org.apache.commons.io

Class DirectoryWalker<T>

  • Type Parameters:
    T - The result type, like File.

    @Deprecated
    public abstract class DirectoryWalker<T>
    extends Object
    Abstract class that walks through a directory hierarchy and provides subclasses with convenient hooks to add specific behavior.

    This class operates with a FileFilter and maximum depth to limit the files and directories visited. Commons IO supplies many common filter implementations in the filefilter package.

    The following sections describe:

    1. Example Implementation

    There are many possible extensions, for example, to delete all files and '.svn' directories, and return a list of deleted files:
     public class FileCleaner extends DirectoryWalker {
    
         public FileCleaner() {
             super();
         }
    
         public List clean(File startDirectory) {
             List results = new ArrayList();
             walk(startDirectory, results);
             return results;
         }
    
         protected boolean handleDirectory(File directory, int depth, Collection results) {
             // delete svn directories and then skip
             if (".svn".equals(directory.getName())) {
                 directory.delete();
                 return false;
             } else {
                 return true;
             }
    
         }
    
         protected void handleFile(File file, int depth, Collection results) {
             // delete file and add to list of deleted
             file.delete();
             results.add(file);
         }
     }
     

    2. Filter Example

    Choosing which directories and files to process can be a key aspect of using this class. This information can be setup in three ways, via three different constructors.

    The first option is to visit all directories and files. This is achieved via the no-args constructor.

    The second constructor option is to supply a single FileFilter that describes the files and directories to visit. Care must be taken with this option as the same filter is used for both directories and files.

    For example, if you wanted all directories which are not hidden and files which end in ".txt":

     public class FooDirectoryWalker extends DirectoryWalker {
         public FooDirectoryWalker(FileFilter filter) {
             super(filter, -1);
         }
     }
    
     // Build up the filters and create the walker
     // Create a filter for Non-hidden directories
     IOFileFilter fooDirFilter = FileFilterUtils.andFileFilter(FileFilterUtils.directoryFileFilter,
         HiddenFileFilter.VISIBLE);
    
     // Create a filter for Files ending in ".txt"
     IOFileFilter fooFileFilter = FileFilterUtils.andFileFilter(FileFilterUtils.fileFileFilter,
         FileFilterUtils.suffixFileFilter(".txt"));
    
     // Combine the directory and file filters using an OR condition
     java.io.FileFilter fooFilter = FileFilterUtils.orFileFilter(fooDirFilter, fooFileFilter);
    
     // Use the filter to construct a DirectoryWalker implementation
     FooDirectoryWalker walker = new FooDirectoryWalker(fooFilter);
     

    The third constructor option is to specify separate filters, one for directories and one for files. These are combined internally to form the correct FileFilter, something which is very easy to get wrong when attempted manually, particularly when trying to express constructs like 'any file in directories named docs'.

    For example, if you wanted all directories which are not hidden and files which end in ".txt":

      public class FooDirectoryWalker extends DirectoryWalker {
        public FooDirectoryWalker(IOFileFilter dirFilter, IOFileFilter fileFilter) {
          super(dirFilter, fileFilter, -1);
        }
      }
    
      // Use the filters to construct the walker
      FooDirectoryWalker walker = new FooDirectoryWalker(
        HiddenFileFilter.VISIBLE,
        FileFilterUtils.suffixFileFilter(".txt"),
      );
     

    This is much simpler than the previous example, and is why it is the preferred option for filtering.

    3. Cancellation

    The DirectoryWalker contains some of the logic required for cancel processing. Subclasses must complete the implementation.

    What DirectoryWalker does provide for cancellation is:

    Implementations need to provide:

    • The decision logic on whether to cancel processing or not.
    • Constructing and throwing a DirectoryWalker.CancelException.
    • Custom cancel processing in the handleCancelled() method.

    Two possible scenarios are envisaged for cancellation:

    The following sections provide example implementations for these two different scenarios.

    3.1 External / Multi-threaded

    This example provides a public cancel() method that can be called by another thread to stop the processing. A typical example use-case would be a cancel button on a GUI. Calling this method sets a volatile flag to ensure it will work properly in a multi-threaded environment. The flag is returned by the handleIsCancelled() method, which will cause the walk to stop immediately. The handleCancelled() method will be the next, and last, callback method received once cancellation has occurred.

     public class FooDirectoryWalker extends DirectoryWalker {
    
         private volatile boolean cancelled = false;
    
         public void cancel() {
             cancelled = true;
         }
    
         protected boolean handleIsCancelled(File file, int depth, Collection results) {
             return cancelled;
         }
    
         protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
             // implement processing required when a cancellation occurs
         }
     }
     

