ClassNotFoundException Applet

[Sanket Gupte]

Hello

I am having this problem for a while now, and have been trying hard to ignore all the whining, and complains and hate mail that I am getting from my people, coz I haven't been able to fix it yet. But it's high time now.

So somehow none of the Applets are working. Every time someone tries to run an applet, (Image Viewer, Download applet, Upload Applet etc ) , they get a 'ClassNotFoundException' ...

I have tried a bunch of things, and today I did the absolutely last thing that I could think of- Full Xnat Upgrade/Update.
Downloaded the latest Xnat-Builder-dev and rebuilt the whole thing..   did the whole deal ..
Still same problem..   And so I am not sure 'where' the problem is exactly ..?

The error I get is :





And then when I click 'Details' I get this..




Any help in how to go ahead in finding the root of the solution would be greatly appreciated.

P.S: I have Tomcat + Apache2 + modjk

Thanks a lot
Sanket

[Sanket Gupte]

And as before, the images didn't get attached..  so here they are

[Herrick, Rick]

Hey Sanket,

 

The attachments for your screen shots didn’t make it through, so there’s nothing to look at for analysis.

 

A couple of things to try:

 

·         Have you tried any of the steps from this page? https://wiki.xnat.org/display/XNAT16/Troubleshooting+XNAT+Applet+Issues At the very least, these might help get more information about what’s happening.

·         Can your users open ANY applets? The easiest one to try is here: http://java.com/en/download/installed.jsp. Click on that button and see if the verification applet works.

 

Rick Herrick

Sr. Programmer/Analyst

Neuroinformatics Research Group

Washington University School of Medicine

(314) 827-4250

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[Herrick, Rick]

Can you go to the troubleshooting page that I linked to previously and turn the trace logging and other type of logging on?

 

Also, in the ClassNotFoundException dialog, what do you see when you click Details? It’s probably pretty boilerplate, but just in case, I’d like to know what’s there as well.

 

Rick Herrick

Sr. Programmer/Analyst

Neuroinformatics Research Group

Washington University School of Medicine

(314) 827-4250

 

From: xnat_di...@googlegroups.com [mailto:xnat_di...@googlegroups.com] On Behalf Of Sanket Gupte

Sent: Wednesday, June 11, 2014 3:08 PM
To: xnat_di...@googlegroups.com

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[Sanket Gupte]

Thanks Rick,
So I did a bunch of things, and I don't know if this makes things good or bad, but I certainly have more information.

On the xnat VM: the Java check from default website http://java.com/en/download/installed.jsp   fails.  But I read on this link : to try using http://www.javatester.org/version.html  and seems to be working fine.
Also, on the xnat VM, if I open https://localhost  , then all applets work perfect. but opening my xnat outside the VM gives that Class not found error.

There isn't any information on the Java Console that comes up when I click 'Details' on the ClassNotFound error popup box.
The plugin logs are empty.

So, how does it work on the VM itself, but not anywhere else ?

[Sanket Gupte]

I think I must mention that I have openJDK  on the Xnat VM.  (Icedtea plugin for browser)

Also , this setup was working fine once upon a time..  Not sure what exactly triggered it's failure..   But only one of the following two things.
1. Me updating/upgrading the OS
2.  Moving from only tomcat + SSL + port-forwarding  ------ to  ------  > apache w/ SSL + tomcat + modjk

[Bill Schneider]

Hi Sanket,

I had the same problem of applets not working and ClassNotFoundException error messages being displayed. (My XNAT 1.6.3 runs with Java 7, Tomcat 7, and PostgreSQL 9.2 on CentOS Linux.) The error messages in the Firefox Java Console began with the following:

javax.net.ssl.SSLProtocolException: handshake alert:  unrecognized_name

Googling this message led to the solution described on these two web pages.

https://support.roambi.com/hc/en-us/articles/200858194-Cannot-verify-SSL-portal-due-to-error-javax-net-ssl-SSLProtocolException-handshake-alert-unrecognized-name

http://stackoverflow.com/questions/7615645/ssl-handshake-alert-unrecognized-name-error-since-upgrade-to-java-1-7-0

I modified the Apache web server config file and the Tomcat setenv.sh file. The applets worked -- almost.

The ImageJ applet was failing with a NullPointerException error message. I modified the Tomcat context.xml file according to Rick's instructions at

https://groups.google.com/forum/#!topic/xnat_discussion/Av0_N13ThOs

Now the ImageJ applet also works.

Hope this helps.

-- Bill

[Robin Koch]

I'd like to join in on this problem.

I wanted to try the PlexiViewer/ImageJ on our dev-server only to experience that it doesn't work.

What "doesn't work" means:

I click on "View > Images", the popup pops up, the applet tries to load and fails with an "ClassNotFoundException".

What I tried:

1. I tried other xnat-server (like central.xnat.org).
   
   • It works on other xnat-installations.
     So applet per se work!
     
2. I tried the download applet as well.
   
   • It shows the same behavior. Doesn't work on dev, does work on other xnats.
     
3. I followed https://wiki.xnat.org/display/XNAT16/Troubleshooting+XNAT+Applet+Issues
   
   • Clearing the cache had no effect.
   • No matter how I configure the Java Control Panel I can't get the Java Console to give me any output.
     
