Lab 7a) debug a web application

V4.1
Instructor Exercises Guide

EXempty Exercise 8. Debug a Web Application

Estimated time
00:45

What this exercise is about
In this exercise, you debug the Web application running in the
integrated test environment. IBM Rational Application Developer (V7
and later) includes an integrated testing and debugging environment
that can be used to debug J2EE applications.

What you should be able to do
At the end of the exercise, you will be able to:
• Set up the Test Environment for debugging
• Debug the application in Rational Application Developer

Introduction
The J2EE application that is debugged in this exercise is the library
book renewal application. It is composed of a Web application with an
associated Java utility module. Before the application can be
debugged, the server needs to be started in debug mode.

Requirements
This exercise requires that the library Web project be implemented
(Labs 1-4) and the library database installed (Lab 1).
If the earlier labs were not completed, import the
<LAB_FILES>DatabasesolutionDatabaseSolution.zip file.
The library database needs to be re-installed, but this will be done as
part of this exercise.

© Copyright IBM Corp. 2004, 2007 Exercise 8. Debug a Web Application 8-1
Course materials may not be reproduced in whole or in part
without the prior written permission of IBM.


Instructor exercise overview
In this exercise students will discover an error into the library enterprise application, and will
use the debugging features of IBM Rational Application Developer to find the source of the
error.

Students discover that renewals are being processed even if no renewal period was
requested. This is caused by the renewRequested variable keeping a value of true once it
has been set. The solution is to add a line of code to reset the variable to false as soon as
the request has been processed.

Students reset the LIBRARY Apache Derby database to its initial state. They then run the
application in order to discover the problem. The server is restarted in debug mode,
breakpoints are added, and the students uses the Step Over, Step Into and Step Return
options to view the execution.

Once the problem has been fixed by adding the line of code, the Step-by-Step debug mode
is used to check that the solution works.

8-2 Developing Web Applications © Copyright IBM Corp. 2004, 2007

V4.1

EXempty Exercise instructions
Preface
Open the workspace and if necessary import the required projects (they will already be
there if you are continuing from the previous lab).
The following reference in the exercise instructions represents the directory location in your
workstation:
• <LAB_FILES>: C:LabFiles70



8.1. Prepare the Workspace
The workspace used in the previous lab (Connecting to a Database) should be used as the
starting point for this lab.
If you skipped labs 1, 3 or 4, perform follow the instructions:
__ 1. Start Rational Application Developer.
__ a. In the Workspace Launcher dialog, specify <LAB_FILES>workspace as the
new workspace directory.
__ b. Click OK to open the workspace.
__ c. Import the <LAB_FILES>DatasolutionDatabaseSolution.zip file. If you need
assistance, refer to the instructions in the Appendix, Install the Library
Application in a New Workspace.


V4.1

EXempty 8.2. Reset the Database to Its Default Values
__ 2. Ensure that the Server is stopped, because the Derby database can only serve one
client. When the server is running, the data source is the client, so no other program
can access the database.
__ a. Open the Servers view by selecting Window Show View Servers.
__ b. In the Servers view, make sure that the WebSphere Application Server V6.1
status is Stopped. If the status is Started, right-click the server and select Stop
to stop the server.

__ 3. Run SetUpLibraryDatabase.java.
__ a. In the Project Explorer view, expand LibraryDatabaseSetup driver.
__ b. Right-click SetUpLibraryDatabase.java and select Run As Java
Application.



__ c. The result should be displayed in the Console view.

__ d. The message indicates that the library database has successfully reverted to its
original values.


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EXempty 8.3. Discover the Problem with Consecutive Check Outs
__ 4. Search for the Patron with e-mail dv@bogus.ibm.com.
__ a. In the Project Explorer, expand LibraryWeb WebContent.
__ b. Right click search.jsp and select Run As Run on Server.
__ c. Once the server has started and the search page is loaded in the Web browser,
enter dv@bogus.ibm.com as the Search Phrase and select E-mail as the
Criteria.

__ d. Click Search.
__ 5. Perform consecutive renewal for a different set of items.
__ a. In the search result page, take note of the due date for the items, then select the
first and second check box.

__ b. Click Renew.



Note

Results may vary, based upon the date the database was last refreshed and the date when
Renew is clicked.
This applies to all subsequent results displayed in this lab.

__ c. The first two items are updated with Renewal Status, and the Due Date for the
second book has been extended.
Select the third check box, leaving the first two items unchecked.

__ d. Click Renew again.
__ e. Notice this time, even though the second item was not selected for Renewal, the
minute recorded for the transaction time has been extended again. As well, the
first item still shows the Maximum number of renewals exceeded message when
it was not requested for renewal.

