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Question by Connett, D. · Apr 18, 2013 at 12:10 AM ·

Unable to query session attribute for Java Servlets

Hello,
We have a Dev, Perf, and Prod version of an application instrumented, and in the production version we have a particular attribute of interest that I want to create a Business Transaction from.

Unfortunately I get the following when I check the details of the Servlet PurePath: <unable to query value>

This attribute works in all other environments, and this is where usernames are stored.

Here is a screenshot for context:

Thanks!
Dave

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Answer by Andreas G. · Apr 18, 2013 at 02:19 AM

In this case I assume that the session attribute name is wrong. It seems you have specified the class name of the object you expect in the session. However - here you have to specify the name of the session attribute, something like "userBean", "userState", ...
If you dont know what the name of the session attributes are you can specify an "*" (asterisk) in the name column of your sensor properties. This will capture ALL session attributes. This allows you to see which session attributes are available. once you have identified the correct name you can remove the * and use the correct name instead

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avatar image Connett, D. · Apr 18, 2013 at 06:11 PM 0
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Andreas,
I am indeed using the * character and it returns this
<unable to query value>

I am not specifying it by name at all.

-Dave

avatar image Andreas G. ♦ Connett, D. · Apr 18, 2013 at 09:19 PM 0
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Just to clarify. You used the * for the attribute name but not for the "accessor" column in the Sensor Properties?

avatar image Connett, D. Andreas G. ♦ · Apr 18, 2013 at 11:27 PM 0
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That's correct, I used this technique in our performance testing environment and it worked just fine.

I am not sure what could be configured differently between the two environments that would cause this unable to access behavior.

avatar image Andreas G. ♦ Connett, D. · Apr 18, 2013 at 11:33 PM 0
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Please check the agent log files - maybe you find some information there.
Otherwise I suggest opening a support ticket

avatar image Connett, D. Andreas G. ♦ · Apr 19, 2013 at 01:07 AM 0
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Andreas, I checked the agent logs and didn't find anything interesting, I will be opening a ticket and I will reply back with the case# and the results.

Thanks for all your help.

-Dave

avatar image Christian S. Connett, D. · Apr 19, 2013 at 05:01 PM 0
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hi Dave,

this message is returned when there was an exception thrown when calling this attribute's toString() method. unfortunately we currently do not log information about the exception details on any log level.

so i guess there's something special about this environment or the data in this attribute.
however, i have to say i'm a little sceptical about toString() implementations which may throw exceptions ...

hope this helps,
Christian

avatar image Rick B. Christian S. · Apr 19, 2013 at 05:30 PM 0
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Would dynaTrace catch this exception?

avatar image Christian S. Rick B. · Apr 19, 2013 at 09:18 PM 0
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no, because it's an exception which originates from dynaTrace code itself.
dynaTrace only captures exceptions which originate from application code.

there is an agent debug flag which captures all exceptions and logs them to the agent log. however, this will potentially result in a lot of log spam and the desired exception may not be found easily.

anyway, if there's problems finding the toString() issue here, let me know and i'll give you instructions on how to set this debug flag.

avatar image Connett, D. Christian S. · Apr 19, 2013 at 11:19 PM 0
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I see, so the session state could either be encrypted, or our code could actually be disallowed from calling the two string method in this section of the code?

Sounds like I may need to talk to the application engineers (I have already talked to the operators, but it looks like elevation is necessary).

Thanks Christian.

avatar image Andreas G. ♦ Connett, D. · Apr 20, 2013 at 11:25 AM 0
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As Christian said. The problem lies in the ToString() method that we call in order to capture this value. Best is to talk to the developers and ask them why the ToString() method cant be called on its own - why it might thrown an exception

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