base64 编解码的 Java 实现

/**
 * Base64Util for Java 
 * cheungmine
 * 2009-11-8
 */
public class Base64Util {
  /**
   * @param args
   */
  public static void main(String[] args) 
  {
    // 源字节数组
    int cb = 0;
    System.out.print("源字节数组:  ");
    
    byte in[] = new byte[100];
    in[cb++]='1';
    in[cb++]='2';
    in[cb++]='3';
    in[cb++]='4';
    in[cb++]='5';
    
    System.out.write(in, 0, cb);
    
    // 计算编码需要的输出字节尺寸
    int cbOut = encodeString( in, cb, null, 0);
    
    // 为输出分配数组
    byte out[] = new byte[cbOut];
    
    // 开始编码
    encodeString( in, cb, out, 0);
        
    // 输出编码内容
    System.out.print("/n编码后内容:  ");
    System.out.write(out, 0, cbOut);
        
    // 计算解码需要的字节
    int cbDec = decodeString(out, cbOut, null);
    
    // 分配解码数组
    byte dec[] = new byte[cbDec];
    
    // 开始解码
    decodeString(out, cbOut, dec);
    
    // 输出解码结果, 这个结果和输出应该一致
    System.out.print("/n解码的结果:  ");   
    System.out.write(dec, 0, cbDec);
  }
  
  /**
   * Translation Table as described in RFC1113
   */
  static String cb64="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  /**
   * Translation Table to decode (created by author)
   */
  static String cd64="|$$$}rstuvwxyz{$$$$$$$>?@ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ[//]^_`abcdefghijklmnopq";
  /**
   * encodeBlock
   *
   * encode 3 8-bit binary bytes (in) as 4 '6-bit' characters (out)
   */
  static void encodeBlock( byte in[], byte out[], int len )
  {
    out[0] = (byte) cb64.charAt( in[0] >> 2 );
      out[1] = (byte) cb64.charAt( ((in[0] & 0x03) << 4) | ((in[1] & 0xf0) >> 4) );
      out[2] = (byte) (len > 1 ? cb64.charAt( ((in[1] & 0x0f) << 2) | ((in[2] & 0xc0) >> 6) ) : '=');
      out[3] = (byte) (len > 2 ? cb64.charAt( in[2] & 0x3f ) : '=');
  }
  
  /**
   * decodeBlock
   *
   * decode 4 '6-bit' characters into 3 8-bit binary bytes
   */
  static void decodeBlock( byte in[], byte out[] )
  {   
      out[ 0 ] = (byte) (in[0] << 2 | in[1] >> 4);
      out[ 1 ] = (byte) (in[1] << 4 | in[2] >> 2);
      out[ 2 ] = (byte) (((in[2] << 6) & 0xc0) | in[3]);
  }
  
  /**
   * encodeString
   *
   * base64 encode bytes
   * by cheungmine
   * outstr is allocated by caller
   * length of encoded string is returned (not including end closing '/0')
   */
  public static int encodeString(  byte instr[], int inlen, byte outstr[], int linesize )
  {
    byte in[] = new byte[3];
    byte out[]= new byte[4];
    
    int inc=0, outc=0, i, len, blocksout = 0;
    
    /* only size of buffer required */
    if (outstr==null){
      if (linesize==0)
        return (inlen%3==0)? ((inlen/3)*4):((inlen/3+1)*4);
      while(inc < inlen) {
        len = 0;        
        for( i = 0; i < 3; i++ ) {
          if (inc < inlen){
            len++;
            inc++;
          }
        }
        if( len>0 ) {
          outc += 4;
          blocksout++;
        }
        if( blocksout >= (linesize/4) || inc==inlen ) {
          if( blocksout>0 ) {
            outc += 2;
          }
          blocksout = 0;
        }
      }
      return outc;
    }
    /* actual encoding below */
      while(inc < inlen) {
          len = 0;        
      for( i = 0; i < 3; i++ ) {
        if (inc < inlen){
          len++;
          in[i] = instr[inc++];
        }
        else{
          in[i] = 0;  // padding with zero
        }
      }
      if(len > 0) {
              encodeBlock( in, out, len );
              for( i = 0; i < 4; i++ ) {
          outstr[outc++] = out[i];
              }
        blocksout++;
          }
      if (linesize > 0){
        if( blocksout >= (linesize/4) || inc==inlen ) {
          if(blocksout > 0) {
            outstr[outc++] = '/r';
            outstr[outc++] = '/n';
          }
          blocksout = 0;
        }
      }
      }
    return outc;
  }
  
  /**
   * add by cheungmine
   * 2009-11-1
   */
  public static int decodeString( byte instr[], int inlen, byte outstr[] )
  {
      byte in[]=new byte[4];
      byte out[]=new byte[3];
      byte v;
      int inc=0, outc=0, i, len;
    /* only size of buffer required */
    if (outstr==null){
      while( inc < inlen ) {
        for( len = 0, i = 0; i < 4 && inc<inlen; i++ ) {
          v = 0;
          while( (inc<=inlen) && (v==0) ) {
            v = (inc < inlen)? instr[inc] : 0;
            inc++;
            v = (byte) ((v < 43 || v > 122) ? 0 : cd64.charAt(v-43));
            if( v>0 ) {
              v = (byte) ((v == '$') ? 0 : v - 61);
            }
          }
          if( inc<=inlen ) {
            len++;
          }
        }
        if( len>1 ) {
          outc += (len-1);
        }
      }
      return outc;
    }
    
      while( inc < inlen ) {
          for( len = 0, i = 0; i < 4 && inc<inlen; i++ ) {
              v = 0;
              while( (inc<=inlen) && (v==0) ) {
          v = (inc < inlen)? instr[inc] : 0;
          inc++;
                  v = (byte) ((v < 43 || v > 122) ? 0 : cd64.charAt(v-43));
                  if( v>0 ) {
                      v = (byte) ((v == '$') ? 0 : v - 61);
                  }
              }
        if( inc<=inlen ) {
                  len++;
                  if( v>0 ) {
                      in[ i ] = (byte) (v - 1);
                  }
              }
              else {
                  in[i] = 0;
              }
          }
          if( len>0 ) {
              decodeBlock( in, out );
              for( i = 0; i < len - 1; i++ ) {
          outstr[outc++] = out[i];
              }
          }
      } 
    return outc;
  }
}