java.nio.file

Interface FileVisitor<T>

  • All Known Implementing Classes:
    SimpleFileVisitor 

    public interface FileVisitor<T>
    A visitor of files. An implementation of this interface is provided to the Files.walkFileTree methods to visit each file in a file tree.

    Usage Examples: Suppose we want to delete a file tree. In that case, each directory should be deleted after the entries in the directory are deleted. 

         Path start = ...
     Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
         @Override
         public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
             throws IOException
         {
             Files.delete(file);
             return FileVisitResult.CONTINUE;
         }
         @Override
         public FileVisitResult postVisitDirectory(Path dir, IOException e)
             throws IOException
         {
             if (e == null) {
                 Files.delete(dir);
                 return FileVisitResult.CONTINUE;
             } else {
                 // directory iteration failed
                 throw e;
             }
         }
     });

    Furthermore, suppose we want to copy a file tree to a target location. In that case, symbolic links should be followed and the target directory should be created before the entries in the directory are copied. 

         final Path source = ...
     final Path target = ...

     Files.walkFileTree(source, EnumSet.of(FileVisitOption.FOLLOW_LINKS), Integer.MAX_VALUE,
         new SimpleFileVisitor<Path>() {
             @Override
             public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
                 throws IOException
             {
                 Path targetdir = target.resolve(source.relativize(dir));
                 try {
                     Files.copy(dir, targetdir);
                 } catch (FileAlreadyExistsException e) {
                      if (!Files.isDirectory(targetdir))
                          throw e;
                 }
                 return CONTINUE;
             }
             @Override
             public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
                 throws IOException
             {
                 Files.copy(file, target.resolve(source.relativize(file)));
                 return CONTINUE;
             }
         });
    Since:
    1.7

    • Method Detail

      • preVisitDirectory

        FileVisitResult preVisitDirectory(T dir,
                                  BasicFileAttributes attrs)
                           throws IOException
        Invoked for a directory before entries in the directory are visited.

        If this method returns CONTINUE, then entries in the directory are visited. If this method returns SKIP_SUBTREE or SKIP_SIBLINGS then entries in the directory (and any descendants) will not be visited.

        Parameters:
        dir - a reference to the directory
        attrs - the directory's basic attributes
        Returns:
        the visit result
        Throws:
        IOException - if an I/O error occurs

      • visitFileFailed

        FileVisitResult visitFileFailed(T file,
                                IOException exc)
                         throws IOException
        Invoked for a file that could not be visited. This method is invoked if the file's attributes could not be read, the file is a directory that could not be opened, and other reasons.
        Parameters:
        file - a reference to the file
        exc - the I/O exception that prevented the file from being visited
        Returns:
        the visit result
        Throws:
        IOException - if an I/O error occurs

      • postVisitDirectory

        FileVisitResult postVisitDirectory(T dir,
                                   IOException exc)
                            throws IOException
        Invoked for a directory after entries in the directory, and all of their descendants, have been visited. This method is also invoked when iteration of the directory completes prematurely (by a visitFile method returning SKIP_SIBLINGS, or an I/O error when iterating over the directory).
        Parameters:
        dir - a reference to the directory
        exc - null if the iteration of the directory completes without an error; otherwise the I/O exception that caused the iteration of the directory to complete prematurely
        Returns:
        the visit result
        Throws:
        IOException - if an I/O error occurs