Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

17.4 A Query Viewer That Uses Object Serialization and HTTP Tunneling

443

2. Create an 

ObjectOutputStream

.

ObjectOutputStream out = 

new ObjectOutputStream(response.getOutputStream());

3. Write the data structure by using 

writeObject

. Most 

built in data structures can be sent this way. Classes you write, 

however, must implement the 

Serializable

 interface. This is 

a simple requirement, however, since 

Serializable

 defines no 

methods. Simply declare that your class implements it.

SomeClass value = new SomeClass(...);

out.writeObject(value);

4. Flush the stream to be sure all content has been sent to 

the client.

out.flush();

The following section gives an example of this approach.

17.4 A Query Viewer That Uses 

Object Serialization and 

HTTP Tunneling

Many people are curious about what types of queries are sent to the major

search engines. This is partly idle curiosity ( Is it really true that 64 percent of

the queries at AltaVista are from employers looking for programmers that

know Java technology? ) and partly so that HTML authors can arrange their

page content to fit the types of queries normally submitted, hoping to

improve their site's ranking with the search engines.

This section presents an applet/servlet combination that displays the ficti 

tious 

super search engine.com

   live,  continually updating sample que 

ries to visitors that load their query viewer page. Listing 17.4 shows the main

applet, which makes use of an auxiliary class (Listing 17.5) to retrieve the

queries in a background thread. Once the user initiates the process, the

applet places a sample query in a scrolling text area every half second, as

shown in Figure 17 3. Finally, Listing 17.6 shows the servlet that generates

the queries on the server. It generates a random sampling of actual recent

user queries and sends 50 of them to the client for each request.

If you download the applet and servlet source code from

http://www.coreservlets.com/

 and try this application yourself, be

aware that it will only work when you load the top level HTML page by using

Home page for this book: www.coreservlets.com; Home page for sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.