Bug Hunting

1
Bug Hunting

• Obviously, the best approach to reducing bugs is
  to code to a design and perform testing at
  incremental stages.
• However when you dont know what the problem is
  then
• Whenever you come across an error in your web
  application, you need a mental checklist to help
  you track down the problem.

2
Files and Folders

• Your .htm, .jsp and database files should be
  placed in
• At University
• //trentdev/wwwdatajsp/OOSE/studentid/
• At Home
• /tomcat/webapps/ROOT/

3
Files and Folders

• In the commercial world (or with a hosting
  company), these paths should be
• .htm .jsp goes in /tomcat/webapps/ROOT/AppName/
  
• Database depends! Access anywhere. Database
  folder?
• /tomcat/webapps/ROOT/AppName/database/Access.mdb
• SQL or other database server will be separate
  ask host! Use sqlyog etc.
• Beans /tomcat/webapps/ROOT/AppName/WEB-INF/classe
  s

4
Files and Folders

• Your bean .class files should be placed
• At University
• //trentdev/wwwdatajsp/OOSE/studentid/WEB-INF/class
  es
• At Home
• /tomcat/webapps/ROOT/AppName/WEB-INF/classes/

5
HTML Checklist

• Ensure the server is installed correctly and has
  been started.
• Are you using the correct URL (should start with
  http//)
• Are your .htm files appearing ok
• Do any of your HTML forms contain reserved Java
  keywords as names (e.g. not String, int etc.)
• Do any of your HTML forms contain reserved SQL
  keywords (e.g. name, description etc.)
• http//www.xlinesoft.com/asprunnerpro/articles/sq
  l_access_odbc_reserved_keywords.htm

6
JSP Checklist

• Remember that using GET you are restricted to
  1024 chars.
• You should use POST but GET is good for
  debugging.
• Use the error page material from last week!
• If you are getting a syntax error when the page
  loads and the Java error message isnt
  particularly helpful then you could try opening
  the page in Eclipse (www.eclipse.org) which gives
  possible solutions.

7
Java Bean Checklist

• When you develop your bean, first check that you
  can pass data to and from your JSP before doing
  anything else!!!
• This will check the basic setup of the bean.
• Remember that the names you chose for the HTML
  form elements should be mirrored in the bean
  attributes.
• If you dont do this then the mechanism for
  passing data using the general setProperty wont
  work
• ltjspsetProperty name"Guests" property""/gt

8
Java Bean Checklist

• The names for your get and set methods should
  match the attribute names in your bean.
• e.g. private String username
• public String getUsername() return username
• public void setUsername(String username)
  this.username username
• Use the exception handling methods from last
  week!
• Your package name on the University server should
  be whatever you called it in your Java source
  file.

9
Java Bean Checklist

• Assuming you can pass information to and from the
  JSP page and the Bean and the bean compiles then
  do the following
• Copy the code for the method that doesnt work
  from your bean and put it into your JSP where the
  call to the method is made.
• Comment out the call to the bean method.
• Instead of passing the data to your bean via
  setProperty, get the data via getParameter and
  use this data in your new JSP method.
• This circumvents the bean code and lets you check
  the method directly.

10
Java Bean Extra

• If you are using another class (bean or standard
  Java) in your bean code and you are getting
  compilation errors because your bean cannot find
  the other code then
• javac classpath c\tomcat\webapps\ROOT\AppName\WE
  B-INF\classes MyBean.java
• If you use Eclipse then this should handle all of
  this automatically (even without restarting the
  server!)

11
Caching Problems

• Make sure that in your browser, you have turned
  off page caching In IE, Tools?Internet
  Options?Settings
• Then make sure it is set to
• Every visit to the page (not automatic etc.)
• Then delete all of the current browser cache by
  pressing the Delete Files button and selecting to
  delete all offline content, then hit OK.
• Now retry the page in your browser.

12
Caching Problems

• Even the latest version of Tomcat appears to
  occasionally fall foul to the dreaded caching
  bug.
• Typically, your JSP or bean code has an error in
  it.
• You put in a fix for the error and press CTRLF5
  in the browser but you get the same error
  message.
• To ensure that Tomcat is using the latest version
  of your work you can try the following

13
Caching Problems

• You can force Tomcat to recompile your entire
  application by deleting the contents of the
  following folder
• /tomcat/webapps/ROOT/work/
• Only do this after you have shutdown the server
  or some files may not get deleted!
• Do not delete the work folder itself however.

14
Database Problems

• Remember we are using DSN-less connections.
• Your connection object must have the following
  structure
• At University
• Connection conn DriverManager.getConnection("jdb
  codbcDriverMicrosoft Access Driver
  (.mdb)DBQ//trentdev/wwwdatajsp/OOSE/studentid/
  databasefilename")
• At Home
• Connection conn DriverManager.getConnection("jdb
  codbcDriverMicrosoft Access Driver
  (.mdb)DBQC/tomcat/webapps/ROOT/databasefilena
  me")
• OR, you can use the IP address of your machine
  (127.0.1.2 in this example)
• Connection conn DriverManager.getConnection("jdb
  codbcDriverMicrosoft Access Driver
  (.mdb)DBQ//127.0.1.2/databasefilename")

15
Database Problems

• Instead of having to have two versions of your
  connection code (one for Uni and one for home),
  you could do the following
• try
• Connection conn DriverManager.getConnection("jd
  bcodbcDriverMicrosoft Access Driver
  (.mdb)DBQ//trentdev/wwwdatajsp/OOSE/yc1/Guestb
  ook.mdb")
• catch(SQLException sqlex)
• Connection conn DriverManager.getConnection("jd
  bcodbcDriverMicrosoft Access Driver
  (.mdb)DBQC/tomcat/webapps/ROOT/Guestbook.mdb
  ")

16
Database Problems

• Be very careful with your SQL statements!
• Remember that you cannot put a record into a
  database that has the same primary key value as
  another record.
• You only put apostrophes around values that are
  string-based and your database field is expecting
  Text values. E.g.
• INSERT INTO MyTable (4157, Yvan Cartwright,
  LC24)
• Not this if the first field in the table is
  numeric!
• INSERT INTO MyTable (4157, Yvan Cartwright,
  LC24)
• If you have a problem with currency fields, use
  number, set its field size to Decimal and set
  the format to Currency, then set the number of
  decimal places to 2.