URL : Java Glossary

2007-12-16 by Roedy Green ©1996-2008 Canadian Mind Products
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URL

Uniform Resource Locator. The old name for URI. RFC 1738 describes URL formats. RFC 2396 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 java.net.URL has been replaced by java.net.URI.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/msfirewall.jpg.

Non-ASCII URLs

What if you wanted to embed the following URL in your HTML?

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 ç, ç or ç, 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:

+ 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 the URL class : available:

on the web at java.Sun.com
in the JDK 1.6.0_06 or in the older JDK 1.5.0_15 or the even older JDK 1.4.2_17 on your local J: drive.

Sun’s Javadoc on the URI class : available:

on the web at java.Sun.com
in the JDK 1.6.0_06 or in the older JDK 1.5.0_15 or the even older JDK 1.4.2_17 on your local J: drive.

Sun’s tutorial on URL Introductory

firewall
getResource to create URLs
makeashorterlink
protocol handler
SnipURL
TinyURL
URI
url-encoded
URLConnection
URN

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