In the Processes tab of your Joget app, images of your processes will be generated and updated under certain circumstances (e.g. process diagram update). The images may not get generated under certain circumstances.
The message below will stay the same for a prolonged period or you may get a blank image if the generation fails.
Figure 1: Process thumbnail not being generated
Possible problem 1 - Permission access on home folder
You may need to grant sufficient read/write permission to the /wflow home folder.
Start up your Joget server using the same user with the permission to access the folder.
Possible problem 2 - java.awt.headless error
Caused by: java.awt.HeadlessException: No X11 DISPLAY variable was set, but this program performed an operation which requires it. at java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:207)
Caused by: java.awt.HeadlessException: No X11 DISPLAY variable was set, but this program performed an operation which requires it. at java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:159) at java.awt.Window.<init>(Window.java:433) at java.awt.Frame.<init>(Frame.java:403) at java.awt.Frame.<init>(Frame.java:368) at javax.swing.SwingUtilities$SharedOwnerFrame.<init>(SwingUtilities.java:1733) at javax.swing.SwingUtilities.getSharedOwnerFrame(SwingUtilities.java:1810) at javax.swing.JDialog.<init>(JDialog.java:253) at javax.swing.JDialog.<init>(JDialog.java:187) at javax.swing.JDialog.<init>(JDialog.java:160)
The server that hosts Joget may not have full graphic support, therefore, you can try to run the server in headless mode by adding the following parameter to the startup script (i.e. tomcat6.sh) under JAVA_OPTS.
-Djava.awt.headless=true
More references:
http://stackoverflow.com/questions/5576986/servlet-giving-error-java-lang-noclassdeffounderror
https://wiki.jenkins-ci.org/display/JENKINS/Jenkins+got+java.awt.headless+problem
http://dev.joget.org/community/pages/viewpage.action?pageId=12976186
Possible problem 3 - Domain/DNS/Routing issue
ERROR 04 Nov 2014 22:47:22 org.joget.workflow.util.XpdlImageUtil - Error generating xpdl image [processDefId=ABC#7#WPIApplication] java.net.ConnectException: Connection refused: connect
A http call will be made when a process thumbnail is being generated.
You will need to make sure that you are able to ping/call to the domain itself from the server that is hosting Joget itself. (e.g. your domain is gojoget.com - from your server, you must be able to ping to gojoget.com as well)
If you are facing similar issue such as this, try to modify your host file so that it would redirect to your localhost.
Example:-
# ip<space>domain 201.225.100.01 localhost
Possible problem 4 - Outdated cached process images
If you have tried out the solutions above and still can't get it to work, then you may try to clear the cached images from your Joget home folder (typically located at [USER]/wflow/app_xpdlImages ) Refresh your browser page so that it will attempt to generate new thumbnails again.