User's Manual

42 Chapter 7. Developing with WAF
WAF Debugging Setup
In Eclipse, select Run = Debug. In the dialog box, select Remote Java Application and then
click on New. Then enter information for the following tabs:
• Connect Tab
Enter a name for your debug configuration, such as webapp-debug. Select the same project
previously selected as the main project. Enter the host name (localhost should be fine). Use
8000 as your connection port. Also, select Allow termination of remote VM.
• Source Tab
Add all the external JARs under $RESIN_HOME/lib to your source lookup path.
• Common Tab
At the bottom of the dialog box, select Display in favorites menu: Debug.
You are now finished and may close the dialog box.
7.4.5. Eclipse Setup Validation
Your Eclipse setup should now be complete. To test this:
1. Select Run =
External Tools = [Deploy Script].
2. Select Run = Run and pick the WAF configuration. The server’s log output should become
visible in the Console. Wait for the server to finish initializing.
3. Select Run =
Debug and pick the debug configuration. This opens the Debug perspective.
Open a source file, set a breakpoint, and request a page from the server.
If everything is setup correctly, you can now develop with Eclipse and use it to step through your
WAF code.
7.5. Using logging for debugging
When code breaks, there are two ways to figure out what went wrong: launch a debugger and step
through the program, or add logging statements to see what is going on. In its crudest form, logging
means adding a few System.err.println() calls here and there. What are the benefits of logging
over using a debugger?
The Practice of Programming by Brian W. Kernighan and Rob Pike
As a personal choice, we tend not to use debuggers beyond getting a stack trace or the value of a variable
or two. One reason is that it is easy to get lost in details of complicated data structures and control flow;
we find stepping through a program less productive than thinking harder and adding output statements and
self-checking code at critical places. Clicking over statements takes longer than scanning the output of
judiciously-placed displays. It takes less time to decide where to put print statements than to single-step to
the critical section of code, even assuming we know where that is. More important, debugging statements
stay with the program; debugger sessions are transient.
Another important use of logging is to provide an audit trail: who did what and when. The predominant
pattern in WAF is to write such auditing information to the database rather than the filesystem. The
logging framework in WAF is intended to be used primarily for troubleshooting and debugging.