Package org.apache.commons.vfs2.impl

Class DefaultFileMonitor

java.lang.Object
org.apache.commons.vfs2.impl.DefaultFileMonitor
All Implemented Interfaces:
AutoCloseable, Runnable, FileMonitor
public class DefaultFileMonitor extends Object implements Runnable, FileMonitor, AutoCloseable
A polling FileMonitor implementation.

The DefaultFileMonitor is a Thread based polling file system monitor with a 1 second delay.

Design:

There is a Map of monitors known as FileMonitorAgents. With the thread running, each FileMonitorAgent object is asked to "check" on the file it is responsible for. To do this check, the cache is cleared.

  • If the file existed before the refresh and it no longer exists, a delete event is fired.
  • If the file existed before the refresh and it still exists, check the last modified timestamp to see if that has changed.
  • If it has, fire a change event.

With each file delete, the FileMonitorAgent of the parent is asked to re-build its list of children, so that they can be accurately checked when there are new children.

New files are detected during each "check" as each file does a check for new children. If new children are found, create events are fired recursively if recursive descent is enabled.

For performance reasons, added a delay that increases as the number of files monitored increases. The default is a delay of 1 second for every 1000 files processed.

Example usage:

 FileSystemManager fsManager = VFS.getManager();
 FileObject listenDir = fsManager.resolveFile("/home/username/monitored/");

 DefaultFileMonitor fm = new DefaultFileMonitor(new CustomFileListener());
 fm.setRecursive(true);
 fm.addFile(listenDir);
 fm.start();
(where CustomFileListener is a class that implements the FileListener interface.)

  • Field Details

    • THREAD_FACTORY

      private static final ThreadFactory THREAD_FACTORY

    • LOG

      private static final org.apache.commons.logging.Log LOG

    • DEFAULT_DELAY

      private static final Duration DEFAULT_DELAY

    • DEFAULT_MAX_FILES

      private static final int DEFAULT_MAX_FILES
      See Also:

    • monitorMap

      private final Map<FileName,DefaultFileMonitor.FileMonitorAgent> monitorMap
      Map from FileName to FileObject being monitored.

    • monitorThread

      private Thread monitorThread
      The low priority thread used for checking the files being monitored.

    • deleteStack

      private final Stack<FileObject> deleteStack
      File objects to be removed from the monitor map.

    • addStack

      private final Stack<FileObject> addStack
      File objects to be added to the monitor map.

    • runFlag

      private volatile boolean runFlag
      A flag used to determine if the monitor thread should be running.

    • recursive

      private boolean recursive
      A flag used to determine if adding files to be monitored should be recursive.

    • delay

      private Duration delay
      Sets the delay between checks

    • checksPerRun

      private int checksPerRun
      Sets the number of files to check until a delay will be inserted

    • listener

      private final FileListener listener
      A listener object that if set, is notified on file creation and deletion.

  • Constructor Details

    • DefaultFileMonitor

      public DefaultFileMonitor(FileListener listener)
      Constructs a new instance with the given listener.
      Parameters:
      listener - the listener.

  • Method Details

    • addFile

      public void addFile(FileObject file)
      Adds a file to be monitored.
      Specified by:
      addFile in interface FileMonitor
      Parameters:
      file - The FileObject to monitor.

    • close

      public void close()
      Specified by:
      close in interface AutoCloseable

    • getChecksPerRun

      public int getChecksPerRun()
      Gets the number of files to check per run.
      Returns:
      The number of files to check per iteration.

    • getDelay

      @Deprecated public long getDelay()
      Deprecated.
      Use getDelayDuration().
      Gets the delay between runs.
      Returns:
      The delay period in milliseconds.

    • getDelayDuration

      public Duration getDelayDuration()
      Gets the delay between runs.
      Returns:
      The delay period.

    • getFileListener

      FileListener getFileListener()
      Gets the current FileListener object notified when there are changes with the files added.
      Returns:
      The FileListener.

    • isRecursive

      public boolean isRecursive()
      Tests the recursive setting when adding files for monitoring.
      Returns:
      true if monitoring is enabled for children.

    • queueAddFile

      protected void queueAddFile(FileObject file)
      Queues a file for addition to be monitored.
      Parameters:
      file - The FileObject to add.

    • queueRemoveFile

      protected void queueRemoveFile(FileObject file)
      Queues a file for removal from being monitored.
      Parameters:
      file - The FileObject to be removed from being monitored.

    • removeFile

      public void removeFile(FileObject file)
      Removes a file from being monitored.
      Specified by:
      removeFile in interface FileMonitor
      Parameters:
      file - The FileObject to remove from monitoring.

    • run

      public void run()
      Asks the agent for each file being monitored to check its file for changes.
      Specified by:
      run in interface Runnable

    • setChecksPerRun

      public void setChecksPerRun(int checksPerRun)
      Sets the number of files to check per run. An additional delay will be added if there are more files to check.
      Parameters:
      checksPerRun - a value less than 1 will disable this feature

    • setDelay

      public void setDelay(Duration delay)
      Sets the delay between runs.
      Parameters:
      delay - The delay period.
      Since:
      2.10.0

    • setDelay

      @Deprecated public void setDelay(long delay)
      Deprecated.
      Use setDelay(Duration).
      Sets the delay between runs.
      Parameters:
      delay - The delay period in milliseconds.

    • setRecursive

      public void setRecursive(boolean newRecursive)
      Sets the recursive setting when adding files for monitoring.
      Parameters:
      newRecursive - true if monitoring should be enabled for children.

    • start

      public void start()
      Starts monitoring the files that have been added.

    • stop

      public void stop()
      Stops monitoring the files that have been added.