Wireless Java

The HTTP Programming Model

HTTP is a request-response application protocol. When programming with Java HTTP libraries, such as the Generic Connection Framework, the parameters of the request must always be set before the request is sent. This allows the entire request, including parameters, to be sent at the same time.

Request Methods

There are two commands to send data from a form on a web page to a CGI script or a servlet hosted by the HTTP server. These commands are GET and POST. Each of these has a different way of sending data to the server.

• For the GET method, the input values are sent as part of the URL in the QUERY_STRING environment variable.

• For the POST method, data is sent as an input stream and its length is saved in the CONTENT_LENGTH environment variable.

The POST method is more secure, and you can send more data using it. As an example, consider the following HTML code for the form shown in Figure 7-3.

Figure 7-3. Form with one field (GET method)

<form action=http://www.somesite.com/cgi-bin/getgrade.cgimethod="GET"> 
Student#: 
<input type="text" name="idnum" size=30>
<input name="RetrieveMarks" value="Retrieve Marks" type="submit"> 
</form>

This form is handled by the script at http://www.somesite.com/cgi-bin/getgrade.cgi. Note that the form uses the GET method to transmit the information. When the user enters a student number, such as 112233, and clicks the Retrieve ...