Java Files.walk examples

The Files.walk API is available since Java 8; it helps to walk a file tree at a given starting path.

1. Files.walk() method signature

Review the Files.walk method signature.

Files.java

    public static Stream<Path> walk(Path start, FileVisitOption... options)
        throws IOException {

        return walk(start, Integer.MAX_VALUE, options);
    }

    public static Stream<Path> walk(Path start,
                                    int maxDepth,
                                    FileVisitOption... options)
        throws IOException
    {

• The path, starting file or folder.
• The maxDepth, maximum number of directory levels to search, if omitted, default is Integer.MAX_VALUE, which means 2,147,483,647 directory levels to search. In short, by default, it will search all levels of the directory. If we want to search from the top-level or root directory only, puts 1.
• The FileVisitOption tells if we want to follow symbolic links, default is no. We can put FileVisitOption.FOLLOW_LINKS to follow symbolic links.

2. List all files

This example uses Files.walk to list all files from a directory, including all levels of sub-directories (default).

FilesWalkExample1.java

package com.favtuts.io.api;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class FilesWalkExample1 {

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

        Path path = Paths.get("C:\\test\\");
        List<Path> paths = listFiles(path);
        paths.forEach(x -> System.out.println(x));

    }

    // list all files from this path
    public static List<Path> listFiles(Path path) throws IOException {

        List<Path> result;
        try (Stream<Path> walk = Files.walk(path)) {
            result = walk.filter(Files::isRegularFile)
                    .collect(Collectors.toList());
        }
        return result;

    }

}

Output

C:\test\bk\logo-new.png
C:\test\bk\New Text Document.txt
C:\test\bk\readme.encrypted.txt
C:\test\bk\readme.txt
C:\test\data\ftp\google.png
C:\test\example.json
C:\test\google-decode.png
C:\test\google.png

If we want to list files from the root directory only, put maxDepth = 1.

FilesWalkExample1.java

    try (Stream<Path> walk = Files.walk(path, 1)) {
        result = walk.filter(Files::isRegularFile)
                .collect(Collectors.toList());
    }

Output

C:\test\example.json
C:\test\google-decode.png
C:\test\google.png

3. List all folders or directories

    // list all directories from this path
    public static List<Path> listDirectories(Path path) throws IOException {

        List<Path> result;
        try (Stream<Path> walk = Files.walk(path)) {
            result = walk.filter(Files::isDirectory)
                    .collect(Collectors.toList());
        }
        return result;

    }

Output

C:\test
C:\test\bk
C:\test\data
C:\test\data\ftp
C:\test\test1
C:\test\test1\test2

4. Find files by file extension

This example uses Files.walk to find all text files .txt from a path.

FilesWalkExample4.java

package com.favtuts.io.api;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class FilesWalkExample4 {

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

        Path path = Paths.get("C:\\test\\");
        List<Path> paths = findByFileExtension(path, ".txt");
        paths.forEach(x -> System.out.println(x));

    }

    public static List<Path> findByFileExtension(Path path, String fileExtension)
            throws IOException {

        if (!Files.isDirectory(path)) {
            throw new IllegalArgumentException("Path must be a directory!");
        }

        List<Path> result;
        try (Stream<Path> walk = Files.walk(path)) {
            result = walk
                    .filter(Files::isRegularFile)   // is a file
                    .filter(p -> p.getFileName().toString().endsWith(fileExtension))
                    .collect(Collectors.toList());
        }
        return result;

    }

}

Output

C:\test\bk\New Text Document.txt
C:\test\bk\readme.encrypted.txt
C:\test\bk\readme.txt

5. Find files by filename

  public static List<Path> findByFileName(Path path, String fileName)
      throws IOException {

      if (!Files.isDirectory(path)) {
          throw new IllegalArgumentException("Path must be a directory!");
      }

      List<Path> result;
      // walk file tree, no more recursive loop
      try (Stream<Path> walk = Files.walk(path)) {
          result = walk
                  .filter(Files::isReadable)      // read permission
                  .filter(Files::isRegularFile)   // is a file
                  .filter(p -> p.getFileName().toString().equalsIgnoreCase(fileName))
                  .collect(Collectors.toList());
      }
      return result;

  }

6. Find files by file size

Find all files containing file size greater or equal to 10MB.

FilesWalkExample6.java

package com.favtuts.io.api;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

// Files.walk example
public class FilesWalkExample6 {

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

        Path path = Paths.get("C:\\test\\");

        long fileSizeInBytes = 1024 * 1024 * 10; // 10MB

        List<Path> paths = findByFileSize(path, fileSizeInBytes);
        paths.forEach(x -> System.out.println(x));

    }

    // fileSize in bytes
    public static List<Path> findByFileSize(Path path, long fileSize)
        throws IOException {

        if (!Files.isDirectory(path)) {
            throw new IllegalArgumentException("Path must be a directory!");
        }

        List<Path> result;
        // walk file tree, no more recursive loop
        try (Stream<Path> walk = Files.walk(path)) {
            result = walk
                    .filter(Files::isReadable)              // read permission
                    .filter(p -> !Files.isDirectory(p))     // is a file
                    .filter(p -> checkFileSize(p, fileSize))
                    .collect(Collectors.toList());
        }
        return result;

    }

    private static boolean checkFileSize(Path path, long fileSize) {
        boolean result = false;
        try {
            if (Files.size(path) >= fileSize) {
                result = true;
            }
        } catch (IOException e) {
            System.err.println("Unable to get the file size of this file: " + path);
        }
        return result;
    }

}

7. Update all files last modified date

This example update all files’ last modified date from a path to yesterday.

FilesWalkExample7.java

package com.favtuts.io.api;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.FileTime;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.stream.Stream;

public class FilesWalkExample7 {

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

        Path path = Paths.get("C:\\test\\");

        Instant yesterday = Instant.now().minus(1, ChronoUnit.DAYS);
        setAllFilesModifiedDate(path, yesterday);

    }

    // set all files' last modified time to this instant
    public static void setAllFilesModifiedDate(Path path, Instant instant)
        throws IOException {

        try (Stream<Path> walk = Files.walk(path)) {
            walk
                    .filter(Files::isReadable)      // read permission
                    .filter(Files::isRegularFile)   // file only
                    .forEach(p -> {
                        try {
                            // set last modified time
                            Files.setLastModifiedTime(p, FileTime.from(instant));
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    });
        }
    }

}

Download Source Code

$ git clone https://github.com/favtuts/java-core-tutorials-examples

$ cd java-io

References

• Files.walk JavaDoc
• Java Files.find examples
• Java – Update last modified date of a file