1. public class Base64Utils {
    3.     private static final String CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    5.     public static String base64(String str) {
    6.         return base64(str == null ? null : str.getBytes());
    7.     }
    9.     public static String base64(byte[] bytes) {
    10.         if (bytes == null || bytes.length == 0) {
    11.             return "";
    12.         }
    14.         int length = bytes.length;
    15.         int gSize = 3;
    16.         int group = (length - 1) / gSize + 1;
    17.         int[] arr = new int[4];
    18.         byte[] result = new byte[group * 4];
    19.         int n = 0;
    20.         while (n < group) {
    21.             int m = 0;
    22.             int words = arr.length;
    23.             int offset = n * gSize;
    24.             for (int i = 0; i < gSize; i++) {
    25.                 int index = offset + i;
    26.                 if (index < length) {
    27.                     m = (m << 8) + bytes[index];
    28.                 } else {
    29.                     if (i == 1) {
    30.                         m = m << 4;
    31.                         words = 2;
    32.                     } else {
    33.                         m = m << 2;
    34.                         words = 3;
    35.                     }
    36.                     break;
    37.                 }
    38.             }
    40.             int r = n << 2;
    41.             for (int i = 4; i > 0; i--) {
    42.                 if (i <= words) {
    43.                     result[r + i - 1] = (byte) CHARACTERS.charAt(m & 0x3f);
    44.                     m = m >> 6;
    45.                 } else {
    46.                     result[r + i - 1] = (byte) '=';
    47.                 }
    48.             }
    50.             n++;
    51.         }
    53.         return new String(result);
    54.     }
    55. }