java:bytes[]转long的三种方式

    /**
     * 将字节数组转为long<br>
     * 如果input为null,或offset指定的剩余数组长度不足8字节则抛出异常
     * @param input 
     * @param offset 起始偏移量
     * @param littleEndian 输入数组是否小端模式
     * @return
     */
    public static long longFrom8Bytes(byte[] input, int offset, boolean littleEndian){
        long value=0;
        // 循环读取每个字节通过移位运算完成long的8个字节拼装
        for(int  count=0;count<8;++count){
            int shift=(littleEndian?count:(7-count))<<3;
            value |=((long)0xff<< shift) & ((long)input[offset+count] << shift);
        }
        return value;
    }

    /**
     * 利用 {@link java.nio.ByteBuffer}实现byte[]转long
     * @param input
     * @param offset 
     * @param littleEndian 输入数组是否小端模式
     * @return
     */
    public static long bytesToLong(byte[] input, int offset, boolean littleEndian) { 
        // 将byte[] 封装为 ByteBuffer 
        ByteBuffer buffer = ByteBuffer.wrap(input,offset,8);
        if(littleEndian){
            // ByteBuffer.order(ByteOrder) 方法指定字节序,即大小端模式(BIG_ENDIAN/LITTLE_ENDIAN)
            // ByteBuffer 默认为大端(BIG_ENDIAN)模式 
            buffer.order(ByteOrder.LITTLE_ENDIAN);
        }
        return buffer.getLong();  
    } 

package net.gdface.facelog;

import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.junit.Test;


public class TestSerialVersionUID {
    /**
     * 生成MD5校验码
     * 
     * @param source
     * @return
     */
    static public byte[] getMD5(byte[] source) {
        if (null==source)
            return null;
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            return md.digest(source);
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        return null;
    }
    /**
     * 将16位byte[] 转换为32位的HEX格式的字符串String
     * 
     * @param buffer
     * @return
     */
    static public String toHex(byte buffer[]) {
        if (null==buffer)
            return null;
        StringBuffer sb = new StringBuffer(buffer.length * 2);
        for (int i = 0; i < buffer.length; i++) {
            sb.append(Character.forDigit((buffer[i] & 240) >> 4, 16));
            sb.append(Character.forDigit(buffer[i] & 15, 16));
        }
        return sb.toString();
    }

    /**
     * 将字节数组转为long<br>
     * 如果input为null,或offset指定的剩余数组长度不足8字节则抛出异常
     * @param input 
     * @param offset 起始偏移量
     * @param littleEndian 输入数组是否小端模式
     * @return
     */
    public static long longFrom8Bytes(byte[] input, int offset, boolean littleEndian){
        if(offset <0 || offset+8>input.length)
            throw new IllegalArgumentException(String.format("less than 8 bytes from index %d  is insufficient for long",offset));
        long value=0;
        for(int  count=0;count<8;++count){
            int shift=(littleEndian?count:(7-count))<<3;
            value |=((long)0xff<< shift) & ((long)input[offset+count] << shift);
        }
        return value;
    }

    /**
     * 利用 {@link java.nio.ByteBuffer}实现byte[]转long
     * @param input
     * @param offset 
     * @param littleEndian 输入数组是否小端模式
     * @return
     */
    public static long bytesToLong(byte[] input, int offset, boolean littleEndian) { 
        if(offset <0 || offset+8>input.length)
            throw new IllegalArgumentException(String.format("less than 8 bytes from index %d  is insufficient for long",offset));
        ByteBuffer buffer = ByteBuffer.wrap(input,offset,8);
        if(littleEndian){
            // ByteBuffer.order(ByteOrder) 方法指定字节序,即大小端模式(BIG_ENDIAN/LITTLE_ENDIAN)
            // ByteBuffer 默认为大端(BIG_ENDIAN)模式 
            buffer.order(ByteOrder.LITTLE_ENDIAN);
        }
        return buffer.getLong();  
    } 
    @Test
    public void test() throws IOException {
        String input="net.gdface.facelog.dborm.person.FlPersonBeanBase";
        byte[] md5 = getMD5(input.getBytes());
        System.out.printf("md5 [%s]\n",toHex(md5));
        // 三种方式运算结果对比验证
        DataInputStream dataInput = new DataInputStream(new ByteArrayInputStream(md5)); 
        long l1 = dataInput.readLong();
        long l2 = dataInput.readLong();
        System.out.printf("l1=0x%x l2=0x%x,DataInputStream\n", l1,l2);

        long ln1 = bytesToLong(md5,0, false);
        long ln2 = bytesToLong(md5,8, false);
        System.out.printf("ln1=0x%x ln2=0x%x,ByteBuffer\n", ln1,ln2);

        long ll1 = longFrom8Bytes(md5,0, false);
        long ll2 = longFrom8Bytes(md5,8, false);    
        System.out.printf("ll1=0x%x ll2=0x%x\n", ll1,ll2);
    }
}