SE2840 Web Application Development
Lab 7: Servlet Context and Sessions

Assignment

In this assignment, you will create a form-processing web application  to provide support for multi-threading, storing data in the Servlet Context, storing data in multiple user Sessions, and error handling.

Details

Create a new Dynamic Web Application for the Tomcat6 runtime in J2EE Eclipse named <yourname>-lab7.

Thus, when your are finished, your application will consist of one servlet (BlogEntryServlet.java), an html page (blog.html), two jsp pages (BlogView.jsp and Error.jsp), and a ServletContext/HTTPSession Listener (BlogListener.java). These are described below.

bulletCreate a blog.html form by modifying the lab6.html form from the previous lab assignment to include a subject input field in addition to the message input field and hidden date fields. Modify your application's Deployment Descriptor (web.xml) such that the blog.html form is the default webpage that is displayed when you enter the url http://localhost:8080/<yourname>-lab7/ into the address bar of a browser:

      

bulletWhen the form is submitted, it should invoke a BlogEntryServlet (modify the FormProcessorServlet.java servlet demonstrated in lecture and available on the course website), which should retrieve the Session and append the information entered into an session-based List<BlogEntry> data structure (base your BlogEntry class on the PhonebookEntry class available on the course website). The data structure will be session-specific, and contain only those BlogEntry elements entered for that specific session.

NOTE: Be sure to modify your application to appropriately protect any data that is not thread-safe, since it can possibly be executing multiple requests simultaneously!
 
bulletAfter adding the form data to the session-based data structure, your BlogEntryServlet servlet should  REDIRECT the client browser to a BlogView.jsp page, where the blogs submitted to-date can be viewed, along with the current session id and the current number of active sessions. Use the application and session implicit variables within the jsp to retrieve the blog entries for the current session, the current session id and current number of active sessions (do not use request parameters).

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Use a 2nd browser to simulate another user submitting blog entries, thereby creating a 2nd session (note: using a 2nd tab in the same browser does not create an additional session):


 
bulletCreate a BlogListener.java class that implements both the ServletContextListener and HttpSessionListener interfaces. You will use this class to create both the single Servlet Context as well as multiple Sessions.
 
bulletin the contextInitialized method, initialize a activeSessions integer variable that counts the number of active sessions to zero, and add that value as an "session count" attribute of the Servlet Context.
 
bulletleave the contextDestroyed method empty.
 
bulletin the sessionCreated method, increment the activeSessions variable, and set that value as the "session count" attribute of the Servlet Context. Create a new ArrayList<BlogEntry> object and add it to the Session as a "blog" attribute. Thus, whenever a new session is created, the "session count" attribute of the Servlet Context is incremented by 1.
 
bulletin the sessionDestroyed method, decrement the activeSessions variable, and set that value as the "session count" attribute of the Servlet Context. Thus, whenever a session is destroyed, the "session count" attribute of the Servlet Context is decremented by 1.
 
bulletYou must add both client-side and server-side validation to your app. On the client-side, using jQuery or plain JavaScript, validate the form input elements so that the form is submitted only if all input elements are not empty, and generates an error message if they are. Of course, you may choose to implement more extensive validation if you choose, which would normally be done in practice.

 

On the server-side, the FormProcessorServlet  validates by checking the submitted content of the input fields: When a user types ??? into either of the text fields, the servlet must add a custom error message to the request object as an attribute and FORWARD the request (via a Request Dispatcher) to a custom error page (Error.jsp) that displays a "user-friendly" error message notifying them of the invalid data entry. This error page should contain a "return to form" hyperlink that, when clicked, leads the user back to the initial form page:

 
 
bulletIn the web.xml file, add a session-config entry that specifies the session-timeout value of 1 (minute). This will result in the automatic destruction of Session data whenever a browser is idle for more than a minute.
 

Submission

When you have finished,

1. Deploy your application to the sapphire server via this Tomcat Web Manager Application link. (Note: you need to either use a VPN or be on-campus to be allowed to access the sapphire server over the network). At the bottom of the Tomcat Web Manager page, you'll see a Deploy section with two forms (Deploy Directory... and WAR file to deploy). Use the War file to deploy form to browse to the location on your local PC filesystem where you created the .war file containing your web application. Note: You create the .war file from within Eclipse by selecting your project and choosing the Export... command from either the main File menu or the context-menu that appears when you right-click on your project. Use the username and password supplied in class in order to login to the Tomcat Web Manager app.

2. zip your Eclipse src and WebContent folders (NOT the entire project folder) and submit it to Blackboard.