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Java byte 陣列與基本類型互轉工具類：int、long、short、float、double、char 完整實作

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Java byte 陣列與基本類型互轉工具類

網路傳輸、序列化、二進制協議解析常需在 byte[] 與基本類型間轉換。本文提供完整、可直接使用的工具類，涵蓋有號/無號、大端/小端場景。

一、核心轉換邏輯（大端序 Big-Endian）

public class ByteUtil {

    // short (2 bytes)
    public static void putShort(byte[] b, short s, int index) {
        b[index + 1] = (byte)(s >> 8);
        b[index + 0] = (byte)(s >> 0);
    }
    public static short getShort(byte[] b, int index) {
        return (short)(((b[index + 1] << 8) | (b[index + 0] & 0xFF)));
    }

    // int (4 bytes)
    public static void putInt(byte[] b, int x, int index) {
        b[index + 3] = (byte)(x >> 24);
        b[index + 2] = (byte)(x >> 16);
        b[index + 1] = (byte)(x >> 8);
        b[index + 0] = (byte)(x >> 0);
    }
    public static int getInt(byte[] b, int index) {
        return ((b[index + 3] & 0xFF) << 24) |
               ((b[index + 2] & 0xFF) << 16) |
               ((b[index + 1] & 0xFF) << 8)  |
               ((b[index + 0] & 0xFF) << 0);
    }

    // long (8 bytes)
    public static void putLong(byte[] b, long x, int index) {
        b[index + 7] = (byte)(x >> 56);
        b[index + 6] = (byte)(x >> 48);
        b[index + 5] = (byte)(x >> 40);
        b[index + 4] = (byte)(x >> 32);
        b[index + 3] = (byte)(x >> 24);
        b[index + 2] = (byte)(x >> 16);
        b[index + 1] = (byte)(x >> 8);
        b[index + 0] = (byte)(x >> 0);
    }
    public static long getLong(byte[] b, int index) {
        return (((long)b[index + 7] & 0xFF) << 56) |
               (((long)b[index + 6] & 0xFF) << 48) |
               (((long)b[index + 5] & 0xFF) << 40) |
               (((long)b[index + 4] & 0xFF) << 32) |
               (((long)b[index + 3] & 0xFF) << 24) |
               (((long)b[index + 2] & 0xFF) << 16) |
               (((long)b[index + 1] & 0xFF) << 8)  |
               (((long)b[index + 0] & 0xFF) << 0);
    }

    // float (4 bytes) - 透過 intBits 轉換
    public static void putFloat(byte[] b, float x, int index) {
        int bits = Float.floatToIntBits(x);
        putInt(b, bits, index);
    }
    public static float getFloat(byte[] b, int index) {
        int bits = getInt(b, index);
        return Float.intBitsToFloat(bits);
    }

    // double (8 bytes) - 透過 longBits 轉換
    public static void putDouble(byte[] b, double x, int index) {
        long bits = Double.doubleToLongBits(x);
        putLong(b, bits, index);
    }
    public static double getDouble(byte[] b, int index) {
        long bits = getLong(b, index);
        return Double.longBitsToDouble(bits);
    }
}

二、輔助工具方法

public class DataTypeChangeHelper {

    // 無號 byte 轉 int (0-255)
    public static int unsignedByteToInt(byte b) {
        return b & 0xFF;
    }

    // byte 轉十六進制字串
    public static String byteToHex(byte b) {
        return Integer.toHexString(b & 0xFF);
    }

    // 4 bytes 無號轉 long
    public static long unsigned4BytesToInt(byte[] buf, int pos) {
        return ((buf[pos] & 0xFFL) << 24) |
               ((buf[pos+1] & 0xFFL) << 16) |
               ((buf[pos+2] & 0xFFL) << 8)  |
               ((buf[pos+3] & 0xFFL));
    }

    // 基本類型 → byte[] (大端)
    public static byte[] shortToBytes(short s) {
        return new byte[]{(byte)(s >> 8), (byte)(s >> 0)};
    }
    public static byte[] intToBytes(int i) {
        return new byte[]{(byte)(i >> 24), (byte)(i >> 16), (byte)(i >> 8), (byte)(i >> 0)};
    }
    public static byte[] longToBytes(long l) {
        return new byte[]{
            (byte)(l >> 56), (byte)(l >> 48), (byte)(l >> 40), (byte)(l >> 32),
            (byte)(l >> 24), (byte)(l >> 16), (byte)(l >> 8), (byte)(l >> 0)
        };
    }

    // byte[] → 基本類型 (大端)
    public static short bytesToShort(byte[] b) {
        return (short)(((b[0] & 0xFF) << 8) | (b[1] & 0xFF));
    }
    public static int bytesToInt(byte[] b) {
        return ((b[0] & 0xFF) << 24) | ((b[1] & 0xFF) << 16) | ((b[2] & 0xFF) << 8) | (b[3] & 0xFF);
    }
    public static long bytesToLong(byte[] b) {
        return ((long)b[0] & 0xFFL) << 56 | ((long)b[1] & 0xFFL) << 48 |
               ((long)b[2] & 0xFFL) << 40 | ((long)b[3] & 0xFFL) << 32 |
               ((long)b[4] & 0xFFL) << 24 | ((long)b[5] & 0xFFL) << 16 |
               ((long)b[6] & 0xFFL) << 8  | ((long)b[7] & 0xFFL);
    }
}