Webslinger cowstate.xml error

[Kaushik Chakraborty-2]

Hi,

Its a content management application. I created some folders / files  
and then deleted some files, all from the application and not from the  
backend. It behaves properly most of the time but sometimes it throws  
below exception.

[StandardWrapperValve.java:257:ERROR] Servlet.service() for servlet  
WebslingerServlet threw exception
java.lang.NullPointerException
         at  
org.webslinger.commons.vfs.handlers.cow.COWStateXmlStorageHandler
$1.findIfExists(COWStateXmlStorageHandler.java:19)
         at  
org.webslinger.commons.vfs.handlers.cow.COWStateXmlStorageHandler
$1.findIfExists(COWStateXmlStorageHandler.java:16)
         at org.webslinger.lang.ConcurrentCache.findIfExists
(ConcurrentCache.java:39)
         at org.webslinger.lang.AbstractCache$ConcurrentDelegate.get
(AbstractCache.java:125)
         at org.webslinger.lang.AbstractCache.get(AbstractCache.java:
287)
         at org.webslinger.lang.ConcurrentCache.get
(ConcurrentCache.java:29)
         at  
org.webslinger.commons.vfs.handlers.cow.COWStateXmlStorageHandler.removeDeletedChildren
(COWStateXmlStorageHandler.j
ava:43)
         at org.webslinger.commons.vfs.virtual.VirtualFileSystem
$VirtualResolution.getChildNames(VirtualFileSystem.java:542)
         at  
org.webslinger.commons.vfs.GenerationalFileObject.doListChildren
(GenerationalFileObject.java:51)
         at  
org.webslinger.commons.vfs.AbstractGenerifiedFileObject.resolveChildren
(AbstractGenerifiedFileObject.java:69)
         at  
org.webslinger.commons.vfs.AbstractGenerifiedFileObject.getChildren
(AbstractGenerifiedFileObject.java:54)
         at  
org.webslinger.commons.vfs.GenerationalFileObject.getChildren
(GenerationalFileObject.java:46)
         at  
org.webslinger.commons.vfs.flat.FlatFileObject.doListChildren
(FlatFileObject.java:103)
         at  
org.webslinger.commons.vfs.AbstractGenerifiedFileObject.resolveChildren
(AbstractGenerifiedFileObject.java:69)
         at  
org.webslinger.commons.vfs.AbstractGenerifiedFileObject.getChildren
(AbstractGenerifiedFileObject.java:54)
         at org.webslinger.commons.vfs.virtual.VirtualFileSystem
$VirtualResolution.getChildNames(VirtualFileSystem.java:526)
         at  
org.webslinger.commons.vfs.GenerationalFileObject.doListChildren
(GenerationalFileObject.java:51)

I could see that the folder where files have been deleted contain  
a .cowstate.xml which has following entry for each file deleted from  
the application

        <item deleted="true" name="<file name>"/>

I saw the code of the COWStateXmlStorageHandler constructor where a  
new ConcurrentCache object has been created which contains the method  
findIfExists(). Now from the method's name, I am assuming that it is  
searching for the file ".cowstate.xml" using getFile() method. But as  
I cannot debug it I am clueless that why the returned File object is  
null and hence file.exists() is throwing the above  
NullPointerException. Is it a OS issue that getFile() is failing? The  
constructor code of  COWStateXmlStorageHandler is here

public COWStateXmlStorageHandler() {
         states = new ConcurrentCache<FileName, COWStateXml>
(COWStateXmlStorageHandler.class, "states", null,  
ConcurrentCache.SOFT) {
             protected COWStateXml findIfExists(FileName key) throws  
Exception {
                 FileObject file = getFile(key);
                 return file.exists() ? new COWStateXml(file) : null;
             }

             protected COWStateXml createValue(FileName key) throws  
Exception {
                 return new COWStateXml(getFile(key));
             }
         };
     }


Please help as these errors are now coming frequently and is causing  
much trouble.

Thanks,
Kaushik

[Kaushik Chakraborty-2]

I deleted the .cowstate.xml file and then everything seemed fine. But  
again this morning I found the same exception. Is the .cowstate.xml  
remains somewhere in the cache which Webslinger uses? I restarted the  
server, to flush the cache, and everything again is fine.

Please help as there is no place I can find help on Webslinger other  
than here.

