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编码不仅比较简短，同时也具有不可读性，即所编码的数据不会被人用肉眼所直接看到。

import java.io.UnsupportedEncodingException;
import java.util.Arrays;
public class Base64 {
 
 private static final char[] CA = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
               .toCharArray();
       private static final int[] IA = new int[256];
       static {
           Arrays.fill(IA, -1);
           for (int i = 0, iS = CA.length; i < iS; i++)
               IA[CA[i]] = i;
           IA['='] = 0;
       }
  
  
      public final static char[] encodeToChar(byte[] sArr, boolean lineSep) {
          // Check special case
          int sLen = sArr != null ? sArr.length : 0;
          if (sLen == 0)
              return new char[0];
  
          int eLen = (sLen / 3) * 3; // Length of even 24-bits.
          int cCnt = ((sLen - 1) / 3 + 1) << 2; // Returned character count
          int dLen = cCnt + (lineSep ? (cCnt - 1) / 76 << 1 : 0); // Length of
                                                                  // returned
                                                                  // array
          char[] dArr = new char[dLen];
  
          // Encode even 24-bits
          for (int s = 0, d = 0, cc = 0; s < eLen;) {
              // Copy next three bytes into lower 24 bits of int, paying attension
              // to sign.
              int i = (sArr[s++] & 0xff) << 16 | (sArr[s++] & 0xff) << 8
                      | (sArr[s++] & 0xff);
  
              // Encode the int into four chars
              dArr[d++] = CA[(i >>> 18) & 0x3f];
              dArr[d++] = CA[(i >>> 12) & 0x3f];
              dArr[d++] = CA[(i >>> 6) & 0x3f];
              dArr[d++] = CA[i & 0x3f];
  
              // Add optional line separator
              if (lineSep && ++cc == 19 && d < dLen - 2) {
                  dArr[d++] = '\r';
                  dArr[d++] = '\n';
                  cc = 0;
              }
          }
  
          // Pad and encode last bits if source isn't even 24 bits.
          int left = sLen - eLen; // 0 - 2.
          if (left > 0) {
              // Prepare the int
              int i = ((sArr[eLen] & 0xff) << 10)
                      | (left == 2 ? ((sArr[sLen - 1] & 0xff) << 2) : 0);
  
              // Set last four chars
              dArr[dLen - 4] = CA[i >> 12];
              dArr[dLen - 3] = CA[(i >>> 6) & 0x3f];
              dArr[dLen - 2] = left == 2 ? CA[i & 0x3f] : '=';
              dArr[dLen - 1] = '=';
          }
          return dArr;
      }
  
 
      public final static byte[] decode(char[] sArr) {
          // Check special case
          int sLen = sArr != null ? sArr.length : 0;
          if (sLen == 0)
              return new byte[0];
  
          // Count illegal characters (including '\r', '\n') to know what size the
          // returned array will be,
          // so we don't have to reallocate & copy it later.
          int sepCnt = 0; // Number of separator characters. (Actually illegal
                          // characters, but that's a bonus)
          for (int i = 0; i < sLen; i++)
              // If input is "pure" (I.e. no line separators or illegal chars)
              // base64 this loop can be commented out.
              if (IA[sArr[i]] < 0)
                  sepCnt++;
  
          // Check so that legal chars (including '=') are evenly divideable by 4
          // as specified in RFC 2045.
          if ((sLen - sepCnt) % 4 != 0)
              return null;
  
          int pad = 0;
          for (int i = sLen; i > 1 && IA[sArr[--i]] <= 0;)
              if (sArr[i] == '=')
                  pad++;
  
          int len = ((sLen - sepCnt) * 6 >> 3) - pad;
  
          byte[] dArr = new byte[len]; // Preallocate byte[] of exact length
  
          for (int s = 0, d = 0; d < len;) {
              // Assemble three bytes into an int from four "valid" characters.
              int i = 0;
              for (int j = 0; j < 4; j++) { // j only increased if a valid char
                                              // was found.
                  int c = IA[sArr[s++]];
                  if (c >= 0)
                      i |= c << (18 - j * 6);
                  else
                      j--;
              }
              // Add the bytes
              dArr[d++] = (byte) (i >> 16);
              if (d < len) {
                  dArr[d++] = (byte) (i >> 8);
                  if (d < len)
                      dArr[d++] = (byte) i;
              }
          }
          return dArr;
      }
  
 
      public final static byte[] decodeFast(char[] sArr) {
          // Check special case
          int sLen = sArr.length;
          if (sLen == 0)
              return new byte[0];
  
          int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.
  
