IT. Expert System.

Java Standard Edition (SE)

FileVisitor


compact1, compact2, compact3
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


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