Java Network Programming, 4th Edition

Chapter 5. URLs and URIs

In the last chapter, you learned how to address hosts on the Internet via host names and IP addresses. In this chapter, we increase the granularity by addressing resources, any number of which may reside on any given host.

HTML is a hypertext markup language because it includes a way to specify links to other documents identified by URLs. A URL unambiguously identifies the location of a resource on the Internet. A URL is the most common type of URI, or Uniform Resource Identifier. A URI can identify a resource by its network location, as in a URL, or by its name, number, or other characteristics.

The URL class is the simplest way for a Java program to locate and retrieve data from the network. You do not need to worry about the details of the protocol being used, or how to communicate with the server; you simply tell Java the URL and it gets the data for you.

URIs

A Uniform Resource Identifier (URI) is a string of characters in a particular syntax that identifies a resource. The resource identified may be a file on a server; but it may also be an email address, a news message, a book, a person’s name, an Internet host, the current stock price of Oracle, or something else.

A resource is a thing that is identified by a URI. A URI is a string that identifies a resource. Yes, it is exactly that circular. Don’t spend too much time worrying about what a resource is or isn’t, because you’ll never see one anyway. All you ever receive from a server is a representation ...