轉載請註明出處！

做專案時候根據協議在傳送網路流的時候需要將所有int及long轉換成byte，因此寫了以下的轉換方法，希望能幫助到需要的朋友 ^_^

閒話少說，直接上碼。

public class Utilities {
	public static byte[] int2Bytes(int num) {
		byte[] byteNum = new byte[4];
		for (int ix = 0; ix < 4; ++ix) {
			int offset = 32 - (ix + 1) * 8;
			byteNum[ix] = (byte) ((num >> offset) & 0xff);
		}
		return byteNum;
	}

	public static int bytes2Int(byte[] byteNum) {
		int num = 0;
		for (int ix = 0; ix < 4; ++ix) {
			num <<= 8;
			num |= (byteNum[ix] & 0xff);
		}
		return num;
	}

	public static byte int2OneByte(int num) {
		return (byte) (num & 0x000000ff);
	}

	public static int oneByte2Int(byte byteNum) {
 

                //針對正數的int
		return byteNum > 0 ? byteNum : (128 + (128 + byteNum));
	}

	public static byte[] long2Bytes(long num) {
		byte[] byteNum = new byte[8];
		for (int ix = 0; ix < 8; ++ix) {
			int offset = 64 - (ix + 1) * 8;
			byteNum[ix] = (byte) ((num >> offset) & 0xff);
		}
		return byteNum;
	}

	public static long bytes2Long(byte[] byteNum) {
		long num = 0;
		for (int ix = 0; ix < 8; ++ix) {
			num <<= 8;
			num |= (byteNum[ix] & 0xff);
		}
		return num;
	}
}
 

public class TestMain {
	public static void main(String[] args) {
		int num = 129;
		System.out.println("測試的int值為:" + num);

		byte[] int2bytes = Utilities.int2Bytes(num);
		System.out.printf("int轉成bytes: ");
		for (int i = 0; i < 4; ++i) {
			System.out.print(int2bytes[i] + " ");
		}
		System.out.println();

		int bytes2int = Utilities.bytes2Int(int2bytes);
		System.out.println("bytes轉行成int: " + bytes2int);

		byte int2OneByte = Utilities.int2OneByte(num);
		System.out.println("int轉行成one byte: " + int2OneByte);

		int oneByte2Int = Utilities.oneByte2Int(int2OneByte);
		System.out.println("one byte轉行成int: " + oneByte2Int);
		System.out.println();

		long longNum = 100000;
		System.out.println("測試的long值為：" + longNum);

		byte[] long2Bytes = Utilities.long2Bytes(longNum);
		System.out.printf("long轉行成bytes: ");
		for (int ix = 0; ix < long2Bytes.length; ++ix) {
			System.out.print(long2Bytes[ix] + " ");
		}
		System.out.println();

		long bytes2Long = Utilities.bytes2Long(long2Bytes);
		System.out.println("bytes轉行成long: " + bytes2Long);
	}
}
 

測試的int值為:156
int轉成bytes: 0 0 0 -100 
bytes轉行成int: 156
int轉行成one byte: -100
one byte轉行成int: 156

測試的long值為：100000
long轉行成bytes: 0 0 0 0 0 1 -122 -96 
bytes轉行成long: 100000