I am trying to figure out what is difference between these two ways of Base64 conversions:

First:

String base64EncodedMsg = Base64.getUrlEncoder().encodeToString(messageInBytes);

and

Second:

String base64EncodedMsg = new String(Base64.getEncoder().encode(messageInBytes));

Where messageInBytes is of type byte[]

For a certain value of messageInBytes, values of base64EncodedMsg slightly differ.

With first call I get it as:

1HuW7rb7_l7NC7LwR7cRV2K-rlr7SnGdoEuGntxDKX8=

And with second call I get it as:

1HuW7rb7/l7NC7LwR7cRV2K rlr7SnGdoEuGntxDKX8=

Can someone please explain? Thanks in anticipation.

CodePudding user response：

The standard base-64 alphabet contains the characters and /, which have special meaning in a URL. To deal with this, there's a "URL friendly" variant of base-64, which doesn't use these characters - it uses - and _ instead. This saves things from getting scrambled if you use a base-64 string in a URL.

Your two snippets of code show conversion to "URL friendly base-64" and standard base-64 respectively.

CodePudding user response：

These two methods of Base64 instance are just returning Encoder with different policy of RFC4648 base64 conversion standard.

Just compare:

public static Encoder getEncoder() {
     return Encoder.RFC4648;
}

and:

public static Encoder getUrlEncoder() {
     return Encoder.RFC4648_URLSAFE;
}

Read more here:

• 

  CodePudding user response：

  There are two Base64 alphabets of "digits." Both Base64 use 26 capital letters 26 small letters 10 digits = 62 digits. The normal Base64 adds and /. The URL safe Base64 uses the neutral - and _.

  As a Base64 digit represents 6 bits, 4 digits represent 3 bytes. As padding at the end with =s is done.

  base64EncodedMsg = new String(Base64.getEncoder().encode(messageInBytes));
  

  gives the normal Base64, but contains a non-portable error. The new String(bytes) uses the platform encoding and hence is not portable. As long as the platform encoding is a superset of ASCII it works, but encodings like wide characters (UTF-16) or EBCDIC would corrupt the message.

  Correct is new String(bytes, StandardCharsets.US_ASCII) or simply:

  base64EncodedMsg = Base64.getEncoder().encodeToString(messageInBytes);