What’s the difference between URL Encoding and Form URL Encoding?

URL Encoding

Sometimes refered to as Percent Encoding, this scheme is intended to encode non-ASCII characters consistently in URLs. For example, characters like # have special meaning in a URL and would need to be converted to avoid problems. The scheme is recognisable by the replacement of characters with a percentage value. For example, the space character gets replaced by %20.

In Java, you can create an encoded URL using

new java.net.URI("http", "baddotrobot.com", "/cheese sandwich").toURL();

which in this case produces

http:baddotrobot.com#/cheese%20sandwich

Form URL Encoding

Refered to by the application/x-www-form-urlencoded mime-type. This scheme was based on an early version of URL Encoding but at some point diverged. For example, the space character gets replaced by the + rather than %20. It’s typically used for encoding POST message content by HTML forms.

For example, a HTML form with name and address would send over the following.

POST http://baddotrobot.com/ HTTP/1.1
Content-Type: application/x-www-form-urlencoded

name=bad.robot&address=the+land+of+make+believe

Use the unhelpfully named class URLEncoder in Java

java.net.URLEncoder.encode(value, "UTF-8");

Base64 Encoding

Another one to be aware of, this is a basic encoding used by various protocols related to HTTP. For example, basic authentication is supported by adding a Authorization header with base 64 encoded username and password; you’d do something like the following.

new header("Authorization", "Basic " + new sun.misc.Base64Encoder().encode("username:password".getBytes()));

Which, for example, could be used to send the following HTTP message

GET /login HTTP/1.1
Authorization: Basic dXNlcm5hbWU6cGFzc3dvcmQ=