第十一篇： JAVA加密解密之Base64

Base64是网络上最常见的用于传输8Bit字节代码的编码方式之一，大家可以查看RFC2045～RFC2049，上面有MIME的详细规范。Base64编码可用于在HTTP环境下传递较长的标识信息。例如，在Java Persistence系统hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为128-bit的UUID）编码为一个字符串，用作HTTP表单和HTTP GET URL中的参数。在其他应用程序中，也常常需要把二进制数据编码为适合放在URL（包括隐藏表单域）中的形式。此时，采用Base64编码具有不可读性，即所编码的数据不会被人用肉眼所直接看到。

package com.jianggujin.codec;/** * Base64 *  * @author jianggujin * */public class HQBase64{   private final byte[] EMPTY = new byte[0];   private final int BASELENGTH = 128;   private final int LOOKUPLENGTH = 64;   private final int TWENTYFOURBITGROUP = 24;   private final int EIGHTBIT = 8;   private final int SIXTEENBIT = 16;   private final int FOURBYTE = 4;   private final int SIGN = -128;   private final char PAD = '=';   private final byte[] base64Alphabet = new byte[BASELENGTH];   private final byte[] lookUpBase64Alphabet = new byte[LOOKUPLENGTH];   private static HQBase64 base64 = new HQBase64();   public static HQBase64 getInstance()   {      return base64;   }   private HQBase64()   {      for (int i = 0; i < BASELENGTH; ++i)      {         base64Alphabet[i] = -1;      }      for (int i = 'Z'; i >= 'A'; i--)      {         base64Alphabet[i] = (byte) (i - 'A');      }      for (int i = 'z'; i >= 'a'; i--)      {         base64Alphabet[i] = (byte) (i - 'a' + 26);      }      for (int i = '9'; i >= '0'; i--)      {         base64Alphabet[i] = (byte) (i - '0' + 52);      }      base64Alphabet['+'] = 62;      base64Alphabet['/'] = 63;      for (int i = 0; i <= 25; i++)      {         lookUpBase64Alphabet[i] = (byte) ('A' + i);      }      for (int i = 26, j = 0; i <= 51; i++, j++)      {         lookUpBase64Alphabet[i] = (byte) ('a' + j);      }      for (int i = 52, j = 0; i <= 61; i++, j++)      {         lookUpBase64Alphabet[i] = (byte) ('0' + j);      }      lookUpBase64Alphabet[62] = (char) '+';      lookUpBase64Alphabet[63] = (char) '/';   }   private boolean isWhiteSpace(byte octect)   {      return (octect == 0x20 || octect == 0xd || octect == 0xa || octect == 0x9);   }   private boolean isPad(byte octect)   {      return (octect == PAD);   }   private boolean isData(byte octect)   {      return (octect < BASELENGTH && base64Alphabet[octect] != -1);   }   private int removeWhiteSpace(byte[] data)   {      if (data == null)      {         return 0;      }      int newSize = 0;      int len = data.length;      for (int i = 0; i < len; i++)      {         if (!isWhiteSpace(data[i]))         {            data[newSize++] = data[i];         }      }      return newSize;   }   public byte[] encode(byte[] binaryData)   {      if (binaryData == null)      {         return null;      }      int lengthDataBits = binaryData.length * EIGHTBIT;      if (lengthDataBits == 0)      {         return EMPTY;      }      int fewerThan24bits = lengthDataBits % TWENTYFOURBITGROUP;      int numberTriplets = lengthDataBits / TWENTYFOURBITGROUP;      int numberQuartet = fewerThan24bits != 0 ? numberTriplets + 1 : numberTriplets;      byte encodedData[] = null;      encodedData = new byte[numberQuartet * 4];      byte k = 0, l = 0, b1 = 0, b2 = 0, b3 = 0;      int encodedIndex = 0;      int dataIndex = 0;      for (int i = 0; i < numberTriplets; i++)      {         b1 = binaryData[dataIndex++];         b2 = binaryData[dataIndex++];         b3 = binaryData[dataIndex++];         l = (byte) (b2 & 0x0f);         k = (byte) (b1 & 0x03);         byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);         byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0);         byte val3 = ((b3 & SIGN) == 0) ? (byte) (b3 >> 6) : (byte) ((b3) >> 6 ^ 0xfc);         encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];         encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];         encodedData[encodedIndex++] = lookUpBase64Alphabet[(l << 2) | val3];         encodedData[encodedIndex++] = lookUpBase64Alphabet[b3 & 0x3f];      }      if (fewerThan24bits == EIGHTBIT)      {         b1 = binaryData[dataIndex];         k = (byte) (b1 & 0x03);         byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);         encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];         encodedData[encodedIndex++] = lookUpBase64Alphabet[k << 4];         encodedData[encodedIndex++] = PAD;         