Web App Questions

1. Explain in your own words the meaning of the web "request-response cycle".

   The client sends a request to the server, the server processes the request, the server sends a response, the client figures out what it wants next and sends another request, and the cycle repeats.

2. Explain how servlets facilitate processing of the request-response cycle.

   Servlets to the server-side processing of the cycle. There's a framework that handles receiving the request and sending the response, so you can complete the server side by creating servlets.

3. How do you login to the Tomcat Manager?

   Go to the top level page on the server and click the link.

4. What is the Tomcat Manager used for in the StackStripes application?

   It's not really used inside the application, but the build system uses it to deploy and undeploy the application (and check that it has access to deploy and undeploy).

5. What is the directory and file layout of an installed web application like StackStripes? (This is NOT the same as the directory and file layout of the StackStripes distribution!)

   At the top level, there are JSP pages and the WEB-INF directory. WEB-INF contains web.xml and the directories classes and lib.

6. How do you build a war directory structure in Ant? Where is this accomplished in the StackStripes application?

   The directory structure is built by creating a WEB-INF sub-directory and putting web.xml, classes, and lib. In StackStripes, there's a web directory that already contains the complete structure and the build system copies it to create the directory used to make the war file.

7. How do you install a war directory in a running Tomcat server? What information does the Ant task need to accomplish this?

   GET http://server:port/manager/deploy?path=servpath&war=fullpath where servpath is the path of the installed application within the server (e.g. /stackstripes) and fullpath is the full path of the war directory to install.

8. What is the "Model2" architecture? What are its advantages?

   The design is split into a model, view, and controller. The view is what the user directly interacts with, the model stores the data, and the controller responds to what what the user does to the view by doing things to the model and view.

   The advantages are that it's fairly easy to understand and it separates three types of things that are different, allowing you to do things with just one of them at a time. For example, you can create the view using JSTL, and the controller by writing Java.

9. What are JSP pages? How are they related to servlets?

   JSP pages are web page servlets (or parts of servlets) written in a way that directly includes the static parts of the page.

10. Why is there a delay when retrieving a JSP page for the first time? Where is the Java code for that page stored?

    It has to be converted to Java and compiled. The Java code is stored under a long, complicated path inside the directory where Tomcat is installed.

11. What are JSTL tags? Why are they useful? What is an example JSTL tag from the StackStripes system?

    JSTL is an extension to JSP that adds a lot of tags to take the place of inline Java, making it more of a templating system. For example, the forEach tag is used to iterate through the stack.

12. What are Stripes tags? Why are they useful? What is an example Stripes tag from the StackStripes system?

    Additional tags defined by Stripes. They're useful because they hook in to Stripes. For example the stripes form tag sets up a form that is also connected to an "action bean" by Stripes.

13. What is HttpUnit? How is it different from JUnit? Why is it useful? What is an example use of HttpUnit from the StackStripes system?

    HttpUnit is a library for doing HTTP requests and responses. JUnit is a unit testing framework. HttpUnit is useful because it lets you do HTTP requests and responses from inside the JUnit tests, so that that the tests pass or fail based on the HTTP results. For example, some of our JUnit tests use HttpUnit to retrieve pages and check the contents of the table which displays the stack.

14. What needed to be changed in order to implement the Double It button? What didn't need to be changed? What did you learn about the MVC design pattern from this exercise?

    Added doubleIt to the model, doubleIt to the controller (action bean), and added DoubleItForm to the view (JSP). If your framework isn't very smart, you can find yourself doing everything three times.

15. What are the equivalence classes that need to be tested for the Double It button?

    Empty stack and non-empty stack. You might also divide non-empty stack into one element and many elements.

16. Provide two screen images of your new StackStripes application with the Double It button, one showing the page before and one showing the page after hitting the "Double It" button.

17. What is the singleton design pattern? What is an example of its use in StackStripes? Why is it needed?

    Only one instance of a class can ever be created. The StackStripes model is a singleton because we want all users to share one stack.

18. Some of the StackStripes tests exercise code on the "server side", while others exercise code on the "client" side. Which test classes exercise code on the "server", and which exercise code on the "client"? How does Emma deal with this to create appropriate coverage data?

    TestStackActionBean tests code while it is deployed, and TestStackModel tests code while it is not deployed. Emma records the results in two files and then combines them.

19. Running 'ant -f junit.build.xml' results in the following target invocations: tomcat.check, tomcat.undeploy, compile, war, tomcat.deploy, junit.tool, junit.report, junit. Explain what each of these targets do.

    • tomcat.check checks that the server is up and we can log in
    • tomcat.undeploy undeploys the application
    • compile runs javac
    • war creates a war file
    • tomcat.deploy deploys the application to the server
    • junit.tool runs the JUnit tests
    • junit.report generates a report on the JUnit tests
    • junit depends on junit.tool and junit.report (rather pointless if you ask me -- junit.report could, and probably should, depend on junit.tool and be the default)