Java Examples in a Nutshell, 3rd Edition

Downloading the Contents of a URL

Example 5-1 shows how you can download the network resource referred to by a URL using the URL class. This class serves mainly to represent and parse URLs but also has several important methods for downloading URLs. The most high-level of these methods is getContent( ), which downloads the content of a URL, parses it, and returns the parsed object. This method relies on special content handlers having been installed to perform the parsing. By default, the Java SDK has content handlers for plain text and for several common image formats. When you call the getContent( ) method of a URL object that refers to a plain text or GIF or JPEG image file, the method returns a String or Image object. More commonly, when getContent( ) doesn’t know how to handle the data type, it simply returns an InputStream so that you can read and parse the data yourself.

Example 5-1 doesn’t use the getContent( ) method. Instead, it calls openStream( ) to return an InputStream from which the contents of the URL can be downloaded. This InputStream is connected, through the network, to the remote resource named by the URL, but the URL class hides all the details of setting up this connection. (In fact, the connection is set up by a protocol handler class; the Java SDK has default handlers for the most common network protocols, including http:, ftp:, mailto: and file:.)

Example 5-1 is a simple standalone program that downloads the contents of a specified URL and saves ...