Java IO.pdf - Nguyen Dang Binh

Chapter 5. Network Streams
Java I/O
From its first days, Java has had the network in mind, more so than any other common
programming language. Java is the first programming language to provide as much support
for network I/O as it does for file I/O, perhaps even more—Java's URL, URLConnection,
Socket, and ServerSocket classes are all fertile sources of streams. The exact type of the
stream used by a network connection is typically hidden inside the undocumented sun classes.
Thus, network I/O relies primarily on the basic InputStream and OutputStream methods,
which you can wrap with any higher-level stream that suits your needs: buffering,
cryptography, compression, or whatever your application requires.
5.1 URLs
The java.net.URL class represents a Uniform Resource Locator like
http://metalab.unc.edu/javafaq/. Each URL unambiguously identifies the location of a
resource on the Internet. The URL class has four constructors. All are declared to throw
MalformedURLException, a subclass of IOException.
public URL(String u) throws MalformedURLException
public URL(String protocol, String host, String file)
throws MalformedURLException
public URL(String protocol, String host, int port, String file)
throws MalformedURLException
public URL(URL context, String u) throws MalformedURLException
A MalformedURLException is thrown if the constructor's arguments do not specify a valid
URL. Often this means a particular Java implementation does not have the right protocol
handler installed. Thus, given a complete absolute URL like
http://www.poly.edu/schedule/fall97/bgrad.html#cs, you construct a URL object like this:
URL u = null;
try {
u = new URL("http://www.poly.edu/schedule/fall97/bgrad.html#cs");
}
catch (MalformedURLException e) { }
You can also construct the URL object by passing its pieces to the constructor:
URL u = null;
try {
u = new URL("http", "www.poly.edu", "/schedule/fall97/bgrad.html#cs");
}
catch (MalformedURLException e) { }
You don't normally need to specify a port for a URL; most protocols have default ports. For
instance, the HTTP port is 80. Sometimes the port used does change, and in that case you can
use the third constructor:
URL u = null;
try {
u = new URL("http", "www.poly.edu", 80,"/schedule/fall97/bgrad.html#cs");
}
catch (MalformedURLException e) { }
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