          // Trim illegal chars from start
          while (sIx < eIx && IA[sArr[sIx]] < 0)
              sIx++;
  
          // Trim illegal chars from end
          while (eIx > 0 && IA[sArr[eIx]] < 0)
              eIx--;
  
          // get the padding count (=) (0, 1 or 2)
          int pad = sArr[eIx] == '=' ? (sArr[eIx - 1] == '=' ? 2 : 1) : 0; // Count
                                                                              // '='
                                                                              // at
                                                                              // end.
          int cCnt = eIx - sIx + 1; // Content count including possible
                                      // separators
          int sepCnt = sLen > 76 ? (sArr[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;
  
          int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded
                                                      // bytes
          byte[] dArr = new byte[len]; // Preallocate byte[] of exact length
  
          // Decode all but the last 0 - 2 bytes.
          int d = 0;
          for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {
              // Assemble three bytes into an int from four "valid" characters.
              int i = IA[sArr[sIx++]] << 18 | IA[sArr[sIx++]] << 12
                      | IA[sArr[sIx++]] << 6 | IA[sArr[sIx++]];
  
              // Add the bytes
              dArr[d++] = (byte) (i >> 16);
              dArr[d++] = (byte) (i >> 8);
              dArr[d++] = (byte) i;
  
              // If line separator, jump over it.
              if (sepCnt > 0 && ++cc == 19) {
                  sIx += 2;
                  cc = 0;
              }
          }
  
          if (d < len) {
              // Decode last 1-3 bytes (incl '=') into 1-3 bytes
              int i = 0;
              for (int j = 0; sIx <= eIx - pad; j++)
                  i |= IA[sArr[sIx++]] << (18 - j * 6);
  
              for (int r = 16; d < len; r -= 8)
                  dArr[d++] = (byte) (i >> r);
          }
  
          return dArr;
      }
  
  
      public final static byte[] encodeToByte(byte[] sArr, boolean lineSep) {
          // Check special case
          int sLen = sArr != null ? sArr.length : 0;
          if (sLen == 0)
              return new byte[0];
  
          int eLen = (sLen / 3) * 3; // Length of even 24-bits.
          int cCnt = ((sLen - 1) / 3 + 1) << 2; // Returned character count
          int dLen = cCnt + (lineSep ? (cCnt - 1) / 76 << 1 : 0); // Length of
                                                                  // returned
                                                                  // array
          byte[] dArr = new byte[dLen];
  
          // Encode even 24-bits
          for (int s = 0, d = 0, cc = 0; s < eLen;) {
              // Copy next three bytes into lower 24 bits of int, paying attension
              // to sign.
              int i = (sArr[s++] & 0xff) << 16 | (sArr[s++] & 0xff) << 8
                      | (sArr[s++] & 0xff);
  
              // Encode the int into four chars
              dArr[d++] = (byte) CA[(i >>> 18) & 0x3f];
              dArr[d++] = (byte) CA[(i >>> 12) & 0x3f];
              dArr[d++] = (byte) CA[(i >>> 6) & 0x3f];
              dArr[d++] = (byte) CA[i & 0x3f];
  
              // Add optional line separator
              if (lineSep && ++cc == 19 && d < dLen - 2) {
                  dArr[d++] = '\r';
                  dArr[d++] = '\n';
                  cc = 0;
              }
          }
  
          // Pad and encode last bits if source isn't an even 24 bits.
          int left = sLen - eLen; // 0 - 2.
          if (left > 0) {
              // Prepare the int
              int i = ((sArr[eLen] & 0xff) << 10)
                      | (left == 2 ? ((sArr[sLen - 1] & 0xff) << 2) : 0);
  
              // Set last four chars
              dArr[dLen - 4] = (byte) CA[i >> 12];
              dArr[dLen - 3] = (byte) CA[(i >>> 6) & 0x3f];
              dArr[dLen - 2] = left == 2 ? (byte) CA[i & 0x3f] : (byte) '=';
              dArr[dLen - 1] = '=';
          }
          return dArr;
      }
  
 
      public final static byte[] decode(byte[] sArr) {
          // Check special case
          int sLen = sArr.length;
  
