Base64編碼

       Base64是網絡上最常見的用於傳輸8Bit字節代碼的編碼方式之一，大家可以查看RFC2045～RFC2049，上面有MIME的詳細規範。Base64編碼可用於在HTTP環境下傳遞較長的標識信息。採用Base64編碼具有不可讀性，即所編碼的數據不會被人用肉眼所直接看到。設計此種編碼是爲了使二進制數據可以通過非純 8-bit 的傳輸層傳輸，例如電子郵件的主體。

Base64編碼的java代碼示例：

 

package com.zhuifeng.util;
/**
 * 
 * @author guoxk
 *
 * @version 創建時間 2016年1月8日 上午10:19:05
 *
 * 類描述：base64加密解密工具類
 *
 */
public class Base64Coder
{
	private static char[] map1 = new char[64];
	static
	{
		int i = 0;
		for (char c = 'A'; c <= 'Z'; c++)
			map1[i++] = c;
		for (char c = 'a'; c <= 'z'; c++)
			map1[i++] = c;
		for (char c = '0'; c <= '9'; c++)
			map1[i++] = c;
		map1[i++] = '+';
		map1[i++] = '/';
	}

	// Mapping table from Base64 characters to 6-bit nibbles.
	private static byte[] map2 = new byte[128];
	static
	{
		for (int i = 0; i < map2.length; i++)
			map2[i] = -1;
		for (int i = 0; i < 64; i++)
			map2[map1[i]] = (byte) i;
	}
	/**
	 * @author guoxk
	 *
	 * 方法描述：加密
	 * @param s 明文
	 * @return 密文
	 */
	public static String encode(String s)
	{
		return new String(encode(s.getBytes()));
	}

	public static char[] encode(byte[] in)
	{
		return encode(in, in.length);
	}

	private static char[] encode(byte[] in, int iLen)
	{
		int oDataLen = (iLen * 4 + 2) / 3; // output length without padding
		int oLen = ((iLen + 2) / 3) * 4; // output length including padding
		char[] out = new char[oLen];
		int ip = 0;
		int op = 0;
		while (ip < iLen)
		{
			int i0 = in[ip++] & 0xff;
			int i1 = ip < iLen ? in[ip++] & 0xff : 0;
			int i2 = ip < iLen ? in[ip++] & 0xff : 0;
			int o0 = i0 >>> 2;
			int o1 = ((i0 & 3) << 4) | (i1 >>> 4);
			int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
			int o3 = i2 & 0x3F;
			out[op++] = map1[o0];
			out[op++] = map1[o1];
			out[op] = op < oDataLen ? map1[o2] : '=';
			op++;
			out[op] = op < oDataLen ? map1[o3] : '=';
			op++;
		}
		return out;
	}

	/**
	 * @author guoxk
	 *
	 * 方法描述：解密
	 * @param s 密文
	 * @return  明文
	 */
	public static String decode(String s)
	{
		return new String(decode(s.toCharArray()));
	}
	public static byte[] decode(char[] in)
	{
		int iLen = in.length;
		if (iLen % 4 != 0)
			throw new IllegalArgumentException("Length of Base64 encoded input string is not a multiple of 4.");
		while (iLen > 0 && in[iLen - 1] == '=')
			iLen--;
		int oLen = (iLen * 3) / 4;
		byte[] out = new byte[oLen];
		int ip = 0;
		int op = 0;
		while (ip < iLen)
		{
			int i0 = in[ip++];
			int i1 = in[ip++];
			int i2 = ip < iLen ? in[ip++] : 'A';
			int i3 = ip < iLen ? in[ip++] : 'A';
			if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
				throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
			int b0 = map2[i0];
			int b1 = map2[i1];
			int b2 = map2[i2];
			int b3 = map2[i3];
			if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
				throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
			int o0 = (b0 << 2) | (b1 >>> 4);
			int o1 = ((b1 & 0xf) << 4) | (b2 >>> 2);
			int o2 = ((b2 & 3) << 6) | b3;
			out[op++] = (byte) o0;
			if (op < oLen)
				out[op++] = (byte) o1;
			if (op < oLen)
				out[op++] = (byte) o2;
		}
		return out;
	}

	private Base64Coder()
	{
	}

	public static void main(String[] args)
	{
		System.out.println(Base64Coder.decode("w/fOxA=="));//解密
		System.out.println(Base64Coder.encode("明文"));//加密
	}
}