Java - 遍历目录中的所有文件

Question

I want to find all the txt files in directory and in the nested sub-directories. If found, I want to move that from one location to another.

The below code works fine, if i don't have any nested sub-directories.

The problem with the below code is, Once it find the nested directories it return the file only from that particular nested sub-directory. But I want all the txt files in my directory ( parent and its nested sub-directories ).

public class FilesFindingInDirectory {
    static ArrayList<File> al = new ArrayList<File>();
    static File fileLocation = null;
    public static void main(String[] args) throws IOException {


        File filePath = new File("C:\\Users\\Downloads");

        File[] listingAllFiles = filePath.listFiles();

        ArrayList<File> allFiles = iterateOverFiles(listingAllFiles);


                for (File file : allFiles) {
                    if(file != null) {
                        String fileName = file.getName();

                        String sourceFilepath = file.getAbsolutePath();
                        File targetFilePath = new File("D:\\TestFiles");
                        String targetPath = targetFilePath.getPath();

                        Files.move(Paths.get(sourceFilepath), Paths.get("D:\\TestFiles\\" + fileName)); 
                    }

                }
            }


public static ArrayList<File> iterateOverFiles(File[] files) {


        for (File file : files) {

            if (file.isDirectory()) {

                iterateOverFiles(file.listFiles());// Calls same method again.

            } else {

                fileLocation = findFileswithTxtExtension(file);
                if(fileLocation != null) {
                    System.out.println(fileLocation);
                    al.add(fileLocation);
                }


            }
        }

        return al;
    }

public static File findFileswithTxtExtension(File file) {

        if(file.getName().toLowerCase().endsWith("txt")) {
            return file;
        }

        return null;
    }
}

Answer 1

You're already using the nio Files API to move the files, why not using it to iterate over the files?

 List<Path> txtFiles = Files.walk(Paths.get("C:\\Users\\Downloads"))
                            //use to string here, otherwise checking for path segments
                            .filter(p -> p.toString().endsWith(".txt"))
                            .collect(Collectors.toList());

If you don't need that intermediary list, you could as well run your move operation in a foreach terminal operation

Files.walk(Paths.get("C:\\Users\\Downloads"))
     .filter(p -> p.toString().endsWith(".txt"))
     .forEach(p -> {
        try {
            Files.move(p, Paths.get("D:\\TestFiles", p.getFileName().toString()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    });

Answer 2

From your recursive function remove this line:

return al;

change this line to just call the recursive function:

ArrayList<File> allFiles = iterateOverFiles(listingAllFiles);

to

iterateOverFiles(listingAllFiles);

and finally change your for loop to iterate over the static field al.

for (File file : allFiles) {

to

for (File file : al) {

Explanation: There are numerous ways to write recursion for this problem. In this case you have a global variable for collecting the results. Each iteration should add to that global result, and simply return. At the end of all recursion calls, the global variable will contain all the results.

Answer 3

You are properly calling the function recursively, but you're then ignoring its return value. Instead, you should append it to the result list:

public static List<File> iterateOverFiles(File[] files) {
    List<File> result = new ArrayList<>();
    for (File file : files) {
        if (file.isDirectory()) {
            result.addAll(iterateOverFiles(file.listFiles()); // Here!
        } else {
            fileLocation = findFileswithTxtExtension(file);
            if(fileLocation != null) {
                result.add(fileLocation);
            }
        }
    }

    return result;
}

Answer 4

Just iterate over a directory, skipping any non-directory entries and entries that do not have the desired extension. Add all files with the correct extension to a result, and do that recursively for each directory.

public class FilesFindingInDirectory {
   public static void main(String[] args) throws IOException {


    File filePath = new File("C:\\Users\\Downloads");


    Collection<File> allFiles = findFiles(filePath, ".txt");
    allFiles.forEach(file -> {
                    String fileName = file.getName();

                    String sourceFilepath = file.getAbsolutePath();
                    File targetFilePath = new File("D:\\TestFiles");
                    String targetPath = targetFilePath.getPath();

                    Files.move(Paths.get(sourceFilepath), Paths.get("D:\\TestFiles\\" + fileName)); 
                }

            }
        }

public static List<File> findFiles(File dir, String extension) {
    File[] files = dir.listFiles(f -> f.isDirectory() || f.getName().toLowerCase().endsWith(extension);
    ArrayList<File> result = new ArrayList<>();  
    if (files != null) {
       for (File file : files) {

        if (file.isDirectory()) {
            result.addAll(findFiles(file, extension);
        } else {
            result.add(file);
        }

    }

    return result;
  }
}