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Lab 5: Servlet Configuration and Session

Page Contents:

Goals

At the completion of this lab, you should be able to

Set up

Adding init and destroy Methods (37 pts)

SurveyServlet is not implemented very efficiently. The results file has to be read and written every time a vote is cast, i.e., every time a request comes in. We don't want that overhead because we expect this survey to be taken a lot! (Not really but...)

Add init and destroy methods to SurveyServlet. init will read the file and initialize the votes. destroy will write the votes out to the file. More detailed instructions follow:

  1. First, recall that you can use the "Refactor" and "Source" menus of Eclipse to quickly do trivial tasks.
  2. In the SurveyServlet.java editor pane, right-click, select "Source", and then "Override/Implement Methods".
  3. Under the GenericServlet class, select init and destroy, select where to put them (I put them below the constructor), and then click "OK". These method stubs will be automatically generated for you.
  4. Move the variables surveyData, votesForAnimals, and totalVotes so that they are instance variables for the class rather than temporary variables for the doGet method.
  5. Move the code that reads in the file into the init method. Keep the call to super.init() first. You will have to handle some compiler errors appropriately. Handle errors in a thoughtful way--not like you're just telling Eclipse to fix them all and not thinking about the cleanliness of the resulting code.
  6. Move the code that writes the file into the destroy method. Make the call to super.destroy() last. You will have to handle some compiler errors appropriately. Handle errors in a thoughtful way--not like you're just telling Eclipse to fix them all and not thinking about the cleanliness of the resulting code.
  7. Stop and restart your server in the Server view.
  8. Test your servlet several times.
  9. Stop and restart your server.
  10. Test again. It's using the updated data, right? Good!

Web Application Structure and Deployment

build Directory

Within a terminal (not within Eclipse), look at the contents of the build directory inside of your First project. You should see the .class files for each of your servlets, within the classes/servlets (or whatever package name you used). The build directory and the contents of the WebContent directory (or the src/main/webapp directory) are what are deployed on the server.

Eclipse Web Tools Platform (WTP)

Typically, web applications are put in Tomcat's webapps directory to be deployed. The Eclipse WTP handles putting your files in an appropriate location.

Within a terminal, if you go into your workspace, and then from there go into .metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/Lab5, you should see your .html and .css files as well as a META-INF and WEB-INF directory. Note that you won't see the .metadata directory because it is hidden because it starts with a .. To view all the files, use the command-line option -a, e.g.,
ls -a

Go into the WEB-INF directory. You should see a classes directory and a lib directory and, perhaps, a web.xml file. The classes directory contains the servlets you wrote. The lib directory contains any jar files that you imported for your applications (beyond the standard Java EE classes).

Configuration (25 pts)

Sometimes, you need to configure your servlets. For example, you want to tell the servlet the location of a file or the parameters to a database or the email address of the administrator.

URL Mapping

  1. Modify the LoginServlet such that its @WebServlet annotation for the URL mapping is /login instead of /LoginServlet
  2. Modify the login form to send requests (its action) to login instead of LoginServlet
  3. Test that the login functionality still works as expected.

Init Parameters

  1. Modify the SurveyServlet to include an init parameter. The init parameter's name is surveyFile and the value is survey.dat.

    You can modify the web.xml file or add the annotations to SurveyServlet. To see examples of annotations, look at the slides or use Eclipse to create a new servlet and generate an example annotation for you. To create a web.xml file, you can right-click on the project, go to JavaEE Tools, and then select Generate Deployment Descriptor Stub

    2. You modify web.xml from the Source or the Design view, which ever you are more comfortable with. In Design view, you can right click on the SurveyServlet's servlet element and select "Add Child" and add "init-param". If you expand init-param, you'll see the two elements that you need to fill in. Click on "Source" view to see the result. I want you to be very comfortable with XML files.

  2. Modify SurveyServlet's init method to access the init parameter and refactor your code to use it. (Look at the methods that SurveyServlet inherits from HttpServlet).
  3. Stop and restart the server.
  4. Test that the code still works correctly.
  5. Stop the server. Modify the parameter so that the SurveyServlet's init parameter has a different file name, such as survey2.dat.
  6. Restart the server and test your code. You should not get the data you had before: it should be all 0s, except for whatever you just voted for.

Using Sessions and Session Variables (23 pts)

Modify your Login servlet so that, if the user's name and password are correct, it starts a new HttpSession and stores an attribute with name authenticated and value a Boolean object that has a true value. (Note that this must be a Boolean object and not a boolean. Why? What is the difference between boolean and Boolean?)

Also set your session's maximum inactive interval to 60 seconds.

To test that your servlet is working correctly:

  1. Copy this form and this image in your WebContent (or src/main/webapp) directory. (In the browser, you can say to "Save as" and put them in the appropriate location.)
  2. Update your index.html file to have a link to your authentication test.
  3. Create a new servlet in the servlets package named AuthenticatedTest
  4. Copy this code into the doGet method of the servlet you just created (AuthenticatedTest). Look at the code to understand what it is supposed to do. Handle compiler errors appropriately.
  5. Restart your server.
  6. Try clicking the button of the authenticate test form. You should see a message that says that you're not authenticated.
  7. Login, using your login form copied from last lab.
  8. Try clicking the button of the authenticate test form again. You should now see a message that you are authenticated.
  9. Wait 60 seconds and test the authenticate test form again. You should no longer be authenticated because the session expired.

Submission

Create a .war file from your Lab5 project named--you guessed it--Lab5.war and copy it into your git repository from last lab. Make sure to include the source code.

Grading (90 pts)

Due tonight at 11:59 p.m.