Java：Base64编解码

/* ------------------------------------------------------ *
 文件名称：Base64.java

作者：秦建辉

MSN：[e-mail]
QQ：36748897

博客：http://blog.csdn.net/jhqin

开发环境：
    eclipse-jee-indigo-SR2
	jdk-7u4-windows-x64
版本历史：
    V1.0	2012年05月30日
			Base64编解码
 * ------------------------------------------------------ */
package net.csdn.blog.jhqin.util;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

public class Base64
{
	private final static String DATA_BIN2ASCII = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
	
	public static String encodeBase64String(byte[] binaryData)
	{
		if(binaryData == null) return null;
		
		// 每3个字节转换成4个字符
		int Length = ((binaryData.length + 2) / 3) << 2;
		StringBuilder sb = new StringBuilder(Length);
		
		int Index = 0;
		for(int i = binaryData.length; i > 0; i -= 3)
		{		
			if(i >= 3)
			{	// 将3字节数据转换成4个ASCII字符
				int b0 = binaryData[Index++] & 0xFF;
				int b1 = binaryData[Index++] & 0xFF;
				int b2 = binaryData[Index++] & 0xFF;
				
				sb.append(DATA_BIN2ASCII.charAt(b0 >> 2));
				sb.append(DATA_BIN2ASCII.charAt(((b0 << 4) | (b1 >> 4)) & 0x3F));
				sb.append(DATA_BIN2ASCII.charAt(((b1 << 2) | (b2 >> 6)) & 0x3F));
				sb.append(DATA_BIN2ASCII.charAt(b2 & 0x3F));
			}
			else
			{
				int b0 = binaryData[Index++] & 0xFF;
				int b1;
				if(i == 2)
					b1 = binaryData[Index++] & 0xFF;
				else
					b1 = 0;
				
				sb.append(DATA_BIN2ASCII.charAt(b0 >> 2));
				sb.append(DATA_BIN2ASCII.charAt(((b0 << 4) | (b1 >> 4)) & 0x3F));
				if(i == 1)
					sb.append('=');
				else
					sb.append(DATA_BIN2ASCII.charAt((b1 << 2) & 0x3F));
				sb.append('=');
			}
		}
		
		return sb.toString();
	}
	
	// private final static int B64_ERROR = -1;		// 0xFF 错误字符
	// private final static int B64_EOLN = -16;		// 0xF0 换行\n
	// private final static int B64_CR = -15;		// 0xF1 回车\r
	// private final static int B64_EOF = -14;		// 0xF2 连字符-		
	private final static int B64_WS = -32;			// 0xE0 跳格或者空格（\t、space）
	private final static int B64_NOT_BASE64 = -13;	// 0xF3 空白字符、回车换行字符、连字符
	
	private final static byte[] DATA_ASCII2BIN = {
		  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1, -32, -16,  -1,  -1, -15,  -1,  -1,
		  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,
		 -32,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,  -1,0x3E,  -1, -14,  -1,0x3F,
		0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B,0x3C,0x3D,  -1,  -1,  -1,0x00,  -1,  -1,
		  -1,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,
		0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,  -1,  -1,  -1,  -1,  -1,
		  -1,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28,
		0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31,0x32,0x33,  -1,  -1,  -1,  -1,  -1
	};
	
	public static byte[] decodeBase64(String base64String) 
			throws IOException
	{
		if(base64String == null || base64String.isEmpty())return null;
		
		// 去除头部空白字符
		int upIndex = 0;
		int downIndex = base64String.length() - 1;		
		while(upIndex <= downIndex)
		{
			int charValue = base64String.charAt(upIndex);
			if(charValue >= 0x80)
				throw new IllegalArgumentException();	// 不是ASCII字符
			
			if(DATA_ASCII2BIN[charValue] == B64_WS) 
				upIndex++; 
			else
				break;
		}
		
		// 去除尾部的空白字符、回车换行字符、连字符
		while(downIndex >= upIndex)
		{
			int charValue = base64String.charAt(downIndex);
			if(charValue >= 0x80)
				throw new IllegalArgumentException();	// 不是ASCII字符
			if((DATA_ASCII2BIN[charValue] | 0x13) == B64_NOT_BASE64) 
				downIndex--; 
			else
				break;				
		}
		
		// 有效长度必须为4的倍数
		int length = downIndex - upIndex + 1;
		if((length < 4) || (length % 4 != 0))
			throw new IllegalArgumentException();
		
		// 转换字符串到字节数组
		ByteArrayOutputStream memoryStream = null;
		try
		{
			memoryStream = new ByteArrayOutputStream((length >> 2) * 3);			
			int[] room = new int[4];
			while(upIndex <= downIndex)
			{
				int j = 0;
				for(; j < 4; j++)
				{
					int charValue = base64String.charAt(upIndex++);
					if(charValue >= 0x80)
						throw new IllegalArgumentException();
					
					if(charValue == '=') break;	// 填充字符
					
					charValue = DATA_ASCII2BIN[charValue];
					if(charValue < 0)
						throw new IllegalArgumentException();
					room[j] = charValue;
				}
				
				if(j == 4)
				{
					memoryStream.write((room[0] << 2) | (room[1] >> 4));
					memoryStream.write((room[1] << 4) | (room[2] >> 2));
					memoryStream.write((room[2] << 6) | room[3]);					
				}
				else if(j == 3)
				{	// 有1个填充字节
					memoryStream.write((room[0] << 2) | (room[1] >> 4));
					memoryStream.write((room[1] << 4) | (room[2] >> 2));
					break;
				}
				else if(j == 2)
				{	// 有2个填充字节
					memoryStream.write((room[0] << 2) | (room[1] >> 4));
					break;
				}
				else
					throw new IllegalArgumentException();		
			}
			
			return memoryStream.toByteArray();
		} 		
		finally
		{
			if(memoryStream != null) memoryStream.close();
		}		
	}
}