Java 十六進制與字串雙向轉換完整工具類（含 UTF-8、Byte 陣列、印表格式化）

核心需求

• 字串 → 十六進制（Hex）
• 十六進制 → 字串
• 支援中文等多位元組字元（UTF-8）
• Byte 陣列格式化輸出（如 0x2B 0x44）

方案一：標準庫 Integer.toHexString + 手動補零

public class HexUtils {
    // 字串 → Hex (UTF-8)
    public static String encode(String str) {
        byte[] bytes = str.getBytes(StandardCharsets.UTF_8);
        StringBuilder sb = new StringBuilder(bytes.length * 2);
        for (byte b : bytes) {
            sb.append(String.format("%02X", b)); // 大寫、兩位、不足補零
        }
        return sb.toString();
    }

    // Hex → 字串 (UTF-8)
    public static String decode(String hex) {
        int len = hex.length();
        byte[] bytes = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            bytes[i / 2] = (byte) Integer.parseInt(hex.substring(i, i + 2), 16);
        }
        return new String(bytes, StandardCharsets.UTF_8);
    }

    // Byte[] → 格式化 Hex 字串（含空格、大寫）
    public static String bytesToHexString(byte[] bytes) {
        StringBuilder sb = new StringBuilder(bytes.length * 3);
        for (byte b : bytes) {
            sb.append(String.format("%02X ", b));
        }
        return sb.toString().trim();
    }

    // Hex 字串 → Byte[]（每兩字元一 byte）
    public static byte[] hexStringToBytes(String hex) {
        hex = hex.replaceAll("\\s+", ""); // 移除空格
        byte[] bytes = new byte[hex.length() / 2];
        for (int i = 0; i < bytes.length; i++) {
            bytes[i] = (byte) Integer.parseInt(hex.substring(i * 2, i * 2 + 2), 16);
        }
        return bytes;
    }
}

方案二：查表法（效能更高、無格式化開銷）

public class HexUtilsFast {
    private static final char[] HEX = "0123456789ABCDEF".toCharArray();

    public static String encode(byte[] bytes) {
        char[] chars = new char[bytes.length * 2];
        for (int i = 0, j = 0; i < bytes.length; i++) {
            chars[j++] = HEX[(bytes[i] & 0xF0) >>> 4];
            chars[j++] = HEX[bytes[i] & 0x0F];
        }
        return new String(chars);
    }

    public static byte[] decode(String hex) {
        hex = hex.replaceAll("\\s+", "");
        byte[] bytes = new byte[hex.length() / 2];
        for (int i = 0; i < bytes.length; i++) {
            int high = Character.digit(hex.charAt(i * 2), 16);
            int low  = Character.digit(hex.charAt(i * 2 + 1), 16);
            bytes[i] = (byte) ((high << 4) | low);
        }
        return bytes;
    }
}

方案三：Apache Commons Codec / Spring / Guava 一行搞定

// Commons Codec
String hex = Hex.encodeHexString(bytes);
byte[] bytes = Hex.decodeHex(hex.toCharArray());

// Spring Framework
String hex = org.springframework.util.StringUtils.bytesToHexString(bytes);
// 注：Spring 5.3+ 提供 HexFormat (Java 17+)

// Java 17+ 標準庫
String hex = java.util.HexFormat.of().formatHex(bytes);
byte[] bytes = java.util.HexFormat.of().parseHex(hex);

實戰：列印 Byte 陣列供除錯

public static void printHex(String hint, byte[] data) {
    System.out.print(hint + ": ");
    for (byte b : data) {
        System.out.printf("%02X ", b);
    }
    System.out.println();
}
// 輸出範例：CMD: 2B 44 EF D9

測試驗證

public static void main(String[] args) {
    String original = "中文測試123";
    String hex = HexUtils.encode(original);
    String decoded = HexUtils.decode(hex);
    System.out.println("原文：" + original);
    System.out.println("Hex：" + hex);
    System.out.println("解碼：" + decoded);
    System.out.println("驗證：" + original.equals(decoded)); // true
}

總結建議