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17.3 Sending Data with GET and Processing the Results Directly

441

Reading Serialized Data Structures

The approach shown in the previous subsection makes good sense when

your applet is talking to an arbitrary server side program or reading the

content of static Web pages. However, when an applet talks to a servlet,

you can do even better. Rather than sending binary or ASCII data, the

servlet can transmit arbitrary data structures by using the Java serialization

mechanism. The applet can read this data in a single step by using 

readOb 

ject

; no long and tedious parsing is required. The steps required to imple 

ment HTTP tunneling are summarized below. Again, note that the

statements need to be enclosed within a 

try

/

catch

 block in your actual

applet.

The Client Side

An applet needs to perform the following seven steps to read serialized data

structures sent by a servlet. Only Steps 5 and 6 differ from what is required to

read ASCII data. These steps are slightly simplified by the omission of the

try

/

catch

 blocks.

1. Create a 

URL

 object referring to the applet's home host. 

As before, since the URL must refer to the host from which the 

applet was loaded, it makes the most sense to specify a URL 

suffix and construct the rest of the URL automatically.

URL currentPage = getCodeBase();

String protocol = currentPage.getProtocol();

String host = currentPage.getHost();

int port = currentPage.getPort();

String urlSuffix = "/servlet/SomeServlet";

URL dataURL = new URL(protocol, host, port, urlSuffix);

2. Create a 

URLConnection

  object. The 

openConnection

method of 

URL

 returns a 

URLConnection

 object. This object 

will be used to obtain streams with which to communicate. 

URLConnection connection = dataURL.openConnection();

3. Instruct the browser not to cache the URL data. The first 

thing you do with the 

URLConnection

 object is to specify that 

the browser not cache it. This guarantees that you get a fresh 

result each time. 

connection.setUseCaches(false); 

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