（转帖）重写BASE64Encoder

public class BASE64Encoder {
 6 
 7     private static char[] codec_table = { 'A', 'B', 'C', 'D', 'E', 'F', 'G',
 8             'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
 9             'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
10             'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
11             'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6',
12             '7', '8', '9', '+', '/' };
13 
14     public BASE64Encoder() {
15 
16     }
17 
18     public String encode(byte[] a) {
19         int totalBits = a.length * 8;
20         int nn = totalBits % 6;
21         int curPos = 0;// process bits
22         StringBuffer toReturn = new StringBuffer();
23         while (curPos < totalBits) {
24             int bytePos = curPos / 8;
25             switch (curPos % 8) {
26             case 0:
27                 toReturn.append(codec_table[(a[bytePos] & 0xfc) >> 2]);
28                 break;
29             case 2:
30 
31                 toReturn.append(codec_table[(a[bytePos] & 0x3f)]);
32                 break;
33             case 4:
34                 if (bytePos == a.length - 1) {
35                     toReturn
36                             .append(codec_table[((a[bytePos] & 0x0f) << 2) & 0x3f]);
37                 } else {
38                     int pos = (((a[bytePos] & 0x0f) << 2) | ((a[bytePos + 1] & 0xc0) >> 6)) & 0x3f;
39                     toReturn.append(codec_table[pos]);
40                 }
41                 break;
42             case 6:
43                 if (bytePos == a.length - 1) {
44                     toReturn
45                             .append(codec_table[((a[bytePos] & 0x03) << 4) & 0x3f]);
46                 } else {
47                     int pos = (((a[bytePos] & 0x03) << 4) | ((a[bytePos + 1] & 0xf0) >> 4)) & 0x3f;
48                     toReturn.append(codec_table[pos]);
49                 }
50                 break;
51             default:
52                 //never hanppen
53                 break;
54             }
55             curPos+=6;
56         }
57         if(nn==2)
58         {
59             toReturn.append("==");
60         }
61         else if(nn==4)
62         {
63             toReturn.append("=");
64         }
65         return toReturn.toString();
66 
67     }
68 
69 }

 

这样运行一个测试程序

1 public static void main(String[] args) throws Exception {
 2         
 3 
 4         BASE64Encoder encoder=new BASE64Encoder();
 5         sun.misc.BASE64Encoder sunEncoder=new sun.misc.BASE64Encoder();
 6         byte[] testBytes=new byte[1024*1024*2];
 7         long start=System.currentTimeMillis();
 8         for(int i=0;i<10;i++)
 9         {
10             sunEncoder.encode(testBytes);
11         }
12         
13         System.out.println("[sun encoder]use time :"+(System.currentTimeMillis()-start));
14         start=System.currentTimeMillis();
15         for(int i=0;i<10;i++)
16         {
17             encoder.encode(testBytes);
18         }
19         
20         System.out.println("[our encoder]use time :"+(System.currentTimeMillis()-start));
21 
22     }

 出来的结果是：
[sun encoder]use time :4844
[our encoder]use time :2609
差不多慢一倍。