
        }
    }
    return sb.toString();
}

GBK转换为Unicode：

public static String gbkToUnicode(String str) {
    StringBuilder sb = new StringBuilder();
    try {
        byte[] bytes = str.getBytes("GBK");
        for (int i = 0; i < bytes.length; ) {
            int codepoint = ((bytes[i] & 0xFF) << 8) | (bytes[i + 1] & 0xFF);
            sb.append((char) codepoint);
            i += 2;
        }
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    }
    return sb.toString();
}

Unicode转换为UTF-8：

public static String unicodeToUtf8(String str) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        if (c <= 0x7F) {
            sb.append(c);
        } else if (c <= 0x7FF) {
            sb.append((char) (((c >> 6) & 0x1F) | 0xC0));
            sb.append((char) ((c & 0x3F) | 0x80));
        } else {
            sb.append((char) (((c >> 12) & 0xF) | 0xE0));
            sb.append((char) (((c >> 6) & 0x3F) | 0x80));
            sb.append((char) ((c & 0x3F) | 0x80));
        }
    }
    return sb.toString();
}

Unicode转换为GBK：

public static String unicodeToGbk(String str) {
    StringBuilder sb = new StringBuilder();
    try {
        byte[] bytes = str.getBytes("Unicode");
        for (int i = 2; i < bytes.length; i += 2) {
            int codepoint = ((bytes[i + 1] & 0xFF) << 8) | (bytes[i] & 0xFF);
            byte[] bs = String.valueOf((char) codepoint).getBytes("GBK");
            sb.append(new String(bs, "GBK"));
        }
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    }
    return sb.toString();
}

以上代码仅供参考，实际使用时需要根据具体情况进行调整。