Base64

import java.io.ByteArrayOutputStream; 

import java.io.IOException; 

import java.io.OutputStream; 

 

 

 

public class Base64 { 

    private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray(); 

    /**

     * data[]进行编码

     * @param data

     * @return

     */ 

        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; 

            } 

        } 

         

}