Base64编码的思想是是采用64个基本的ASCII码字符对数据进行重新编码。它将需要编码的数据拆分成字节数组。以3个字节为一组。按顺序排列24 位数据，再把这24位数据分成4组，即每组6位。再在每组的的最高位前补两个0凑足一个字节。这样就把一个3字节为一组的数据重新编码成了4个字节。当所要编码的数据的字节数不是3的整倍数，也就是说在分组时最后一组不够3个字节。这时在最后一组填充1到2个0字节。并在最后编码完成后在结尾添加1到2个 “=”。

-The idea of ​ ​ the Base64 encoding 64 basic ASCII character data re-encoding. It will need the encoded data is split into an array of bytes. For a group of three bytes. Order 24, then 24 data divided into four groups, namely, six in each group. Before the highest bit of each to fill two 0 to kick in a byte. So put a 3-byte data for a group of re-encoded into four bytes. When the number of bytes of data to be encoded is not an integer multiples, that is in the packet when the last group of less than 3 bytes. Then fill in the final set 1-2 0 bytes. And at the end after the completion of the last coding to add 1-2 " =" .