Re: [VFS]: NPE in FileObject.getType().getChildren()

Mario Ivankovits Thu, 20 May 2004 22:53:30 -0700

Paul Smith wrote:

I am getting an NPE in the following line of code, and I think it must be
thread related or something.

I have tried to reproduce it, but wasnt able to.

I collected your code into an test-class, not knowing if this is really what happens on your machine.

vfs itself do not use threading, and in your case, if it cant determine the type (=null) is is used IMAGINARY by default and thus cant be null.- i wonder how your NPE can happen. But vfs itself is not thread save, if you access the same fileobject from two thread you should synchronize on them.

...

Now i have found a way, how this could happen too. If vfs cant determine the type the fileobject is already in state "attached" but the type is null then. However, an exception should have been thrown. Maybe your posted exception is only the aftereffect from another exception before?

Could you please have a look in this direction. Also please try this code - and eventually complete it to make them throw the exception.

--Mario

---cut---
/*
* Copyright 2002, 2003,2004 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.vfs.example;

import org.apache.commons.vfs.FileObject;
import org.apache.commons.vfs.FileSystemManager;
import org.apache.commons.vfs.VFS;
import org.apache.commons.vfs.FileSystemException;

import java.io.File;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;

public class VFSChainsaw
{
   public static void main(String[] args) throws Exception
   {
       FileSystemManager fileSystemManager = VFS.getManager();

       File[] roots = File.listRoots();
       for (int i = 0; i < roots.length; i++)
       {
           File root = roots[i];

           /* uncomment to recurse only a specific driver
           if (!root.getAbsolutePath().toLowerCase().startsWith("x:"))
           {
               continue;
           }
           */

           if (!(root.getAbsolutePath().toLowerCase().startsWith("a:") ||
               root.getAbsolutePath().toLowerCase().startsWith("b:")))
           {
               if (root.exists() && root.canRead())
               {
                   FileObject fileObject = fileSystemManager
                       .resolveFile(root.toURL().toExternalForm());

System.err.println("local:" + root.getAbsolutePath() + " fo:" + fileObject);

                   int count = recurse(fileObject);
                   System.err.println("Number Of files: "+ count);
               }
           }
       }
   }

private static int recurse(FileObject fileObject) throws FileSystemException { int count = 0;

       FileObject[] fos = fileObject.getChildren();
       Collection objects = new ArrayList(Arrays.asList(fos));
       for (Iterator iter = objects.iterator(); iter.hasNext();)
       {
           count++;
           FileObject fo = (FileObject) iter.next();
           if (fo.getType().hasChildren())
           {
               // System.err.println("child:" + fo);
               iter.remove();

               count+=recurse(fo);
           }
       }

       return count;
   }
}
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Re: [VFS]: NPE in FileObject.getType().getChildren()

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