How to traverse all files from a folder in Java

In Java, we can use the Files.walk() API to traverse all files from a folder and its subfolders.

Table of contents:

• 1. Traverse all files from a folder in Java
• 2. Traverse all files from a folder and its subfolders in Java
• 3. List all file name from a folder in Java
• 4. Find a file from a folder and its subfolders in Java
• 5. Download Source Code
• 6. References

P.S Tested with Java 21

1. Traverse all files from a folder in Java

Let’s assume the folder /Users/mkyong/projects/test/ contains the following files:

|-- a.txt
|-- b.txt
|-- bootstrap-icons.min.css
|-- example.tar.gz

The following example uses Files.walk() API to traverse all files’ and directories’s paths from a folder, filter it to include only the files Files::isRegularFile and print out the file path.

package com.mkyong.io.howto;

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

public class FileTraverseExample {

    public static void main(String[] args) {

        // Specify the directory we want to traverse
        String dirPath = "/Users/yongmookkim/projects/test/";

        // Traverse the directory and process files
        try (Stream<Path> paths = Files.walk(Paths.get(dirPath))) {

            paths
                    .filter(Files::isRegularFile)  // ensure it is a file
                    .forEach(System.out::println); // prints the file path

        } catch (IOException e) {
            throw new RuntimeException(e);
        }

    }
}

Output

/Users/mkyong/projects/test/example.tar.gz
/Users/mkyong/projects/test/bootstrap-icons.min.css
/Users/mkyong/projects/test/b.txt
/Users/mkyong/projects/test/a.txt

2. Traverse all files from a folder and its subfolders in Java

It works the same; the Files.walk() API also traverses all files from a folder and its subfolders.

|-- a.txt
|-- b.txt
|-- bootstrap-icons.min.css
|-- example.tar.gz
|-- folderA
|   |-- c.txt
|   \-- folderB
|       \-- d.txt

    // Specify the directory we want to traverse
    String dirPath = "/Users/yongmookkim/projects/test/";

    // Traverse the directory and process files
    try (Stream<Path> paths = Files.walk(Paths.get(dirPath))) {

        paths
                .filter(Files::isRegularFile)  // ensure it is a file
                .forEach(System.out::println); // prints the file path

    } catch (IOException e) {
        throw new RuntimeException(e);
    }

Output

/Users/mkyong/projects/test/example.tar.gz
/Users/mkyong/projects/test/bootstrap-icons.min.css
/Users/mkyong/projects/test/b.txt
/Users/mkyong/projects/test/a.txt
/Users/mkyong/projects/test/folderA/folderB/d.txt
/Users/mkyong/projects/test/folderA/c.txt

3. List all file name from a folder in Java

The following example uses the Files.walk() API to traverse and collect all the file names from a folder and its subfolders. In the final step, the program will print out the total number of files collected and all the filenames.

package com.mkyong.io.howto;

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.Stream;

public class FileTraverseExample2 {

    public static void main(String[] args) {

        List<String> result;

        // Specify the directory we want to traverse
        String dirPath = "/Users/yongmookkim/projects/test/";

        // Traverse the directory and process files
        try (Stream<Path> paths = Files.walk(Paths.get(dirPath))) {

            result = paths
                    .filter(Files::isRegularFile)  // ensure it is a file
                    .map(p -> p.getFileName().toString())
                    .toList();

        } catch (IOException e) {
            throw new RuntimeException(e);
        }

        System.out.println("Total files: " + result.size());
        for (String name : result) {
            System.out.println("FileName: " + name);
        }


    }
}

Output

Total files: 5
FileName: example.tar.gz
FileName: bootstrap-icons.min.css
FileName: b.txt
FileName: a.txt
FileName: d.txt
FileName: c.txt

4. Find a file from a folder and its subfolders in Java

The following example uses the Files.walk() API to find a specific file name a.txt from a folder and its subfolders.

package com.mkyong.io.howto;

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

public class FileTraverseExample3 {

    public static void main(String[] args) {

        String dir = "/Users/yongmookkim/projects/test/";
        String findThisFile = "a.txt";

        try {

            Optional<Path> foundFile = findFileByName(Paths.get(dir), findThisFile);
            foundFile.ifPresentOrElse(
                    file -> System.out.println("File found: " + file),
                    () -> System.out.println("File not found.")
            );

        } catch (IOException e) {
            System.err.println("An error occurred while searching for the file: " + e.getMessage());
        }

    }

    public static Optional<Path> findFileByName(Path directory, String fileName) throws IOException {
        try (Stream<Path> stream = Files.walk(directory)) {
            return stream
                    .filter(Files::isRegularFile)
                    .filter(path -> path.getFileName().toString().equals(fileName))
                    .findFirst();
        }
    }

}

Output

/Users/mkyong/projects/test/a.txt

5. Download Source Code

6. References

• Oracle – Walking the File Tree
• Java Files.walk examples
• How to get size of a directory in Java
• How to read a file in Java
• Java – How to list all files in a directory

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