I'm having some problems tracing the reason that I can't load a java(fx) applet.
The java plugin console for the browser has always been my sole source of information for problem solving. The reason it isn't much help at the moment is that the applet starts to load, downloading the jar files and outputting a percentage to the console along with the occasional statement to say it's on the next jar file. At some point in time (different percentages each time) the console just closes unexpectedly and the applet stops loading. I know this isn't much to go on but I was wondering if there was any way that the output from the console could be stored to a file on the local machine. To debug this particular problem, changing security permissions temporarily would be acceptable.
The problem has occured on every pc i've tried, however if I keep refreshing after failure it seems to cache the jar files previously downloaded and thus get further through the loading process until it eventually works. My issue now is that on a particular customers network refreshing does not resolve the issue. I thought it may be a permissions issue writing to disk but I've tried an administrator account and still no luck. I've also tried a variety of browsers. It might also be worth noting that they go through a proxy server - when the applet tries to load it asks for the credentials for logging on to the proxy which seems to authorise fine.
If anyone has a suggestion on what I could try it would be gratefully received.
Thanks,
James
Two points:
You should be able to get a stack trace through the applet console viewer (which runs in the system tray on PC's) and if you open that up it will show you your stack trace for debugging.
Can you reproduce this problem using the Java Applet Viewer tool? This will allow you to write unit tests, and debug much more easily.
I forget where it is, but somewhere in the java control panel (one of the options under the advanced tab I believe) there's an option to turn on logging. This will log all output to the java console to a file as well. I've used this when trying to debug issues similar to this.
There's some info here on where the files will appear:
http://download.oracle.com/javase/1.5.0/docs/guide/deployment/deployment-guide/tracing_logging.html
The problem ended up being some JS code that was making calls to the applet before the applet had initialised.
Related
My setup:
Red Hat with:
Weblogic installation which hosts my (java) application.
What I try to achieve:
See the output (an error) of my application
Why I this way and not easier (set proper logging on the application itself):
This is a production server of a big company, I am not allowed to do any changes to the running applications
In the application something goes wrong and I am tasked with fixing it.
I checked the weblogic logs but they dont capture all the output of the application, and thus it does not capture the error im searching for.
So is there a way I can sort of connect to stdout/stderr and see the output printed live? (other suggestions are also most welcome but if its possible this seems like the easiest way to go?)
Extra info:
I have checked and confirmed the application writes to console, so it should appear in stdout. (right?)
Unless I misunderstand your question, you want to tail the logs.
Navigate to the directory where your logs are stored and run
tail -f LOGNAME.log
This should print to your console live any additional log lines that are added.
I am working on a java ee web application in NetBeans. I am trying to debug the behavior of the application but the behavior I'm seeing is confusing.
I am running the application through NetBeans in Tomcat. Within NetBeans, I select "Debug" from the root of the Project Tree and I can send one request to the application I've written. Breakpoints are hit and I get unique results from the application.
However, every subsequent time I try to send a request to my application, I get the exact same incorrect result (even if I clear the cache on Chrome) and the Netbeans IDE doesn't stop at any of the defined breakpoints. Is this to be expected? Does a Servlet get mangled in memory once it runs through the debugger once? Do I need to stop and restart/reattach the NetBeans debugger every time I want to debug the application? Is there something I'm doing wrong when using the debugger? Does this indicate a problem with the code I've written in my Servlet?
Thanks,
Jason Mazzotta
rjsang's point on the cache might be valid, and is worth investigating.
However, it might also be that something is breaking earlier than you expect, causing you to never even reach the break pointed lines.
I would suggest:
Look into liberally sprinkling your code with debug logging statements (using a good logging framework such as Log4J with SLF4j)
Throw more breakpoints at the problem - start with the very first line you expect to be hit from your request. And the go even higher/earlier, if possible.
Tail that Tomcat log (catalina.out) - you might spot something catastrophic happening there.
Good luck.
I've taken a job where years ago their webmaster setup an intranet using Tomcat on a linux server. The users can create something in the test environment and then click "make live" and the Linux/Tomcat moves the file to a Linux/live PHP web setup.
I'm clueless how they're moving the files. What would be a common tool to do this in Tomcat and Java?
I realize this is vague, but any help would be appreciated. Let me know what other info would be needed.
Also there is a duplicate MySQL database in both servers. I'm guessing the Tomcat setup is writing duplicate info to both databases, but I don't see how the files are getting moved.
This sounds like the website content is completely stored in the database and written over to the other server.
Theoretically you could also have a rsync shell script and call that from php to actually synchronize files over to the other server.
If the "Make Live" is on click and happens immediately its either a direct db access or some script based synchronization.
If it takes a while it could be a cron-job. Maybe you should just check this anway crontab -l will work.
There are several options, you actually open the *.php which the user can edit the content and see where the make live button brings you e.g. "Post Form to *.php" and than you check what that script is doing or you show us the package (what i would like to see but not suggest if you are working on a companies site).