__ f. This time leave all the check boxes cleared, and click Renew twice. The
following screen appears. Notice the second item is declared to exceed the


V4.1

EXempty maximum number of renewals even though it was never selected for renewal
after the first trial.

__ g. Clearly, submitting the form several times consecutively produces logical errors
in the program. You will now debug this application to determine the cause of the
error.



8.4. Debug the Application
__ 6. In order to duplicate the scenario, you must reset the database to its default values.
You can do so by following the instructions outlined in Section 7.2.
__ 7. Restart the WebSphere Application Server in debug mode.
__ a. Open the Servers view.
__ b. Right-click the WebSphere Application Server V6.1 entry and select Debug if the
server is stopped or Restart Debug if the server is already running.
__ c. When the server has restarted, you will notice the status of the server now
indicates that the server is running in debug mode.

__ 8. Since the logic error occurs when renewing the items, the error is likely to be in the
RenewItems servlet or in an object called from that servlet. Set breakpoints in the
RenewItems servlet.
__ a. In the Project Explorer view, navigate to LibraryWeb Java Resources: src
com.ibm.library.servlets.
__ b. Double-click RenewItems to open it in the editor.
__ c. The logic in RenewItems is concentrated in the processRequest method. So
the breakpoint should be set inside that method.
Further examining of the method reveals that the first few statements are general
setup statements. They should not cause any problems. The breakpoint should
therefore be placed at the first statement in the try block.
__ d. Type CTRL-L and enter 74 in the Go to Line dialog to reach the following
statement:
Collection loanList =
(Collection)session.getAttribute("itemList");


V4.1

EXempty __ e. Double-click the vertical ruler on the left of the editor, next to line 74 of the code,
to set a breakpoint at this line. A breakpoint marker now appears on the mark
bar.

__ f. A good practice when debugging is to set breakpoints further down in the source
than your original stopping point. This way, when you determine the problem is
not in the section you are currently debugging, you can click the run button to
skip to the next breakpoint without stopping. Scroll down to line 91 (you can use
CTRL-L) and place a breakpoint beside the following statement:
context.getRequestDispatcher("/listitems.jsp").forward(req,
resp);

__ 9. Debug the Library application on the server.
__ a. In the Project Explorer view, expand LibraryWeb WebContent.
__ b. Right-click search.jsp and select Debug As Debug on Server from the
pop-up menu.



__ c. Once the search page shows up in the browser, enter dv@bogus.ibm.com as
the Search Phrase and select E-mail as the Criteria. Click Search.

__ d. The item list page now shows up. Select the first and second item, and click
Renew.

__ e. When asked to switch to the Debug perspective, click Yes.
__ f. The RenewItems servlet is triggered and the first breakpoint is hit. Click the
RenewItems.java tab and scroll to line 74, the breakpoint line is highlighted.


V4.1

EXempty __ g. You know the renewal process is fine the first time, so you can skip over to the
next breakpoint by clicking the Resume button in the Debug view.

__ h. With the current execution halted on the context.getRequestDispatcher
statement, you can examine the variables resulting from the previous
statements.
__ i. In the Variables view, expand loanList elementData [0], and note the
renewAccomplished, renewMessage, and renewRequested variables.
Those are the ones of interest to this debugging session.

__ j. Expand element [1] and [2] in the elementData array and examine their fields.
Notice that the renewRequested variable is set to true, true, false for
the three items in the array.
__ k. Click the Resume button run the servlet to completion.
__ l. Switch to the Web browser, it should now display the Renewal Status for the
first two items.



__ m. Select the third row, and leave the first two rows clear. Click Renew.

__ n. The debugger should take you to the first breakpoint in RenewItems.java again.
__ 10. Use the various Step commands to examine the variables in the servlet. Note that
loanList is not yet declared.
__ a. Click Step Over in the Debug view toolbar to go to the next statement in the
processRequest method.

__ b. Now loanList should appear in the Variables view. Expand it to examine the
items in the list. Notice for elementData[0], the renewRequested value is still
set to true.


V4.1

EXempty
Note

Note that the ids in the previous Variables view, will vary between executions and
workspaces.

__ c. Click the Step Over button to step over the statement String[] renewList
= req.getParameterValues("RENEW_ITEM");.
__ d. Examine the renewList variable in the Variables view. It should just contain
one element, and that element has a value of 4.

__ e. With the execution halted on the markRenewed method, click Step Into in the
Debug view to move the execution to the first line of the markRenewed method.

__ f. In the markRenewed method, highlight the line
if (Integer.valueOf(renewList[i]).intValue() == itemId) {
Right-click it and select Run to Line to move the execution to this particular
statement.

