URLConnections - Java Network Programming - page 220

The query string is built using the add() method. The post() method actually sends
the data to the server by opening a URLConnection to the specified URL, setting its
doOutput field to true , and writing the query string on the output stream. It then returns
the input stream containing the server's response.
The main() method is a simple test for this program that sends the name “Elliotte Rusty
Harold” and the email address [e-mail] to the resource at http://www.cafeau‐
lait.org/books/jnp4/postquery.phtml . This resource is a simple form tester that accepts
any input using either the POST or GET method and returns an HTML page showing the
names and values that were submitted. The data returned is HTML; this example simply
displays the HTML rather than attempting to parse it. It would be easy to extend this
program by adding a user interface that lets you enter the name and email address to
be posted—but because doing that triples the size of the program while showing nothing
more of network programming, it is left as an exercise for the reader. Once you under‐
stand this example, it should be easy to write Java programs that communicate with
other server-side scripts.
Example 7-14. Posting a form
import java.io.* ;
import java.net.* ;
public class FormPoster {
private URL url ;
// from Chapter 5, Example 5-8
private QueryString query = new QueryString ();
public FormPoster ( URL url ) {
if (! url . getProtocol (). toLowerCase (). startsWith ( "http" )) {
throw new IllegalArgumentException (
"Posting only works for http URLs" );
}
this . url = url ;
}
public void add ( String name , String value ) {
query . add ( name , value );
}
public URL getURL () {
return this . url ;
}
public InputStream post () throws IOException {
// open the connection and prepare it to POST
URLConnection uc = url . openConnection ();
uc . setDoOutput ( true );