【转】java中float与byte[]的互转 -- 不错

原文网址：http://tjmljw.iteye.com/blog/1767716

起因：想把一个float[]转换成内存数据，查了一下，下面两个方法可以将float转成byte[]。 

方法一 

import java.nio.ByteBuffer;
import java.util.ArrayList;

float buffer = 0f;
ByteBuffer bbuf = ByteBuffer.allocate(4);
bbuf.putFloat(buffer);
byte[] bBuffer = bbuf.array();
bBuffer=this.dataValueRollback(bBuffer);

       //数值反传
private byte[] dataValueRollback(byte[] data) {
    ArrayList<Byte> al = new ArrayList<Byte>();
    for (int i = data.length - 1; i >= 0; i--) {
        al.add(data[i]);
    }

    byte[] buffer = new byte[al.size()];
    for (int i = 0; i <= buffer.length - 1; i++) {
        buffer[i] = al.get(i);
    }
    return buffer;
}

方法二 
先用 Float.floatToIntBits(f)转换成int 
再通过如下方法转成byte [] 

/**
 * 将int类型的数据转换为byte数组 原理：将int数据中的四个byte取出，分别存储
 *
 * @param n  int数据
 * @return 生成的byte数组
 */
public static byte[] intToBytes2(int n) {
    byte[] b = new byte[4];
    for (int i = 0; i < 4; i++) {
        b[i] = (byte) (n >> (24 - i * 8));
    }
    return b;
}

/**
 * 将byte数组转换为int数据
 *
 * @param b 字节数组
 * @return 生成的int数据
 */
public static int byteToInt2(byte[] b) {
    return (((int) b[0]) << 24) + (((int) b[1]) << 16)
            + (((int) b[2]) << 8) + b[3];
}

方法三（这个是我在用的）： 

/**
 * 浮点转换为字节
 *
 * @param f
 * @return
 */
public static byte[] float2byte(float f) {

    // 把float转换为byte[]
    int fbit = Float.floatToIntBits(f);

    byte[] b = new byte[4];
    for (int i = 0; i < 4; i++) {
        b[i] = (byte) (fbit >> (24 - i * 8));
    }

    // 翻转数组
    int len = b.length;
    // 建立一个与源数组元素类型相同的数组
    byte[] dest = new byte[len];
    // 为了防止修改源数组，将源数组拷贝一份副本
    System.arraycopy(b, 0, dest, 0, len);
    byte temp;
    // 将顺位第i个与倒数第i个交换
    for (int i = 0; i < len / 2; ++i) {
        temp = dest[i];
        dest[i] = dest[len - i - 1];
        dest[len - i - 1] = temp;
    }

    return dest;

}

/**
 * 字节转换为浮点
 *
 * @param b 字节（至少4个字节）
 * @param index 开始位置
 * @return
 */
public static float byte2float(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);
}

2013-05-06 add 
title Java基本类型与byte数组之间相互转换 
from http://blog.sina.com.cn/s/blog_7a35101201012n0b.html 

package com.my.wxf4j.utils;

import java.nio.charset.Charset;

public class ByteUtil
{
    public static byte[] getBytes(short data)
    {
        byte[] bytes = new byte[2];
        bytes[0] = (byte) (data & 0xff);
        bytes[1] = (byte) ((data & 0xff00) >> 8);
        return bytes;
    }

    public static byte[] getBytes(char data)
    {
        byte[] bytes = new byte[2];
        bytes[0] = (byte) (data);
        bytes[1] = (byte) (data >> 8);
        return bytes;
    }

    public static byte[] getBytes(int data)
    {
        byte[] bytes = new byte[4];
        bytes[0] = (byte) (data & 0xff);
        bytes[1] = (byte) ((data & 0xff00) >> 8);
        bytes[2] = (byte) ((data & 0xff0000) >> 16);
        bytes[3] = (byte) ((data & 0xff000000) >> 24);
        return bytes;
    }

    public static byte[] getBytes(long data)
    {
        byte[] bytes = new byte[8];
        bytes[0] = (byte) (data & 0xff);
        bytes[1] = (byte) ((data >> 8) & 0xff);
        bytes[2] = (byte) ((data >> 16) & 0xff);
        bytes[3] = (byte) ((data >> 24) & 0xff);
        bytes[4] = (byte) ((data >> 32) & 0xff);
        bytes[5] = (byte) ((data >> 40) & 0xff);
        bytes[6] = (byte) ((data >> 48) & 0xff);
        bytes[7] = (byte) ((data >> 56) & 0xff);
        return bytes;
    }

    public static byte[] getBytes(float data)
    {
        int intBits = Float.floatToIntBits(data);
        return getBytes(intBits);
    }

    public static byte[] getBytes(double data)
    {
        long intBits = Double.doubleToLongBits(data);
        return getBytes(intBits);
    }

    public static byte[] getBytes(String data, String charsetName)
    {
        Charset charset = Charset.forName(charsetName);
        return data.getBytes(charset);
    }

    public static byte[] getBytes(String data)
    {
        return getBytes(data, "GBK");
    }


    public static short getShort(byte[] bytes)
    {
        return (short) ((0xff & bytes[0]) | (0xff00 & (bytes[1] << 8)));
    }

    public static char getChar(byte[] bytes)
    {
        return (char) ((0xff & bytes[0]) | (0xff00 & (bytes[1] << 8)));
    }

    public static int getInt(byte[] bytes)
    {
        return (0xff & bytes[0]) | (0xff00 & (bytes[1] << 8)) | (0xff0000 & (bytes[2] << 16)) | (0xff000000 & (bytes[3] << 24));
    }

    public static long getLong(byte[] bytes)
    {
        return(0xffL & (long)bytes[0]) | (0xff00L & ((long)bytes[1] << 8)) | (0xff0000L & ((long)bytes[2] << 16)) | (0xff000000L & ((long)bytes[3] << 24))
         | (0xff00000000L & ((long)bytes[4] << 32)) | (0xff0000000000L & ((long)bytes[5] << 40)) | (0xff000000000000L & ((long)bytes[6] << 48)) | (0xff00000000000000L & ((long)bytes[7] << 56));
    }

    public static float getFloat(byte[] bytes)
    {
        return Float.intBitsToFloat(getInt(bytes));
    }

    public static double getDouble(byte[] bytes)
    {
        long l = getLong(bytes);
        System.out.println(l);
        return Double.longBitsToDouble(l);
    }

    public static String getString(byte[] bytes, String charsetName)
    {
        return new String(bytes, Charset.forName(charsetName));
    }

    public static String getString(byte[] bytes)
    {
        return getString(bytes, "GBK");
    }


    public static void main(String[] args)
    {
        short s = 122;
        int i = 122;
        long l = 1222222;

        char c = 'a';

        float f = 122.22f;
        double d = 122.22;

        String string = "我是好孩子";
        System.out.println(s);
        System.out.println(i);
        System.out.println(l);
        System.out.println(c);
        System.out.println(f);
        System.out.println(d);
        System.out.println(string);

        System.out.println("**************");

        System.out.println(getShort(getBytes(s)));
        System.out.println(getInt(getBytes(i)));
        System.out.println(getLong(getBytes(l)));
        System.out.println(getChar(getBytes(c)));
        System.out.println(getFloat(getBytes(f)));
        System.out.println(getDouble(getBytes(d)));
        System.out.println(getString(getBytes(string)));
    }
}