__ g. You can also evaluate the current if statement without stepping over it. Open
the Display view by selecting Window Show View Display. Copy and paste
the if statement Integer.valueOf(renewList[i]).intValue() ==
itemId to the Display view. Highlight the expression in Display view and select
Display from the pop-up menu. The result should be displayed on the next line.
The value false means that the first item does not match the renew list.



__ h. Back in the RenewItems.java editor, highlight the line
copy.setRenewRequested(true);. Right-click it and select Run to Line.
__ i. In the Variables view, expand copy = LoanedCopy to see that its itemId
matches the itemId local variable.

__ j. Click Step Return in the Debug view to return the execution back to the
processRequest method.

__ k. The Debug Current Instruction Pointer should now point to the
patron.renew(loanList); line. This instruction will execute the renew
command on database, so you need to make sure the data passed in are setup
correctly.
__ 11. Change the variable values in a debugging session.
__ a. In the Variables view, expand loanList elementData [0], [1], [2]. Notice that
the renewRequested variable is set to true, true, true for the three


V4.1

EXempty LoanedCopy elements. Since you only requested that the third book be
renewed, the correct values should be false, false, true.

__ b. Right-click the renewRequested variable under elementData [0] and select
Change Value.



__ c. In the Set Value dialog, enter false. Click OK.

__ d. Similarly, right-click elementData [1] renewRequested and select Change
Value. Enter false in the Set Value dialog, and click OK.
__ e. Now the Variables view should have the three renewRequested variables at
false, false, true as desired.
__ f. Click Step Over to execute the patron.renew instruction.
__ g. Back in the Variables view, you should see that elementData[1] has
renewMessage= " ". Meaning this copy did not get renewed
unnecessarily.
__ h. Click the Resume button twice to finish executing the servlet.
__ i. Switch to the Web browser and the following screen should show. This is the
correct behavior for renewing the third item.


V4.1

EXempty 8.5. Fix the Mistake
By setting the renewRequested variable to false for the non-selected LoanedCopy
elements, you corrected the logic error in the debugging session.
To implement this change in the code, you need to reset all the renewRequested
variables to false by default.
__ 12. One way to do this is to add the line copy.setRenewRequested(false); at the
end of the first while loop of the markRenew method. The change should look like
the following.

__ 13. Save the changes.

Note

The new class should be automatically republished by the server.
There is no need to manually restart the server or application.



8.6. Step-by-Step Debugging
__ 14. Perform Step-by-Step debugging.
__ a. Open the Breakpoints view (on the same tab set as the Variables view), and
clear all of the check boxes to temporarily disable the breakpoints.

__ b. Click on the listitems tab to select the Web browser, type
http://localhost:9080/Library/search.jsp in the address bar, press
ENTER.
__ c. In the search page, enter dv@bogus.ibm.com in Search Phrase, select
E-mail, and click Search. The list items page should now be loaded in the
browser.
__ d. In the Web browser, select all three books for renewal, and click Renew.
__ e. In the Debug view, select the root element WebSphere Application Server
v6.1, and click the Enable Step-by-Step Mode icon.

__ f. In the Web browser, leave all of the check boxes clear, and click Renew.


V4.1

EXempty __ g. A Step-by-Step Debug dialog appears asking you whether to step into the
com.ibm.library.servlets.RenewItems.doPost method. Select Step
into, and click OK.

__ h. The execution should now be halted on the processRequest(req, resp);
line of the doPost method.
__ i. Scroll down the page to line 90, session.setAttribute("itemList",
loanList);. Highlight the line and select Run to Line to move the execution
just before the session attribute is set.
__ j. In the Variables view, examine the content of loanlist. The renewMessage
and renewRequested variables should have the values of &nbsp and false.



Having these results means that the previous logical error of submitting empty
check boxes has been fixed.

__ k. Click the Resume button in Debug view to continue execution.
__ 15. Debug a JSP page.


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EXempty __ a. A Step-by-Step Debug dialog appears again, asking whether to step into
com.ibm._jsp._listitems._jspService. Select Step Into and click OK
to step into the JSP page.

__ b. The JSP page listitems.jsp is loaded in the editor. Click Step Over twice to
reach the <jsp:getProperty> tag.
__ c. Notice in the Variables view, a PATRON object becomes available as a result of
the <jsp:useBean> tag.

__ d. Click Resume to continue executing the JSP page.



__ e. Switch to the Web browser, there should be no messages under the Renew
Status column.

__ 16. Stop the Server. In the Servers view, right-click the server and select Stop.

End of exercise


Lab 7a) debug a web application

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