HexDump.java解析

从包名我们可以看出该类并没有对应用开发者开放，也就是说在google开放的Android API文档中并没有该类的相关介绍；好在Android系统源码是开源的，因此我在解决framework中问题的时候发现了这个工具类，由于工作原因一直没有回头在细细的领会这个工具类的精髓，因此今天花点时间对这个类进行全面的分析一遍，以备不时之需。

首先分析之前，我们需要了解该类使用来进行16禁止转换的，我之前也写过相关的工具类，但是去了解Google的精神还是有必要的。

package com.android.internal.util;

public class HexDump
{
    private final static char[] HEX_DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };//十六进制的组成元素
    
    public static String dumpHexString(byte[] array)
    {
        return dumpHexString(array, 0, array.length);
    }
    
    public static String dumpHexString(byte[] array, int offset, int length)
    {
        StringBuilder result = new StringBuilder();
        
        byte[] line = new byte[16];
        int lineIndex = 0;
        
        result.append(" 0x");
        result.append(toHexString(offset));
        
        for (int i = offset ; i < offset + length ; i++)
        {
            if (lineIndex == 16)
            {
                result.append(" ");
                
                for (int j = 0 ; j < 16 ; j++)
                {
                    if (line[j] > ' ' && line[j] < '~')
                    {
                        result.append(new String(line, j, 1));
                    }
                    else
                    {
                        result.append(".");
                    }
                }
                
                result.append(" 0x");
                result.append(toHexString(i));
                lineIndex = 0;
            }
            
            byte b = array[i];
            result.append(" ");
            result.append(HEX_DIGITS[(b >>> 4) & 0x0F]);
            result.append(HEX_DIGITS[b & 0x0F]);
            
            line[lineIndex++] = b;
        }
        
        if (lineIndex != 16)
        {
            int count = (16 - lineIndex) * 3;
            count++;
            for (int i = 0 ; i < count ; i++)
            {
                result.append(" ");
            }
            
            for (int i = 0 ; i < lineIndex ; i++)
            {
                if (line[i] > ' ' && line[i] < '~')
                {
                    result.append(new String(line, i, 1));
                }
                else
                {
                    result.append(".");
                }
            }
        }
        
        return result.toString();
    }
    
    public static String toHexString(byte b)
    {
        return toHexString(toByteArray(b));
    }

    public static String toHexString(byte[] array)
    {
        return toHexString(array, 0, array.length);
    }
    
    public static String toHexString(byte[] array, int offset, int length)
    {
        char[] buf = new char[length * 2];

        int bufIndex = 0;
        for (int i = offset ; i < offset + length; i++)
        {
            byte b = array[i];
            buf[bufIndex++] = HEX_DIGITS[(b >>> 4) & 0x0F];
            buf[bufIndex++] = HEX_DIGITS[b & 0x0F];
        }

        return new String(buf);        
    }
    
    public static String toHexString(int i)
    {
        return toHexString(toByteArray(i));
    }
    
    public static byte[] toByteArray(byte b)
    {
        byte[] array = new byte[1];
        array[0] = b;
        return array;
    }
    
    public static byte[] toByteArray(int i)
    {
        byte[] array = new byte[4];
        
        array[3] = (byte)(i & 0xFF);
        array[2] = (byte)((i >> 8) & 0xFF);
        array[1] = (byte)((i >> 16) & 0xFF);
        array[0] = (byte)((i >> 24) & 0xFF);
        
        return array;
    }
    
    private static int toByte(char c)
    {
        if (c >= '0' && c <= '9') return (c - '0');
        if (c >= 'A' && c <= 'F') return (c - 'A' + 10);
        if (c >= 'a' && c <= 'f') return (c - 'a' + 10);

        throw new RuntimeException ("Invalid hex char '" + c + "'");
    }
    
    public static byte[] hexStringToByteArray(String hexString)
    {
        int length = hexString.length();
        byte[] buffer = new byte[length / 2];

        for (int i = 0 ; i < length ; i += 2)
        {
            buffer[i / 2] = (byte)((toByte(hexString.charAt(i)) << 4) | toByte(hexString.charAt(i+1)));
        }
        
        return buffer;
    }    
}