Server-Side Java with Jakarta-Tomcat

Simple ways to build web applications using servlets.
Displaying the Web Log

Now that we have seen how a servlet can be used to enter information into our web log, we will write another servlet to display the latest contents. This servlet will be relatively simple; it will take no parameters and will display the latest contents of the web log (see Listing 4 at ftp://ftp.linuxjournal.com/pub/lj/listings/issue84/).

Our ShowBlog servlet will only have two methods, init (which is identical to the “init” method from AddBlogEntry) and doGet. doGet will retrieve all of the entries in a web log, from the newest to the oldest. It displays each entry as a three-column row in an HTML table, showing the date and time at which it was added, the headline and the text associated with that headline.

Of course, a real web log will do things in a slightly more intelligent way, limiting the number of remarks and arranging them with a better sense of design. But that's easy enough to do once we have retrieved the information from the database in the correct order.

We create our query (inside of a “synchronized” block) and wrap it into a Statement. Notice how we need not use a PreparedStatement because we are not planning to instantiate any variable values into the statement.

We retrieve the results from the query into a ResultSet:

ResultSet rs = statement.executeQuery(query);

A ResultSet allows us to pull results out of the database one row at a time. We can iterate through each row inside of a while loop using the rs.next( ) method. Within each iteration, we can retrieve a column as a String value using the rs.getString( ) method, passing the name of the column as a parameter.

After compiling this servlet and placing it on my system, I was able to add some new web log entries and display them within a matter of minutes.

Conclusion

Servlets are the Java world's equivalent to the Perl world's modules for mod_perl. In many ways, they are actually better as they provide a great deal of power without endangering the web server with potentially risky programs. This month, we saw some simple ways to build web applications using servlets and open-source tools that we can download from the Web. Next month, we will continue our exploration of server-side Java by looking at some simple uses for Java Server Pages, also known as JSPs.

Resources

Reuven M. Lerner owns and manages a small consulting firm specializing in web and internet technologies. As you read this, he should be (finally!) finishing Core Perl, to be published by Prentice-Hall later this year. You can reach him at reuven@lerner.co.il, or at the ATF home page, http://www.lerner.co.il/atf/.

______________________

Comments

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Where is it?

Andy Canfield's picture

servlet.jar is now named servlet-api.jar. Use 'locate' to find it on your particular system.

Webinar
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Webinar
Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix