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Using Files walkFileTree Method

There are several common uses of Files walkFileTree  method.
1.       Finding File

import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.*;

class FileFindVisitor extends SimpleFileVisitor<Path> {
    private PathMatcher matcher;
    public FileFindVisitor(String pattern){
        try {
matcher = FileSystems.getDefault().getPathMatcher(pattern);
        } catch(IllegalArgumentException e) {
            e.printStackTrace();
        }
    }
    public FileVisitResult visitFile(Path path, BasicFileAttributes
fileAttributes){
        find(path);
        return FileVisitResult.CONTINUE;
    }
   
    private void find(Path path) {
        Path name = path.getFileName();
        if(matcher.matches(name))
            System.out.println("Match found:" + path.getFileName());
    }
   
    public FileVisitResult preVisitDirectory(Path path,
BasicFileAttributes fileAttributes){
        find(path);
        return FileVisitResult.CONTINUE;
    }
   
    public static void main(String[] args) {
        if(args.length != 2){
            System.out.println("usage: java FileTreeWalkFind <path>
<search pattern>");
            System.exit(−1);
        }

        Path path = Paths.get(args[0]);
        String pattern = args[1];
        try {
            Files.walkFileTree(path, new FileFindVisitor(pattern));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}






2.       Deleting Directories

Before deleting a directory all files contained in that directory must be deleted.

import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.*;

class DeleteDirVisitor extends 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;
         }
     }
   
    public static void main(String[] args) {
        if(args.length != 1){
            System.out.println("usage: java DeleteDirVisitor <dir-to-
remove>");
            System.exit(−1);
        }
        Path path = Paths.get(args[0]);
        try {
            Files.walkFileTree(path, new DeleteDirVisitor());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

3.       Copying Directories
Copying a directory tree requires following symbolink links and seperate copying of all subdirectories and files.


import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.*;

class CopyDirVisitor extends SimpleFileVisitor<Path> {
    Path source = null;
    Path target = null;
   
    public CopyDirVisitor(Path source,Path target){
        this.source = source;
        this.target = target;
    }
   
    @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;
     }
   
    public static void main(String[] args) {
        if(args.length != 2){
            System.out.println("usage: java CopyDirVisitor <source-
dir-to-copy-from> <target-dir-to-copy-to> ");
            System.exit(−1);
        }
        Path source = Paths.get(args[0]);
        Path destination = Paths.get(args[1]);
        try {
            Files.walkFileTree(source,EnumSet.of(FileVisitOption.FOLLOW_LINKS), Integer.MAX_VALUE, new CopyDirVisitor(source,destination));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}


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