URL
The Uniform Resource Locator (URL) locates all of the resources of the Net.
A URL has four components:
- the protocol, separated from the rest of the locator by a colon (:). Common protocols are HTTP, FTP, gopher, and file.
- the host name or IP address, this is delimited on the left by double slashes (//) and on the right by a slash (/) or optionally a colon (:).
- the port number, an optional parameter, delimited on the left from the host name by a colon (:) and on the right by a slash (/). It defaults to port 80, the predefined HTTP port.
- file path.
Java's URL class has several constructors:
URL(String urlSpecifier) throws MalformedURLException- create URL from string
URL(String protocolName, String hostName, int port, String path) throws MalformedURLException- break up the URL into its component parts
URL(String protocolName, String hostName, String path) throws MalformedURLException- break up the URL into its component parts
URL(URL urlObj, String urlSpecifier) throws MalformedURLException- use an existing URL as a reference context and then create a new URL from that context.
To access the actual content, create a URLConnection object from it, using its openConnection( ) method, like this: openConnection( ) has the following general form:
URLConnection openConnection( ) throws IOException
It returns a URLConnection object associated with the invoking URL object.
URL and URLConnection
Outputting the contents of the resource identified via a URL command-line argument
import java.io.InputStream;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
class Main {
public static void main(String[] args) throws Exception {
URL url = new URL("http://google.com");
try (InputStream is = url.openStream()) {
int ch;
while ((ch = is.read()) != -1) {
System.out.print((char) ch);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}