4. I followed https://docs.oracle.com/javase/tutorial/deployment/applet/problemsindex.html
• The plexiviewer-1.6.4.jar seems fine.
• The applet codebase-path in the HTML-sourcecode looked different than on central.xnat.org and our other xnat ("/xnat/applet" instead of just "/applet"), but:
5. Changing the codebase-path by hand (in the Viewer.vm) to "/applet" didn't have any effect.
   
   • (Which lets me ask again: Where does the variable $!appletPath gets its value from?
     I searched the tomcat- and xnat-folder.)

Any good ideas?

Robin

[Herrick, Rick]

Robin, what operating system are you working on? There are frequent issues on Windows where the process of upgrading the JRE and Java plugin is less than optimal and relics of previous versions end up hanging out like zombie applications. A really common side effect of this is having the Java control panel controlling a JRE and plugin different from the one that’s actually integrated into the browser and a common (in fact, CONSTANT) side effect of that is having the console output in no way correlate to any of the settings you change in the control panel.

Even if you’re not on Windows, it’s still possible this is happening, but I don’t have any direct experience with that.

Also, on the pop-up error message, is there a “More” or “Advanced” option or anything like that? Often they make it hard to find the stack trace info on those dialogs, but know which class is not found would be a good first step.

Another option is to look at the access.log in your XNAT web app logs folder. That may show a failed retrieve of one of the jars for the applet.

-- 

Rick Herrick

Sr. Programmer/Analyst

Neuroinformatics Research Group

Washington University School of Medicine

(314) 740-5961

From: Robin Koch <rko...@googlemail.com>
Reply-To: "xnat_di...@googlegroups.com" <xnat_di...@googlegroups.com>
Date: Thursday, April 23, 2015 at 8:53 AM
To: "xnat_di...@googlegroups.com" <xnat_di...@googlegroups.com>
Subject: [XNAT Discussion] Re: ClassNotFoundException Applet

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[Robin Koch]

Hi Rick,

thanks for your answer. (I wonder why I haven't been informed about it. I just saw it by accident now... But never mind, back to topic!)

I'm on Windows 7/Firefox 37 here and maybe you were right with you suspensions:
Today - after a few tries - the logging works. (Not before I tired another browser and to "debug" a working applet.)

The popup you ask did appear and was in fact the only working way to get the console on screen at all. (By clicking "Details".)

But now I have a log and I'm afraid the problem is about certificats. Yet another topic I never had contact with. %-)

The log says basically the following over and over again:

network: Cache entry not found [url: https://dev.pf-xchg.de/xnat/applet/plexiviewer-1.6.4.jar, version: null]
network: Connecting https://dev.pf-xchg.de/xnat/applet/plexiviewer-1.6.4.jar with proxy=HTTP @ /31.186.227.49:10015
security: Obtain certificate collection in SSL Root CA certificate store
security: Obtain certificate collection in SSL Root CA certificate store
security: Loading certificates from Deployment session certificate store
security: Loaded certificates from Deployment session certificate store
security: SHA-256Certificate finger print: 553113B37BF93324CABBBAF522ADFAE22858A0B66EB68FA790A8AA5A9D293F51
security: Checking if SSL certificate is in Deployment permanent certificate store
security: Obtain certificate collection in SSL Root CA certificate store
security: Obtain certificate collection in SSL Root CA certificate store
security: Obtain certificate collection in SSL Root CA certificate store
security: Obtain certificate collection in SSL Root CA certificate store
network: Connecting http://ocsp2.globalsign.com/gsalphasha2g2 with proxy=HTTP @ /31.186.227.49:10015
network: Server http://ocsp2.globalsign.com/gsalphasha2g2 requesting to set-cookie with "__cfduid=d41e470cd6d6e494c22127d31ea62ed951429860271; expires=Sat, 23-Apr-16 07:24:31 GMT; path=/; domain=.globalsign.com; HttpOnly"
security: Failing over to CRLs: java.security.cert.CertPathValidatorException: Responder's certificate is not authorized to sign OCSP responses
cache: Resource http://crl2.alphassl.com/gs/gsalphasha2g2.crl has future expires: Tue Apr 28 09:07:18 CEST 2015 update check skipped.
javax.net.ssl.SSLHandshakeException: java.security.cert.CertificateException: java.security.cert.CertPathValidatorException: Responder's certificate is not authorized to sign OCSP responses
[...]

Robin

[Robin Koch]

Ok, the applet loads after following this:

https://community.oracle.com/thread/3697629

Yet I'm not sure that's the best practice to handle this.

Robin

[Herrick, Rick]

Yeah, that’s a new one on me. I’ve been running 8u40 for a while now and the applet works without a problem. I think that the certificate at issue is the certificate being used for SSL on your proxy, maybe Apache HTTPD or nginx. That is, it’s not the signing certificate we use to sign the applet jars, I think it’s the applet complaining about the SSL certificate on your server. I think. Who knows, they introduce new issues with SSL certs on an almost daily basis, it seems.

-- 

Rick Herrick

Sr. Programmer/Analyst

Neuroinformatics Research Group

Washington University School of Medicine

(314) 740-5961

From: Robin Koch <rko...@googlemail.com>
Reply-To: "xnat_di...@googlegroups.com" <xnat_di...@googlegroups.com>
Date: Friday, April 24, 2015 at 3:06 AM
To: "xnat_di...@googlegroups.com" <xnat_di...@googlegroups.com>

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