          // Count illegal characters (including '\r', '\n') to know what size the
          // returned array will be,
          // so we don't have to reallocate & copy it later.
          int sepCnt = 0; // Number of separator characters. (Actually illegal
                          // characters, but that's a bonus)
          for (int i = 0; i < sLen; i++)
              // If input is "pure" (I.e. no line separators or illegal chars)
              // base64 this loop can be commented out.
              if (IA[sArr[i] & 0xff] < 0)
                  sepCnt++;
  
          // Check so that legal chars (including '=') are evenly divideable by 4
          // as specified in RFC 2045.
          if ((sLen - sepCnt) % 4 != 0)
              return null;
  
          int pad = 0;
          for (int i = sLen; i > 1 && IA[sArr[--i] & 0xff] <= 0;)
              if (sArr[i] == '=')
                  pad++;
  
          int len = ((sLen - sepCnt) * 6 >> 3) - pad;
  
          byte[] dArr = new byte[len]; // Preallocate byte[] of exact length
  
          for (int s = 0, d = 0; d < len;) {
              // Assemble three bytes into an int from four "valid" characters.
              int i = 0;
              for (int j = 0; j < 4; j++) { // j only increased if a valid char
                                              // was found.
                  int c = IA[sArr[s++] & 0xff];
                  if (c >= 0)
                      i |= c << (18 - j * 6);
                  else
                      j--;
              }
  
              // Add the bytes
              dArr[d++] = (byte) (i >> 16);
              if (d < len) {
                  dArr[d++] = (byte) (i >> 8);
                  if (d < len)
                      dArr[d++] = (byte) i;
              }
          }
  
          return dArr;
      }
 
      public final static byte[] decodeFast(byte[] sArr) {
          // Check special case
          int sLen = sArr.length;
          if (sLen == 0)
              return new byte[0];
  
          int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.
  
          // Trim illegal chars from start
          while (sIx < eIx && IA[sArr[sIx] & 0xff] < 0)
              sIx++;
  
          // Trim illegal chars from end
          while (eIx > 0 && IA[sArr[eIx] & 0xff] < 0)
              eIx--;
  
          // get the padding count (=) (0, 1 or 2)
          int pad = sArr[eIx] == '=' ? (sArr[eIx - 1] == '=' ? 2 : 1) : 0; // Count
                                                                              // '='
                                                                              // at
                                                                              // end.
          int cCnt = eIx - sIx + 1; // Content count including possible
                                      // separators
          int sepCnt = sLen > 76 ? (sArr[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;
  
          int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded
                                                      // bytes
          byte[] dArr = new byte[len]; // Preallocate byte[] of exact length
  
          // Decode all but the last 0 - 2 bytes.
          int d = 0;
          for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {
              // Assemble three bytes into an int from four "valid" characters.
              int i = IA[sArr[sIx++]] << 18 | IA[sArr[sIx++]] << 12
                      | IA[sArr[sIx++]] << 6 | IA[sArr[sIx++]];
  
              // Add the bytes
              dArr[d++] = (byte) (i >> 16);
              dArr[d++] = (byte) (i >> 8);
              dArr[d++] = (byte) i;
  
              // If line separator, jump over it.
              if (sepCnt > 0 && ++cc == 19) {
                  sIx += 2;
                  cc = 0;
              }
          }
  
          if (d < len) {
              // Decode last 1-3 bytes (incl '=') into 1-3 bytes
              int i = 0;
              for (int j = 0; sIx <= eIx - pad; j++)
                  i |= IA[sArr[sIx++]] << (18 - j * 6);
  
              for (int r = 16; d < len; r -= 8)
                  dArr[d++] = (byte) (i >> r);
          }
  
          return dArr;
      }
 
      public final static String encodeToString(byte[] sArr, boolean lineSep) {
          // Reuse char[] since we can't create a String incrementally anyway and
          // StringBuffer/Builder would be slower.
          return new String(encodeToChar(sArr, lineSep));
      }
     
      public final static String encode(String s) {
          // Reuse char[] since we can't create a String incrementally anyway and
          // StringBuffer/Builder would be slower.
          try {
              return new String(encodeToChar(s.getBytes("UTF-8"), false));
          } catch (UnsupportedEncodingException e) {
              System.err.println("Base64 encoding error: " + e.getMessage());
              e.printStackTrace();
          }
          return null;
      }
  
      public final static byte[] decode(String str, boolean used) {
          // Check special case
          int sLen = str != null ? str.length() : 0;
          if (sLen == 0)
              return new byte[0];
  
