如何计算Base64编码字符串的长度？公式验证测试解析

Hey everyone,

I recently looked into calculating the length of Base64-encoded strings and came across this handy formula that matches real-world behavior perfectly:
length = 4 * ceil(n / 3)
(Where n is the number of bytes in your original input string)

To confirm this, I ran several tests using Java's built-in Base64 encoder. Here's what I found:

• 1 character input ("1")
  • Code used: Base64.getEncoder().encodeToString("1".getBytes())
  • Encoded output: MQ== → 4 characters total
• 2 characters input ("12")
  • Code used: Base64.getEncoder().encodeToString("12".getBytes())
  • Encoded output: MTI= → 4 characters total
• 5 characters input ("12345")
  • Code used: Base64.getEncoder().encodeToString("12345".getBytes())
  • Encoded output: MTIzNDU= → 8 characters total
• 8 characters input ("12345678")
  • Code used: Base64.getEncoder().encodeToString("12345678".getBytes())
  • Encoded output: MTIzNDU2Nzg= → 12 characters total

The core logic here is that Base64 converts every 3 input bytes into 4 encoded characters. If the input byte count isn't a multiple of 3, padding characters (=) are added to make the final length a multiple of 4—this is why we use the ceiling of n/3 in the formula to account for partial byte chunks.

内容的提问来源于stack exchange，提问作者gstackoverflow