Java Reference
In-Depth Information
Here's the response from the server:
%
java -classpath .:jnp4e.jar FormPoster
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Query Results</title>
</head>
<body>
<h1>Query Results</h1>
<p>You submitted the following name/value pairs:</p>
<ul>
<li>name = Elliotte Rusty Harold</li>
<li>email = elharo@ibiblio.org
</li>
</ul>
<hr />
Last Modified May 10, 2013
</body>
</html>
The
main()
method tries to read the first command-line argument from
args[0]
. The
argument is optional; if there is an argument, it is assumed to be a URL that can be
POSTed to. If there are no arguments,
main()
initializes
url
with a default URL,
http://
www.cafeaulait.org/books/jnp4/postquery.phtml
.
main()
then constructs a
FormPost
er
object. Two name-value pairs are added to this
FormPoster
object. Next, the
post()
method is invoked and its response read and printed on
System.out
.
The
post()
method is the heart of the class. It first opens a connection to the URL stored
in the
url
field. It sets the
doOutput
field of this connection to
true
because this
URL
Connection
needs to send output and chains the
OutputStream
for this URL to an ASCII
OutputStreamWriter
that sends the data, then flushes and closes the stream.
Do not
forget to close the stream!
If the stream isn't closed, no data will be sent. Finally, the
URLConnection
's
InputStream
is returned.
To summarize, posting data to a form requires these steps:
1. Decide what name-value pairs you'll send to the server-side program.
2. Write the server-side program that will accept and process the request. If it doesn't
use any custom data encoding, you can test this program using a regular HTML
form and a web browser.
3. Create a query string in your Java program. The string should look like this:
name1=value1&name2=value2&name3=value3