          // Count illegal characters (including '\r', '\n') to know what size the
          // returned array will be,
          // so we don't have to reallocate & copy it later.
          int sepCnt = 0; // Number of separator characters. (Actually illegal
                          // characters, but that's a bonus)
          for (int i = 0; i < sLen; i++)
             // If input is "pure" (I.e. no line separators or illegal chars)
              // base64 this loop can be commented out.
              if (IA[str.charAt(i)] < 0)
                  sepCnt++;
  
          // Check so that legal chars (including '=') are evenly divideable by 4
          // as specified in RFC 2045.
          if ((sLen - sepCnt) % 4 != 0)
              return null;
  
          // Count '=' at end
          int pad = 0;
          for (int i = sLen; i > 1 && IA[str.charAt(--i)] <= 0;)
              if (str.charAt(i) == '=')
                  pad++;
  
          int len = ((sLen - sepCnt) * 6 >> 3) - pad;
  
          byte[] dArr = new byte[len]; // Preallocate byte[] of exact length
  
          for (int s = 0, d = 0; d < len;) {
              // Assemble three bytes into an int from four "valid" characters.
              int i = 0;
              for (int j = 0; j < 4; j++) { // j only increased if a valid char
                                              // was found.
                  int c = IA[str.charAt(s++)];
                  if (c >= 0)
                      i |= c << (18 - j * 6);
                  else
                      j--;
              }
              // Add the bytes
              dArr[d++] = (byte) (i >> 16);
              if (d < len) {
                  dArr[d++] = (byte) (i >> 8);
                  if (d < len)
                      dArr[d++] = (byte) i;
              }
          }
          return dArr;
      }

      public final static byte[] decodeFast(String s) {
          // Check special case
          int sLen = s.length();
          if (sLen == 0)
              return new byte[0];
  
          int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.
  
          // Trim illegal chars from start
          while (sIx < eIx && IA[s.charAt(sIx) & 0xff] < 0)
              sIx++;
  
          // Trim illegal chars from end
          while (eIx > 0 && IA[s.charAt(eIx) & 0xff] < 0)
              eIx--;
  
          // get the padding count (=) (0, 1 or 2)
          int pad = s.charAt(eIx) == '=' ? (s.charAt(eIx - 1) == '=' ? 2 : 1) : 0; // Count
                                                                                      // '='
                                                                                      // at
                                                                                      // end.
          int cCnt = eIx - sIx + 1; // Content count including possible
                                      // separators
          int sepCnt = sLen > 76 ? (s.charAt(76) == '\r' ? cCnt / 78 : 0) << 1
                  : 0;
  
          int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded
                                                      // bytes
          byte[] dArr = new byte[len]; // Preallocate byte[] of exact length
  
          // Decode all but the last 0 - 2 bytes.
          int d = 0;
          for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {
              // Assemble three bytes into an int from four "valid" characters.
              int i = IA[s.charAt(sIx++)] << 18 | IA[s.charAt(sIx++)] << 12
                      | IA[s.charAt(sIx++)] << 6 | IA[s.charAt(sIx++)];
  
              // Add the bytes
              dArr[d++] = (byte) (i >> 16);
              dArr[d++] = (byte) (i >> 8);
              dArr[d++] = (byte) i;
  
              // If line separator, jump over it.
              if (sepCnt > 0 && ++cc == 19) {
                  sIx += 2;
                  cc = 0;
              }
          }
  
          if (d < len) {
              // Decode last 1-3 bytes (incl '=') into 1-3 bytes
              int i = 0;
              for (int j = 0; sIx <= eIx - pad; j++)
                  i |= IA[s.charAt(sIx++)] << (18 - j * 6);
  
              for (int r = 16; d < len; r -= 8)
                  dArr[d++] = (byte) (i >> r);
          }
  
          return dArr;
      }
      public static String decode(String s) throws UnsupportedEncodingException {
          return new String(Base64.decodeFast(s), "utf-8");
      }
     
      public static void main(String[] args) throws UnsupportedEncodingException {
       String str="测试";
       String encode=encode(str);
       System.out.println(encode);
       String decode=decode(encode);
       System.out.println(decode);
      }
}

运行结果如下：

5rWL6K+V
测试