encodedData[encodedIndex++] = PAD;      }      else if (fewerThan24bits == SIXTEENBIT)      {         b1 = binaryData[dataIndex];         b2 = binaryData[dataIndex + 1];         l = (byte) (b2 & 0x0f);         k = (byte) (b1 & 0x03);         byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);         byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0);         encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];         encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];         encodedData[encodedIndex++] = lookUpBase64Alphabet[l << 2];         encodedData[encodedIndex++] = PAD;      }      return encodedData;   }   public byte[] decode(byte[] encoded)   {      if (encoded == null)      {         return null;      }      byte[] base64Data = encoded;      int len = removeWhiteSpace(base64Data);      if (len % FOURBYTE != 0)      {         return null;      }      int numberQuadruple = (len / FOURBYTE);      if (numberQuadruple == 0)      {         return new byte[0];      }      byte decodedData[] = null;      byte b1 = 0, b2 = 0, b3 = 0, b4 = 0;      byte d1 = 0, d2 = 0, d3 = 0, d4 = 0;      int i = 0;      int encodedIndex = 0;      int dataIndex = 0;      decodedData = new byte[(numberQuadruple) * 3];      for (; i < numberQuadruple - 1; i++)      {         if (!isData((d1 = base64Data[dataIndex++])) || !isData((d2 = base64Data[dataIndex++]))               || !isData((d3 = base64Data[dataIndex++])) || !isData((d4 = base64Data[dataIndex++])))         {            return null;         }         b1 = base64Alphabet[d1];         b2 = base64Alphabet[d2];         b3 = base64Alphabet[d3];         b4 = base64Alphabet[d4];         decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);         decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));         decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);      }      if (!isData((d1 = base64Data[dataIndex++])) || !isData((d2 = base64Data[dataIndex++])))      {         return null;// if found "no data" just return null      }      b1 = base64Alphabet[d1];      b2 = base64Alphabet[d2];      d3 = base64Data[dataIndex++];      d4 = base64Data[dataIndex++];      if (!isData((d3)) || !isData((d4)))      {         if (isPad(d3) && isPad(d4))         {            if ((b2 & 0xf) != 0)            {               return null;            }            byte[] tmp = new byte[i * 3 + 1];            System.arraycopy(decodedData, 0, tmp, 0, i * 3);            tmp[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);            return tmp;         }         else if (!isPad(d3) && isPad(d4))         {            b3 = base64Alphabet[d3];            if ((b3 & 0x3) != 0)// last 2 bits should be zero            {               return null;            }            byte[] tmp = new byte[i * 3 + 2];            System.arraycopy(decodedData, 0, tmp, 0, i * 3);            tmp[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);            tmp[encodedIndex] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));            return tmp;         }         else         {            return null;         }      }      else      {         b3 = base64Alphabet[d3];         b4 = base64Alphabet[d4];         decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);         decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));         decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);      }      return decodedData;   }   public String encodeToString(byte[] binaryData)   {      return new String(encode(binaryData));   }   public String encodeToString(String data)   {      return new String(encode(data.getBytes()));   }   public byte[] decodeString(String encoded)   {      return decode(encoded.getBytes());   }}
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编写一个测试类来测试一下：

import org.junit.Test;import com.jianggujin.codec.HQBase64;public class Base64Test{   HQBase64 base64 = HQBase64.getInstance();   @Test   public void encode()   {      byte[] data = "jianggujin".getBytes();      String result = base64.encodeToString(data);      System.err.println(result);      System.err.println(new String(base64.decodeString(result)));   }}
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运行结果： 
amlhbmdndWppbg== 
jianggujin