Base64算法

import java.io.ByteArrayOutputStream;
import java.io.UnsupportedEncodingException;

public final class Base64 {
 private static final char[] base64EncodeChars = new char[] {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
   'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b',
   'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u',
   'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'};

 private static final byte[] base64DecodeChars = new byte[] {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
   -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
   -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1,
   -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
   21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38,
   39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1};

 
 public static final String encode(String str, String charsetName) {
  return encode(str, charsetName, 0);
 }

 
 public static final String encode(String str, String charsetName, int width) {
  byte[] data = null;
  try {
   data = str.getBytes(charsetName);
  } catch (UnsupportedEncodingException e) {
   e.printStackTrace();
   return null;
  }
  int length = data.length;
  int size = (int) Math.ceil(length * 1.36);
  int splitsize = width > 0 ? size / width : 0;
  StringBuffer sb = new StringBuffer(size + splitsize);
  int r = length % 3;
  int len = length - r;
  int i = 0;
  int c;
  while (i < len) {
   c = (0x000000ff & data[i++]) << 16 | (0x000000ff & data[i++]) << 8 | (0x000000ff & data[i++]);
   sb.append(base64EncodeChars[c >> 18]);
   sb.append(base64EncodeChars[c >> 12 & 0x3f]);
   sb.append(base64EncodeChars[c >> 6 & 0x3f]);
   sb.append(base64EncodeChars[c & 0x3f]);
  }
  if (r == 1) {
   c = 0x000000ff & data[i++];
   sb.append(base64EncodeChars[c >> 2]);
   sb.append(base64EncodeChars[(c & 0x03) << 4]);
   sb.append("==");
  } else if (r == 2) {
   c = (0x000000ff & data[i++]) << 8 | (0x000000ff & data[i++]);
   sb.append(base64EncodeChars[c >> 10]);
   sb.append(base64EncodeChars[c >> 4 & 0x3f]);
   sb.append(base64EncodeChars[(c & 0x0f) << 2]);
   sb.append("=");
  }
  if (splitsize > 0) {
   char split = '/n';
   for (i = width; i < sb.length(); i++) {
    sb.insert(i, split);
    i += width;
   }
  }
  return sb.toString();
 }

 
 public static final String decode(String str, String charsetName) {
  byte[] data = null;
  try {
   data = str.getBytes(charsetName);
  } catch (UnsupportedEncodingException e) {
   e.printStackTrace();
   return null;
  }
  int len = data.length;
  ByteArrayOutputStream buf = new ByteArrayOutputStream((int) (len * 0.67));
  int i = 0;
  int b1, b2, b3, b4;
  while (i < len) {
   
   do {
    if (i >= len) {
     b1 = -1;
     break;
    }
    b1 = base64DecodeChars[data[i++]];
   } while (i < len && b1 == -1);
   if (b1 == -1) {
    break;
   }
   
   do {
    if (i >= len) {
     b2 = -1;
     break;
    }
    b2 = base64DecodeChars[data[i++]];
   } while (i < len && b2 == -1);
   if (b2 == -1) {
    break;
   }
   buf.write((int) ((b1 << 2) | ((b2 & 0x30) >>> 4)));
   
   do {
    if (i >= len) {
     b3 = -1;
     break;
    }
    b3 = data[i++];
    if (b3 == 61) {
     b3 = -1;
     break;
    }
    b3 = base64DecodeChars[b3];
   } while (i < len && b3 == -1);
   if (b3 == -1) {
    break;
   }
   buf.write((int) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));
   
   do {
    if (i >= len) {
     b4 = -1;
     break;
    }
    b4 = data[i++];
    if (b4 == 61) {
     b4 = -1;
     break;
    }
    b4 = base64DecodeChars[b4];
   } while (b4 == -1);
   if (b4 == -1) {
    break;
   }
   buf.write((int) (((b3 & 0x03) << 6) | b4));
  }
  try {
   return buf.toString(charsetName);
  } catch (UnsupportedEncodingException e) {
   e.printStackTrace();
   return null;
  }
 }
}