重写BASE64Encoder

今天发现JDK1.4中的sun.misc.BASE64Encoder有两个问题
1）编码的字节较长时，encode出来的字符窜会在中间插入\n\r
比如
编码"中华人名* 呵呵呵呵呵呵呵呵呵呵呵呵呵中华人名* 呵呵呵呵呵呵呵呵呵呵呵呵呵"
生成的字符窜居然有两行，中间多了回车换行符。
2）效率较差（见后面的比较)

下面是我的实现：
public class BASE64Encoder {

     private static char[] codec_table = { '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', '+', '/' };

     public BASE64Encoder() {     }

     public static String encode(byte[] a) {
         int totalBits = a.length * 8;
         int nn = totalBits % 6;
         int curPos = 0;// process bits
         StringBuffer toReturn = new StringBuffer();
         while (curPos < totalBits) {
             int bytePos = curPos / 8;
             switch (curPos%8) {
             case 0:
                 toReturn.append(codec_table[(a[bytePos]&0xfc)>>2]);
                 break;
             case 2:
                 toReturn.append(codec_table[(a[bytePos]&0x3f)]);
                 break;
             case 4:
                 if (bytePos == a.length - 1) {
                     toReturn.append(codec_table[((a[bytePos]&0x0f)<< 2)&0x3f]);
                 } else {
                     int pos = (((a[bytePos] & 0x0f) << 2) | ((a[bytePos + 1] & 0xc0) >> 6)) & 0x3f;
                     toReturn.append(codec_table[pos]);
                 }
                 break;
             case 6:
                 if (bytePos == a.length - 1) {
                     toReturn.append(codec_table[((a[bytePos] & 0x03) << 4) & 0x3f]);
                 } else {
                     int pos = (((a[bytePos] & 0x03) << 4) | ((a[bytePos + 1] & 0xf0) >> 4))&0x3f;toReturn.append(codec_table[pos]);
                 }
                 break;
             default:
                 //never hanppen
                 break;
             }
             curPos+=6;
         }
         if(nn==2) {
             toReturn.append("==");
         }
         else if(nn==4){
             toReturn.append("=");
         }
         return toReturn.toString();
     }
}

这样运行一个测试程序

public static void main(String[] args) throws Exception {
         BASE64Encoder encoder=new BASE64Encoder();
         sun.misc.BASE64Encoder sunEncoder=new sun.misc.BASE64Encoder();
         byte[] testBytes=new byte[1024*1024*2];
         long start=System.currentTimeMillis();
         for(int i=0;i<10;i++)  {
             sunEncoder.encode(testBytes);
         }
         System.out.println("[sun encoder]use time :"+(System.currentTimeMillis()-start));
         start=System.currentTimeMillis();
         for(int i=0;i<10;i++) {
             encoder.encode(testBytes);
         }
         System.out.println("[our encoder]use time :"+(System.currentTimeMillis()-start));
     }

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