Adam / Ean  - Please share some light on the issue. Its kind of urgent.

Thanks,
Kaushik


On 10-Oct-2009, at 12:20 PM, Kaushik Chakraborty wrote:

> Hi,
>
> Its a content management application. I created some folders / files  
> and then deleted some files, all from the application and not from  
> the backend. It behaves properly most of the time but sometimes it  
> throws below exception.
>
> [StandardWrapperValve.java:257:ERROR] Servlet.service() for servlet  
> WebslingerServlet threw exception
> java.lang.NullPointerException
>         at  
> org.webslinger.commons.vfs.handlers.cow.COWStateXmlStorageHandler
> $1.findIfExists(COWStateXmlStorageHandler.java:19)
>         at  
> org.webslinger.commons.vfs.handlers.cow.COWStateXmlStorageHandler
> $1.findIfExists(COWStateXmlStorageHandler.java:16)
>         at org.webslinger.lang.ConcurrentCache.findIfExists
> (ConcurrentCache.java:39)
>         at org.webslinger.lang.AbstractCache$ConcurrentDelegate.get
> (AbstractCache.java:125)
>         at org.webslinger.lang.AbstractCache.get(AbstractCache.java:
> 287)
>         at org.webslinger.lang.ConcurrentCache.get
> (ConcurrentCache.java:29)
>         at  
> org.webslinger.commons.vfs.handlers.cow.COWStateXmlStorageHandler.removeDeletedChildren
> (COWStateXmlStorageHandler.j
> ava:43)
>         at org.webslinger.commons.vfs.virtual.VirtualFileSystem
> $VirtualResolution.getChildNames(VirtualFileSystem.java:542)
>         at  
> org.webslinger.commons.vfs.GenerationalFileObject.doListChildren
> (GenerationalFileObject.java:51)
>         at  
> org.webslinger.commons.vfs.AbstractGenerifiedFileObject.resolveChildren
> (AbstractGenerifiedFileObject.java:69)
>         at  
> org.webslinger.commons.vfs.AbstractGenerifiedFileObject.getChildren
> (AbstractGenerifiedFileObject.java:54)
>         at  
> org.webslinger.commons.vfs.GenerationalFileObject.getChildren
> (GenerationalFileObject.java:46)
>         at  
> org.webslinger.commons.vfs.flat.FlatFileObject.doListChildren
> (FlatFileObject.java:103)
>         at  
> org.webslinger.commons.vfs.AbstractGenerifiedFileObject.resolveChildren
> (AbstractGenerifiedFileObject.java:69)
>         at  
> org.webslinger.commons.vfs.AbstractGenerifiedFileObject.getChildren
> (AbstractGenerifiedFileObject.java:54)
>         at org.webslinger.commons.vfs.virtual.VirtualFileSystem
> $VirtualResolution.getChildNames(VirtualFileSystem.java:526)
>         at  
> org.webslinger.commons.vfs.GenerationalFileObject.doListChildren
> (GenerationalFileObject.java:51)
>
> I could see that the folder where files have been deleted contain  
> a .cowstate.xml which has following entry for each file deleted from  
> the application
>
> <item deleted="true" name="<file name>"/>
>
> I saw the code of the COWStateXmlStorageHandler constructor where a  
> new ConcurrentCache object has been created which contains the  
> method findIfExists(). Now from the method's name, I am assuming  
> that it is searching for the file ".cowstate.xml" using getFile()  
> method. But as I cannot debug it I am clueless that why the returned  
> File object is null and hence file.exists() is throwing the above  
> NullPointerException. Is it a OS issue that getFile() is failing?  
> The constructor code of  COWStateXmlStorageHandler is here
>
> public COWStateXmlStorageHandler() {
>         states = new ConcurrentCache<FileName, COWStateXml>
> (COWStateXmlStorageHandler.class, "states", null,  
> ConcurrentCache.SOFT) {
>             protected COWStateXml findIfExists(FileName key) throws  
> Exception {
>                 FileObject file = getFile(key);
>                 return file.exists() ? new COWStateXml(file) : null;
>             }
>
>             protected COWStateXml createValue(FileName key) throws  
> Exception {
>                 return new COWStateXml(getFile(key));
>             }
>         };
>     }
>
>
> Please help as these errors are now coming frequently and is causing  
> much trouble.
>
> Thanks,
> Kaushik
>