Get back here with some more information, so i can expand the answer for you. Maybe you should also clarify why you are clueless, state what you have checked already, the info i would require is the actual site which has the make live button on it, it will lead to the next site or a script which will probably show what the site is doing.
Recently two of our clients have reported problems with our applets. Looking at the java plugin console it is full of ClassNotFoundException so none of our code is executed.
I've been able to reproduce the stack trace using a virtual pc image with 0 free space on disk, but the problem goes away as I restore some disk space, and the users tell me that their disk is not full; they are able to create new files.
Our applet requires java 6, and the problem has appeared with updates 1, 10 and 14 of the jre. We have also tried different browsers (IE and Firefox), clearing the browser and java caches, ...
How can I debug or trace what is the jvm doing to load our applet?
I suppose that the problem lies on some security directive on windows so I'm using Sysinternal's Process Monitor to log the activity but I don't really know where to look at.
The Java cache is most likely messed up. Open Java in the Control Panel and get rid of all temporary files to see if it goes away.
Logging in the Java Console for loading applets can be enabled which helps quite alot (even if the plugin is extremely cryptic). See http://java.sun.com/javase/6/docs/technotes/guides/deployment/deployment-guide/tracing_logging.html
I've been looking at the plugin source from the JDK and I've found that there is additional debug info available in the logs setting the environment variable JPI_PLUGIN2_DEBUG.
Unfortunately I still only see ClassNotFound exceptions.
I've found a piece of the plugin code that swallows all exceptions, so maybe my users problem is there...
had similar problems a while ago. In our case, the problem seems to be how the applet tag is set up on the web page. If it is in a wrong order or contains the codebase attribute, it fails with 6u10+. This works for us:
<applet name="DMGANTT" archive="DMGantt.zip" code="dm.applet.DMGanttApplet"
width='100%' height='100%' mayscript="mayscript">
We had a similar problem with one of our clients. We discovered that it was a strange bug in some versions of Java related to proxy configuration on the client. See this article for the details
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6723715
Also, our applet failed with new versions for a different reason.
Now, in similar cases I ask them to check javatester.org, so that I can see if applets (in general) load OK in their browser. If that page loads OK, its a problem on our applet (or page). Else it's a problem in their configuration. I help them anyway but it's easier to debug.
I am working on a demo for a client of what's possible with GWT-Ext for GWT. After browsing for the simplest way to get up and running, I decided on installing the Google Plugin for Eclipse and using the New Web Application Wizard.
First time around, I followed these steps for create the default application:
Selected File > New > Web Application Project from the Eclipse menu.
In the New Web Application Project wizard, entered a name for the project (ExtDemo) and a java package name, com.extdemo.
Unchecked the "Use Google App Engine" check box.
Clicked Finish.
Right clicked it in package explorer and selected Run As > Run Configurations
Put a check in the Automatically Select Unused Port checkbox.
Clicked Run to see the default GWT 1.7 application
This worked fine... it launched GWT's hosted browser and the app worked as supposed to.
(I then continued to import GWT-Ext and add all sorts of widgets building up a nice little demo app)
However at some point when relaunching the app in hosted mode, the hosted browser displays an empty iframe. I even reverted the code to a point where everything was working as supposed to and... same thing, an empty iframe with the surrounding static content.
Now what is really strange is when I go through the process of creating the default application again by following the steps above, the hosted browser launches with an empty iframe again.
However when I click on Compile/Browse, this sometimes allows the app to launch in Firefox.
Anyone have this happen to them?
I have seen some odd behaviors occasionally. Here are some basic suggestions (some are dumb and you might have tried them already):
Use a new workspace
I do not know if GWT plugin somehow caches stuff in the embedded Jetty. If you are re-creating the default app/project, try and use a different name for the project.
Try and re-use a fixed port so that there is no possibility of having multiple servers running.
Update: Found a new "classic" solution:
Delete the cache in IE and possibly Firefox too. Apparently the 'script' tag content tends to be cached by IE. If this works, we can all try tearing our hair out!
Found the updated answer at this link:
I have had the same problem in the past and found it is much more likely to happen if limited CPU is available. For example if my older laptop was running on battery and had stepped down the CPU speed to save power it frequently happened. When running on mains in max performance mode it only happened occasionally. Now I have a much newer and more powerful laptop and the problem has gone away.
Another cause I found was too many breakpoints set up in eclipse and removing breakpoints would often clear the problem.
I've had issues with the browser caching.
Try clearing your browser cache, refresh a few times after a failed load, etc.
You can also try using a different port so the URL is different.
It takes some time to download and run the GWT app, particularly if you are using extra libraries, so wait for a few seconds to see if the app finally loaded.
What makes the app loading to fail randomly is something I don't know yet, but I suspect, as stated by Daniel Vaughan, that is related with a lack of computer resources, CPU, memory, etc.