java中byte數組與int，long，short間的轉換

package com.util;

/**
 * 
 * <ul>
 * <li>文件名稱: com.born.util.ByteUtil.java</li>
 * <li>文件描述: byte轉換工具</li>
 * <li>版權所有: 版權所有(C)2001-2006</li>
 * <li>公 司: bran</li>
 * <li>內容摘要:</li>
 * <li>其他說明:</li>
 * <li>完成日期：2011-7-18</li>
 * <li>修改記錄0：無</li>
 * </ul>
 * 
 * @version 1.0
 * @author 許力多
 */
public class ByteUtil {
	/**
	 * 轉換short爲byte
	 * 
	 * @param b
	 * @param s
	 *            需要轉換的short
	 * @param index
	 */
	public static void putShort(byte b[], short s, int index) {
		b[index + 1] = (byte) (s >> 8);
		b[index + 0] = (byte) (s >> 0);
	}

	/**
	 * 通過byte數組取到short
	 * 
	 * @param b
	 * @param index
	 *            第幾位開始取
	 * @return
	 */
	public static short getShort(byte[] b, int index) {
		return (short) (((b[index + 1] << 8) | b[index + 0] & 0xff));
	}

	/**
	 * 轉換int爲byte數組
	 * 
	 * @param bb
	 * @param x
	 * @param index
	 */
	public static void putInt(byte[] bb, int x, int index) {
		bb[index + 3] = (byte) (x >> 24);
		bb[index + 2] = (byte) (x >> 16);
		bb[index + 1] = (byte) (x >> 8);
		bb[index + 0] = (byte) (x >> 0);
	}

	/**
	 * 通過byte數組取到int
	 * 
	 * @param bb
	 * @param index
	 *            第幾位開始
	 * @return
	 */
	public static int getInt(byte[] bb, int index) {
		return (int) ((((bb[index + 3] & 0xff) << 24)
				| ((bb[index + 2] & 0xff) << 16)
				| ((bb[index + 1] & 0xff) << 8) | ((bb[index + 0] & 0xff) << 0)));
	}

	/**
	 * 轉換long型爲byte數組
	 * 
	 * @param bb
	 * @param x
	 * @param index
	 */
	public static void putLong(byte[] bb, long x, int index) {
		bb[index + 7] = (byte) (x >> 56);
		bb[index + 6] = (byte) (x >> 48);
		bb[index + 5] = (byte) (x >> 40);
		bb[index + 4] = (byte) (x >> 32);
		bb[index + 3] = (byte) (x >> 24);
		bb[index + 2] = (byte) (x >> 16);
		bb[index + 1] = (byte) (x >> 8);
		bb[index + 0] = (byte) (x >> 0);
	}

	/**
	 * 通過byte數組取到long
	 * 
	 * @param bb
	 * @param index
	 * @return
	 */
	public static long getLong(byte[] bb, int index) {
		return ((((long) bb[index + 7] & 0xff) << 56)
				| (((long) bb[index + 6] & 0xff) << 48)
				| (((long) bb[index + 5] & 0xff) << 40)
				| (((long) bb[index + 4] & 0xff) << 32)
				| (((long) bb[index + 3] & 0xff) << 24)
				| (((long) bb[index + 2] & 0xff) << 16)
				| (((long) bb[index + 1] & 0xff) << 8) | (((long) bb[index + 0] & 0xff) << 0));
	}

	/**
	 * 字符到字節轉換
	 * 
	 * @param ch
	 * @return
	 */
	public static void putChar(byte[] bb, char ch, int index) {
		int temp = (int) ch;
		// byte[] b = new byte[2];
		for (int i = 0; i < 2; i ++ ) {
			bb[index + i] = new Integer(temp & 0xff).byteValue(); // 將最高位保存在最低位
			temp = temp >> 8; // 向右移8位
		}
	}

	/**
	 * 字節到字符轉換
	 * 
	 * @param b
	 * @return
	 */
	public static char getChar(byte[] b, int index) {
		int s = 0;
		if (b[index + 1] > 0)
			s += b[index + 1];
		else
			s += 256 + b[index + 0];
		s *= 256;
		if (b[index + 0] > 0)
			s += b[index + 1];
		else
			s += 256 + b[index + 0];
		char ch = (char) s;
		return ch;
	}

	/**
	 * float轉換byte
	 * 
	 * @param bb
	 * @param x
	 * @param index
	 */
	public static void putFloat(byte[] bb, float x, int index) {
		// byte[] b = new byte[4];
		int l = Float.floatToIntBits(x);
		for (int i = 0; i < 4; i++) {
			bb[index + i] = new Integer(l).byteValue();
			l = l >> 8;
		}
	}

	/**
	 * 通過byte數組取得float
	 * 
	 * @param bb
	 * @param index
	 * @return
	 */
	public static float getFloat(byte[] b, int index) {
		int l;
		l = b[index + 0];
		l &= 0xff;
		l |= ((long) b[index + 1] << 8);
		l &= 0xffff;
		l |= ((long) b[index + 2] << 16);
		l &= 0xffffff;
		l |= ((long) b[index + 3] << 24);
		return Float.intBitsToFloat(l);
	}

