java Base64 原码

package com.onepay.util;
import java.io.ByteArrayOutputStream;  
import java.io.IOException;  
import java.io.OutputStream;  
public class Base64 {
      private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();  
      
        public static String encode(byte[] data) {  
            int start = 0;  
            int len = data.length;  
            StringBuffer buf = new StringBuffer(data.length * 3 / 2);  
      
            int end = len - 3;  
            int i = start;  
            int n = 0;  
      
            while (i <= end) {  
                int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 0x0ff) << 8) | (((int) data[i + 2]) & 0x0ff);  
      
                buf.append(legalChars[(d >> 18) & 63]);  
                buf.append(legalChars[(d >> 12) & 63]);  
                buf.append(legalChars[(d >> 6) & 63]);  
                buf.append(legalChars[d & 63]);  
      
                i += 3;  
      
                if (n++ >= 14) {  
                    n = 0;  
                    buf.append(" ");  
                }  
            }  
      
            if (i == start + len - 2) {  
                int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 255) << 8);  
      
                buf.append(legalChars[(d >> 18) & 63]);  
                buf.append(legalChars[(d >> 12) & 63]);  
                buf.append(legalChars[(d >> 6) & 63]);  
                buf.append("=");  
            } else if (i == start + len - 1) {  
                int d = (((int) data[i]) & 0x0ff) << 16;  
      
                buf.append(legalChars[(d >> 18) & 63]);  
                buf.append(legalChars[(d >> 12) & 63]);  
                buf.append("==");  
            }  
      
            return buf.toString();  
        }  
      
        private static int decode(char c) {  
            if (c >= 'A' && c <= 'Z')  
                return ((int) c) - 65;  
            else if (c >= 'a' && c <= 'z')  
                return ((int) c) - 97 + 26;  
            else if (c >= '0' && c <= '9')  
                return ((int) c) - 48 + 26 + 26;  
            else  
                switch (c) {  
                case '+':  
                    return 62;  
                case '/':  
                    return 63;  
                case '=':  
                    return 0;  
                default:  
                    throw new RuntimeException("unexpected code: " + c);  
                }  
        }  
      
        /** 
         * Decodes the given Base64 encoded String to a new byte array. The byte array holding the decoded data is returned. 
         */  
      
        public static byte[] decode(String s) {  
      
            ByteArrayOutputStream bos = new ByteArrayOutputStream();  
            try {  
                decode(s, bos);  
            } catch (IOException e) {  
                throw new RuntimeException();  
            }  
            byte[] decodedBytes = bos.toByteArray();  
            try {  
                bos.close();  
                bos = null;  
            } catch (IOException ex) {  
                System.err.println("Error while decoding BASE64: " + ex.toString());  
            }  
            return decodedBytes;  
        }  
      
        private static void decode(String s, OutputStream os) throws IOException {  
            int i = 0;  
      
            int len = s.length();  
      
            while (true) {  
                while (i < len && s.charAt(i) <= ' ')  
                    i++;  
      
                if (i == len)  
                    break;  
      
                int tri = (decode(s.charAt(i)) << 18) + (decode(s.charAt(i + 1)) << 12) + (decode(s.charAt(i + 2)) << 6) + (decode(s.charAt(i + 3)));  
      
                os.write((tri >> 16) & 255);  
                if (s.charAt(i + 2) == '=')  
                    break;  
                os.write((tri >> 8) & 255);  
                if (s.charAt(i + 3) == '=')  
                    break;  
                os.write(tri & 255);  
      
                i += 4;  
            }  
        }  
}