URLs and URIs - Java Network Programming - page 119

telnet
A connection to a Telnet-based service
urn
A Uniform Resource Name
In addition, Java makes heavy use of nonstandard custom schemes such as rmi , jar ,
jndi , and doc for various purposes.
There is no specific syntax that applies to the scheme-specific parts of all URIs. However,
many have a hierarchical form, like this:
// authority / path ? query
The authority part of the URI names the authority responsible for resolving the rest of
the URI. For instance, the URI http://www.ietf.org/rfc/rfc3986.txt has the scheme http ,
the authority www.ietf.org , and the path /rfc/rfc3986.txt (initial slash included). This
means the server at www.ietf.org is responsible for mapping the path /rfc/rfc3986.txt to
a resource. This URI does not have a query part. The URI http://www.powells.com/cgi-
bin/biblio?inkey=62-1565928709-0 has the scheme http , the authority www.po‐
wells.com , the path /cgi-bin/biblio , and the query inkey=62-1565928709-0 . The URI
urn:isbn:156592870 has the scheme urn but doesn't follow the hierarchical //authority/
path?query form for scheme-specific parts.
Although most current examples of URIs use an Internet host as an authority, future
schemes may not. However, if the authority is an Internet host, optional usernames and
ports may also be provided to make the authority more specific. For example, the URI
ftp://mp3:[e-mail]:33/VanHalen-Jump.mp3 has the au‐
thority mp3:[e-mail]:33 . This authority has the username
mp3 , the password mp3 , the host ci43198-a.ashvil1.nc.home.com , and the port 33 . It has
the scheme ftp and the path /VanHalen-Jump.mp3 . (In most cases, including the pass‐
word in the URI is a big security hole unless, as here, you really do want everyone in
the universe to know the password.)
The path is a string that the authority can use to determine which resource is identified.
Different authorities may interpret the same path to refer to different resources. For
instance, the path /index.html means one thing when the authority is www.landover‐
baptist.org and something very different when the authority is www.churchofsa‐
tan.com . The path may be hierarchical, in which case the individual parts are separated
by forward slashes, and the . and .. operators are used to navigate the hierarchy. These
are derived from the pathname syntax on the Unix operating systems where the Web
and URLs were invented. They conveniently map to a filesystem stored on a Unix web
server. However, there is no guarantee that the components of any particular path ac‐
tually correspond to files or directories on any particular filesystem. For example, in the
URI http://www.amazon.com/exec/obidos/ISBN%3D1565924851/cafeaulaitA/
002-3777605-3043449 , all the pieces of the hierarchy are just used to pull information