Base64是一种基于64个可打印字符来表示二进制数据的表示方法。由于2的6次方等于64，所以每6个位元为一个单元，对应某个可打印字符。三个字节有24个位元，对应于4个Base64单元，即3个字节需要用4个可打印字符来表示。它可用来作为电子邮件的传输编码。-Base64 is based on 64 printable characters to represent binary data representation. Since 2 ^ 6 equals 64, so every six bits as a unit, which corresponds to a printable character. Three bytes are 24 bits, corresponding to four Base64 units, or 3 with the four bytes required to represent printable characters. It can be used as an e-mail transfer encoding.