    3.2 Internal

    This shows an example of how internal cancellation processing could be implemented. Note the decision logic and throwing a DirectoryWalker.CancelException could be implemented in any of the lifecycle methods.

     public class BarDirectoryWalker extends DirectoryWalker {
    
         protected boolean handleDirectory(File directory, int depth, Collection results) throws IOException {
             // cancel if hidden directory
             if (directory.isHidden()) {
                 throw new CancelException(file, depth);
             }
             return true;
         }
    
         protected void handleFile(File file, int depth, Collection results) throws IOException {
             // cancel if read-only file
             if (!file.canWrite()) {
                 throw new CancelException(file, depth);
             }
             results.add(file);
         }
    
         protected void handleCancelled(File startDirectory, Collection results, CancelException cancel) {
             // implement processing required when a cancellation occurs
         }
     }
     
    Since:
    1.3
    • Constructor Detail

      • DirectoryWalker

        protected DirectoryWalker()
        Deprecated. 
        Construct an instance with no filtering and unlimited depth.
      • DirectoryWalker

        protected DirectoryWalker(FileFilter filter,
                                  int depthLimit)
        Deprecated. 
        Constructs an instance with a filter and limit the depth navigated to.

        The filter controls which files and directories will be navigated to as part of the walk. The FileFilterUtils class is useful for combining various filters together. A null filter means that no filtering should occur and all files and directories will be visited.

        Parameters:
        filter - the filter to apply, null means visit all files
        depthLimit - controls how deep the hierarchy is navigated to (less than 0 means unlimited)
      • DirectoryWalker

        protected DirectoryWalker(IOFileFilter directoryFilter,
                                  IOFileFilter fileFilter,
                                  int depthLimit)
        Deprecated. 
        Constructs an instance with a directory and a file filter and an optional limit on the depth navigated to.

        The filters control which files and directories will be navigated to as part of the walk. This constructor uses FileFilterUtils.makeDirectoryOnly(IOFileFilter) and FileFilterUtils.makeFileOnly(IOFileFilter) internally to combine the filters. A null filter means that no filtering should occur.

        Parameters:
        directoryFilter - the filter to apply to directories, null means visit all directories
        fileFilter - the filter to apply to files, null means visit all files
        depthLimit - controls how deep the hierarchy is navigated to (less than 0 means unlimited)
    • Method Detail

      • walk

        protected final void walk(File startDirectory,
                                  Collection<T> results)
                           throws IOException
        Deprecated. 
        Internal method that walks the directory hierarchy in a depth-first manner.

        Users of this class do not need to call this method. This method will be called automatically by another (public) method on the specific subclass.

        Writers of subclasses should call this method to start the directory walk. Once called, this method will emit events as it walks the hierarchy. The event methods have the prefix handle.

        Parameters:
        startDirectory - the directory to start from, not null
        results - the collection of result objects, may be updated
        Throws:
        NullPointerException - if the start directory is null
        IOException - if an I/O Error occurs
      • checkIfCancelled

        protected final void checkIfCancelled(File file,
                                              int depth,
                                              Collection<T> results)
                                       throws IOException
        Deprecated. 
        Checks whether the walk has been cancelled by calling handleIsCancelled(java.io.File, int, java.util.Collection<T>), throwing a CancelException if it has.

        Writers of subclasses should not normally call this method as it is called automatically by the walk of the tree. However, sometimes a single method, typically handleFile(java.io.File, int, java.util.Collection<T>), may take a long time to run. In that case, you may wish to check for cancellation by calling this method.

        Parameters:
        file - the current file being processed
        depth - the current file level (starting directory = 0)
        results - the collection of result objects, may be updated
        Throws:
        IOException - if an I/O Error occurs
      • handleIsCancelled

        protected boolean handleIsCancelled(File file,
                                            int depth,
                                            Collection<T> results)
                                     throws IOException
        Deprecated. 
        Overridable callback method invoked to determine if the entire walk operation should be immediately cancelled.

        This method should be implemented by those subclasses that want to provide a public cancel() method available from another thread. The design pattern for the subclass should be as follows:

          public class FooDirectoryWalker extends DirectoryWalker {
            private volatile boolean cancelled = false;
        
            public void cancel() {
                cancelled = true;
            }
            private void handleIsCancelled(File file, int depth, Collection results) {
                return cancelled;
            }
            protected void handleCancelled(File startDirectory,
                      Collection results, CancelException cancel) {
                // implement processing required when a cancellation occurs
            }
          }
         

        If this method returns true, then the directory walk is immediately cancelled. The next callback method will be handleCancelled(java.io.File, java.util.Collection<T>, org.apache.commons.io.DirectoryWalker.CancelException).