	/**
	 * double轉換byte
	 * 
	 * @param bb
	 * @param x
	 * @param index
	 */
	public static void putDouble(byte[] bb, double x, int index) {
		// byte[] b = new byte[8];
		long l = Double.doubleToLongBits(x);
		for (int i = 0; i < 4; i++) {
			bb[index + i] = new Long(l).byteValue();
			l = l >> 8;
		}
	}

	/**
	 * 通過byte數組取得float
	 * 
	 * @param bb
	 * @param index
	 * @return
	 */
	public static double getDouble(byte[] b, int index) {
		long l;
		l = b[0];
		l &= 0xff;
		l |= ((long) b[1] << 8);
		l &= 0xffff;
		l |= ((long) b[2] << 16);
		l &= 0xffffff;
		l |= ((long) b[3] << 24);
		l &= 0xffffffffl;
		l |= ((long) b[4] << 32);
		l &= 0xffffffffffl;
		l |= ((long) b[5] << 40);
		l &= 0xffffffffffffl;
		l |= ((long) b[6] << 48);
		l &= 0xffffffffffffffl;
		l |= ((long) b[7] << 56);
		return Double.longBitsToDouble(l);
	}
}

public class DataTypeChangeHelper {
	/**
	 * 將一個單字節的byte轉換成32位的int
	 * 
	 * @param b
	 *            byte
	 * @return convert result
	 */
	public static int unsignedByteToInt(byte b) {
		return (int) b & 0xFF;
	}

	/**
	 * 將一個單字節的Byte轉換成十六進制的數
	 * 
	 * @param b
	 *            byte
	 * @return convert result
	 */
	public static String byteToHex(byte b) {
		int i = b & 0xFF;
		return Integer.toHexString(i);
	}

	/**
	 * 將一個4byte的數組轉換成32位的int
	 * 
	 * @param buf
	 *            bytes buffer
	 * @param byte[]中開始轉換的位置
	 * @return convert result
	 */
	public static long unsigned4BytesToInt(byte[] buf, int pos) {
		int firstByte = 0;
		int secondByte = 0;
		int thirdByte = 0;
		int fourthByte = 0;
		int index = pos;
		firstByte = (0x000000FF & ((int) buf[index]));
		secondByte = (0x000000FF & ((int) buf[index + 1]));
		thirdByte = (0x000000FF & ((int) buf[index + 2]));
		fourthByte = (0x000000FF & ((int) buf[index + 3]));
		index = index + 4;
		return ((long) (firstByte << 24 | secondByte << 16 | thirdByte << 8 | fourthByte)) & 0xFFFFFFFFL;
	}

	/**
	 * 將16位的short轉換成byte數組
	 * 
	 * @param s
	 *            short
	 * @return byte[] 長度爲2
	 * */
	public static byte[] shortToByteArray(short s) {
		byte[] targets = new byte[2];
		for (int i = 0; i < 2; i++) {
			int offset = (targets.length - 1 - i) * 8;
			targets[i] = (byte) ((s >>> offset) & 0xff);
		}
		return targets;
	}

	/**
	 * 將32位整數轉換成長度爲4的byte數組
	 * 
	 * @param s
	 *            int
	 * @return byte[]
	 * */
	public static byte[] intToByteArray(int s) {
		byte[] targets = new byte[2];
		for (int i = 0; i < 4; i++) {
			int offset = (targets.length - 1 - i) * 8;
			targets[i] = (byte) ((s >>> offset) & 0xff);
		}
		return targets;
	}

	/**
	 * long to byte[]
	 * 
	 * @param s
	 *            long
	 * @return byte[]
	 * */
	public static byte[] longToByteArray(long s) {
		byte[] targets = new byte[2];
		for (int i = 0; i < 8; i++) {
			int offset = (targets.length - 1 - i) * 8;
			targets[i] = (byte) ((s >>> offset) & 0xff);
		}
		return targets;
	}

	/**32位int轉byte[]*/
	public static byte[] int2byte(int res) {
		byte[] targets = new byte[4];
		targets[0] = (byte) (res & 0xff);// 最低位
		targets[1] = (byte) ((res >> 8) & 0xff);// 次低位
		targets[2] = (byte) ((res >> 16) & 0xff);// 次高位
		targets[3] = (byte) (res >>> 24);// 最高位,無符號右移。
		return targets;
	}

	/**
	 * 將長度爲2的byte數組轉換爲16位int
	 * 
	 * @param res
	 *            byte[]
	 * @return int
	 * */
	public static int byte2int(byte[] res) {
		// res = InversionByte(res);
		// 一個byte數據左移24位變成0x??000000，再右移8位變成0x00??0000
		int targets = (res[0] & 0xff) | ((res[1] << 8) & 0xff00); // | 表示安位或
		return targets;
	}
}

原文：http://blog.csdn.net/leetcworks/article/details/7390731