URL : Java Glossary

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URL
Uniform Resource Locator. The old name for URI. RFC 4248 describes URL formats. RFC 3986 describes URI formats. java.net.URL has been replaced by java.net.URI. Strictly speaking, every URL is a URI, but not every URI is a URL. URI’s are an extension and refinement of the URL. Yet, as classes, neither is a subclass of the other and they have no common base other than Object. java.net. URI is Java’s second attempt at doin a URL class an they started from scratch.

URLs never automatically armour their parameters, where URIs sometimes do.

If a bug report I got is correct, under some conditions JDK 1.6 URL.openConnection returns null without throwing an IOException.

The term URL can also be an as a verb, as in “Please URL me that picture of the Windows Firewall”, meaning “Please email me the URL of that photograph”, in other words email the text: http://mindprod.com/image/jgloss/msfirewall.jpg.

Non-ASCII URLs

What if you wanted to embed the following URL in your HTML?
<a href="http://en.wikipedia.org/wiki/Façade_pattern">
What do you do about that pesky non-ASCII ç character? HTML 4.01 says URLs should only contain ASCII chars, but if non-ASCII chars appear they should be treated as UTF-8. In theory you should be able to encode it with &ccedil;, &#231; or &#xe7;, but in practice, you can’t count on this working. You must use the URL-Encoded %hh escaping mechanism of the equivalent UTF-8 chars like this:
<a href="http://en.wikipedia.org/wiki/Fa%E7ade_pattern">
+ is converted to %2B and space is converted to +.

URLs always use UTF-8 encoding, no matter what the encoding of the enclosing document.

Learning More

Sun’s Javadoc on URL class : available:
Sun’s Javadoc on URI class : available:
Sun’s tutorial on URL Introductory
firewall
getResource to create URLs
IDN
makeashorterlink
protocol handler
SnipURL
TinyURL
URI
url-encoded
URLConnection
URN
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