        This implementation returns false.

        Parameters:
        file - the file or directory being processed
        depth - the current directory level (starting directory = 0)
        results - the collection of result objects, may be updated
        Returns:
        true if the walk has been cancelled
        Throws:
        IOException - if an I/O Error occurs
      • handleCancelled

        protected void handleCancelled(File startDirectory,
                                       Collection<T> results,
                                       DirectoryWalker.CancelException cancel)
                                throws IOException
        Deprecated. 
        Overridable callback method invoked when the operation is cancelled. The file being processed when the cancellation occurred can be obtained from the exception.

        This implementation just re-throws the DirectoryWalker.CancelException.

        Parameters:
        startDirectory - the directory that the walk started from
        results - the collection of result objects, may be updated
        cancel - the exception throw to cancel further processing containing details at the point of cancellation.
        Throws:
        IOException - if an I/O Error occurs
      • handleStart

        protected void handleStart(File startDirectory,
                                   Collection<T> results)
                            throws IOException
        Deprecated. 
        Overridable callback method invoked at the start of processing.

        This implementation does nothing.

        Parameters:
        startDirectory - the directory to start from
        results - the collection of result objects, may be updated
        Throws:
        IOException - if an I/O Error occurs
      • handleDirectory

        protected boolean handleDirectory(File directory,
                                          int depth,
                                          Collection<T> results)
                                   throws IOException
        Deprecated. 
        Overridable callback method invoked to determine if a directory should be processed.

        This method returns a boolean to indicate if the directory should be examined or not. If you return false, the entire directory and any subdirectories will be skipped. Note that this functionality is in addition to the filtering by file filter.

        This implementation does nothing and returns true.

        Parameters:
        directory - the current directory being processed
        depth - the current directory level (starting directory = 0)
        results - the collection of result objects, may be updated
        Returns:
        true to process this directory, false to skip this directory
        Throws:
        IOException - if an I/O Error occurs
      • handleDirectoryStart

        protected void handleDirectoryStart(File directory,
                                            int depth,
                                            Collection<T> results)
                                     throws IOException
        Deprecated. 
        Overridable callback method invoked at the start of processing each directory.

        This implementation does nothing.

        Parameters:
        directory - the current directory being processed
        depth - the current directory level (starting directory = 0)
        results - the collection of result objects, may be updated
        Throws:
        IOException - if an I/O Error occurs
      • filterDirectoryContents

        protected File[] filterDirectoryContents(File directory,
                                                 int depth,
                                                 File... files)
                                          throws IOException
        Deprecated. 
        Overridable callback method invoked with the contents of each directory.

        This implementation returns the files unchanged

        Parameters:
        directory - the current directory being processed
        depth - the current directory level (starting directory = 0)
        files - the files (possibly filtered) in the directory, may be null
        Returns:
        the filtered list of files
        Throws:
        IOException - if an I/O Error occurs
        Since:
        2.0
      • handleFile

        protected void handleFile(File file,
                                  int depth,
                                  Collection<T> results)
                           throws IOException
        Deprecated. 
        Overridable callback method invoked for each (non-directory) file.

        This implementation does nothing.

        Parameters:
        file - the current file being processed
        depth - the current directory level (starting directory = 0)
        results - the collection of result objects, may be updated
        Throws:
        IOException - if an I/O Error occurs
      • handleRestricted

        protected void handleRestricted(File directory,
                                        int depth,
                                        Collection<T> results)
                                 throws IOException
        Deprecated. 
        Overridable callback method invoked for each restricted directory.

        This implementation does nothing.

        Parameters:
        directory - the restricted directory
        depth - the current directory level (starting directory = 0)
        results - the collection of result objects, may be updated
        Throws:
        IOException - if an I/O Error occurs
      • handleDirectoryEnd

        protected void handleDirectoryEnd(File directory,
                                          int depth,
                                          Collection<T> results)
                                   throws IOException
        Deprecated. 
        Overridable callback method invoked at the end of processing each directory.

        This implementation does nothing.

        Parameters:
        directory - the directory being processed
        depth - the current directory level (starting directory = 0)
        results - the collection of result objects, may be updated
        Throws:
        IOException - if an I/O Error occurs
      • handleEnd

        protected void handleEnd(Collection<T> results)
                          throws IOException
        Deprecated. 
        Overridable callback method invoked at the end of processing.

        This implementation does nothing.

        Parameters:
        results - the collection of result objects, may be updated
        Throws:
        IOException - if an I/O Error occurs

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