Re: Debugging Servlets

Francess,

Your instructions worked. If anyone else is interested, here is what worked. I 
created a new directory called classes in Tomcat's root (this is where Tomcat 
/lib is). Next I compiled to that directory with both .class and .java.  I then 
deleted the original .jar. Next, I changed my Tomcat startup script to specify 
-Djava.compiler=NONE and also added the /classes directory to the startup 
CLASSPATH.

Once Tomcat started, I ran the strdbgsvr command, located the server job (this 
one was qp0zspwt), and started the distributed debugger. I specified my 
qp0zspwt job and entered the class that I wanted to debug.  Next, I went to the 
offending web page and hit shift-F5. I am still trying to figure out the 
debugger, but this is miles ahead of logging statements.

That's about it, thanks for your help.  I did find that I have no help text for 
the distributed debugger on this system (I installed it via WDT400).  I did 
have help text on my other system where it was installed as part WS Studio 
Advanced.


Thanks,

David Morris  



>>> francess@us.ibm.com 05/04/01 04:34 AM >>>

Hopefully some of this information will help:

1). You don't need to do the javac -g on the 400. It is fine to use the
debuggable code that comes from VAJ, or if the javac -g was done on your
PC.

2). You do need to have the source files (*.java) be in a directory (i.e.
not in the jar file with the classes). The system debugger and the
distributed debugger both have this requirement.  The easiest way is to
have the source be in the same directory as the jar file, but you can also
use the DEBUGSOURCEPATH environment variable to specify the location of the
source if it is not.

3). Neither the system debugger nor the distributed debugger will work if
the class is loaded b a custom classloader (you mention 'Tomcat's
classloader' below).  The class must be loaded by the system class loader
(a.k.a JVM class loader). Generally customer class loader's always defer to
the system class loader to load a class if possible, so if Tomcat has a
mechanism for  specifying a classpath that is passed into the JVM (e.g.
java -classpath ...), you should use that.  That does mean you will have to
stop and restart Tomcat whenever you introduce a debuggable class.
If Tomcat does not have a mechanism for specifying -classpath ... classes,
you could try putting the classes in /QIBM/ProdData/Java400. You would need
to extract the classes from the jar file and make sure they are in the
appropriate package scoped directory structure under
/QIBM/ProdData/jJava400.  This path is always on the classpath for the JVM.

4). Neither the system debugger nor the distributed debugger work if the
JITC (Just-in-time compiler) is being used. In v4r5 and later I believe
this is the default.  To disble the JITC, you need to specify JVM system
property java.compiler=NONE.  If Tomcat does not have a way for you to pass
in -Djava.compiler=NONE when starting the JVM (e.g. java
-Djava.compiler=NONE), you can specify this in the SystemDefault.properties
file at various levels depending on your need and who you want to impact.

5). You do not need to use RUNJVA to start Tomcat in order to debug using
the AS/400 System Debugger. Item 6 and 8 below contain links to more
detailed documentation on this, but basically you use STRSRVJOB and STRDBG
to accomplish debugging of a job that is already running.

6). This link might help:
http://publib.boulder.ibm.com/pubs/html/as400/v4r5/ic2924/info/java/rzaha/debserv.htm
It is a short list of the steps to debug a servlet on the 400.  You can get
to it by going to the v4r5 Information Center then expanding
Programming->Java->AS/400 Development Kit for Java->Debugging->Debug
servlets

7). The IBM Distributed Debugger does contain information on debuggingon
the AS/400 in its help files.

8). Lastly the WebSphere documentation contains information on using both
the system debugger and the IBM Distributed Debugger to debug servlets,
JSPs and EJBs.  You would need to extrapolate to Tomcat on some of the
information, but I think the detailed info on the STRSRVJOB and STRDBG
commands will help you, and the information pertainining to Using the IBM
Distributed Debugger in standalone mode will help.  The starting point for
this documentation is at
http://www-1.ibm.com/servers/eserver/iseries/software/websphere/wsappserver/docs/as400v35std/docs/trb.html

 The two topics you would be interested in are 'Using the IBM DIstributed
Debugger without Object Level Trace' and 'Using the AS/400 System
Debugger'.


Frances Stewart
WebSphere Application Server for iSeries 400
IBM Rochester


"David Morris" <dmorris@plumcreek.com>@midrange.com on 05/03/2001 05:21:17
PM

Please respond to JAVA400-L@midrange.com

Sent by:  owner-java400-l@midrange.com


To:   <JAVA400-L@midrange.com>
cc:
Subject:  Debugging Servlets



Group,

I have been working with some large Jar files trying to work out some bugs.
My debug
process is to add logging statements where necessary and then republish the
results.
This code is only having a problem running on my iSeries and not on any
other platform
that I have deployed it to.  I am using the Enterprise version of VA/Java
and its debugger
works great when running on my PC. I tried the distributed debugger and
can't seem to
get it to work against my deployed Jar files.  I compile and deploy with
debugging enabled.

I am using Tomcat so it is not too much bother to run this interactively.
I have not figured out
how to debug code in a Jar file and removing a single class causes a
problem with
Tomcat's class loader (it always picks up the Jar version).

I have a couple of ideas.  First deploy as java files and then compile on
the AS/400 and
run javac -g.  I am not sure how I start debugging unles I use runjva
against tomcat start.
Is there a way to pick up a class other than the initial class?  Also how
would I compile
my 400 classes with javac (I suspect a simple qshell script, but an example
would help).

The next idea is to figure out the distributed debugger, which I think is
hindered by the same
problems I am seeing with the interactive debugger.

I appreciate any input or ideas.

David Morris



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