Server-Side Java with Jakarta-Tomcat
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.
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.
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems
Join editor Bill Childers and Bit9's Paul Riegle on April 27 at 12pm Central to learn how to keep your Linux systems secure.
Free to Linux Journal readers.Register Now!
- Python Scripts as a Replacement for Bash Utility Scripts
- Cluetrain at Fifteen
- Considering Legacy UNIX/Linux Issues
- [<Megashare>] Watch Mrs Brown's Boys Movie Online Full Movie HD 2014
- Memory Ordering in Modern Microprocessors, Part I
- Getting Good Vibrations with Linux
- Putlocker!! Watch Begin Again Online 2014 Streaming Full Movie
- New Products
- RSS Feeds
- Security Hardening with Ansible