url-encoded : Java Glossary

You see url-encoding every time you do a Google search e.g.

There are two flavours of urlencoding, one used in URLs, and one used in forms.

URL Encoding

To decode a String, you just feed it to the single-argument URI constructor, then extract the various fields with methods like URI.getPath().

Properly speaking, you should not see bare & in URLs; they should be pre-encoded as &. I wrote a utility called Amper that processes *.html files to make this correction.

Form Encoding

When you use URLEncode.encode you must specify an 8-bit encoding such as UTF-8 or ISO-8859-1. The algorithm first converts to 8-bit characters then encodes. Thus the encoded string depends on the encoding you choose. The encoding is not embedded in the output. You just have to know what it is when an incoming encoding url-encoded string arrives.

java.net.URLEncoder uses the following set of characters to convert 8-bit data into printable characters :a to z, A to Z, 0 to 9, -, ., *, and _. It works like this:

• The alphanumeric characters a to z, A to Z, 0 to 9 remain the same.
• The special characters ., -, *, and _ remain the same.
• The space character is converted into a plus sign +.
• All other 16-bit characters are unsafe and are first converted into one or more bytes using some encoding scheme. Then each byte is represented by the 3-character string %FF, where FF is the two-digit hexadecimal representation of the byte, e. g. $ → %24, % → %25, & → %26, / → %2F, : → %3A, = ⇒ $3D, ? ⇒ %3F. You must URLEncode only once. If you URLEncode something already URLEncoded you will get gibberish.

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