How to read file using Files.newBufferedReader?

In the snippet below you’ll learn to open file for reading using Files.newBufferedReader() method in JDK 7. This method returns a java.io.BufferedReader which makes a backward compatibility with the old I/O system in Java.

To read a file you’ll need to provide a Path and the Charset to the newBufferedReader() method arguments.

package org.kodejava.example.io;

import java.io.BufferedReader;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class FilesNewBufferedReader {
    public static void main(String[] args) {
        Path logFile = Paths.get("D:/Temp/logs/app.log");
        try (BufferedReader reader = 
                 Files.newBufferedReader(logFile, StandardCharsets.UTF_8)) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

How to write file using Files.newBufferedWriter?

To open a file for writing in JDK 7 you can use the Files.newBufferedWriter() method. This method takes three arguments. We need to pass the Path, the Charset and a varargs of OpenOption.

For example, in the snippet below we pass the path of our log file, we use the StandardCharsets.UTF_8 charset and we use the StandardOpenOption.WRITE to open a file for writing. If you want to open a file and append its contents instead of rewriting it you can use the StandardOpenOption.APPEND.

package org.kodejava.example.io;

import java.io.BufferedWriter;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class FilesNewBufferedWriter {
    public static void main(String[] args) {
        Path logFile = Paths.get("app.log");
        try (BufferedWriter writer = 
                 Files.newBufferedWriter(logFile, StandardCharsets.UTF_8, 
                     StandardOpenOption.WRITE)) {

            for (int i = 0; i < 10; i++) {
                writer.write(String.format("Message %s%n", i));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Because we use the StandardOpenOption.WRITE we have to make sure that the file to be written is exists. If the file is not available we will get error like java.nio.file.NoSuchFileException.

How do I move a file in JDK 7?

In the following code snippet you will learn how to move a file using the java.nio.file.Files helper class of JDK 7. This class simplify how you can move file. To move file you need to define the Path of the source and the target file.

We use the Files.move() method to move the file by passing the source and target path. We can also define the CopyOptions of the move process. For example to tell the move operation to replace the target file if the file already exist we can use the StandardCopyOption.REPLACE_EXISTING option. This option is a varargs, that means we can pass multiple options.

package org.kodejava.example.io;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

import static java.nio.file.StandardCopyOption.*;

public class FileMoveDemo {
    public static void main(String[] args) {
        // Define the source and target of the file to be moved.
        Path source = Paths.get("D:/Source/data.txt");
        Path target = Paths.get("D:/Backup/data.txt");

        try {
            // Move file from source to target using the defined
            // configuration (REPLACE_EXISTING)
            Files.move(source, target, REPLACE_EXISTING);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I find files in a directory using DirectoryStream?

In this example we are going to learn to use the DirectoryStream, which part of java.nio.file package, to find files in a directory. We are begin by creating a Path, the directory where the search will be conducted.

After that we create a DirectoryStream using Files.newDirectoryStream(). To create a directory stream we passed two arguments, the starting path and a glob expression. Below we use *.txt glob expression to filter all text files in the D:/Workbench.

To get all the entries of the directory stream we can use a foreach loop as can be seen below. We iterate each entries, which is a Path object. And we print the entries file name using the getFileName() method.

package org.kodejava.example.io;

import java.io.IOException;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class FindFilesInDirectory {
    public static void main(String[] args) {
        Path dir = Paths.get("D:/Workbench");

        try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, "*.txt")) {
            for (Path entry : stream) {
                System.out.println(entry.getFileName());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

You can also notice that in this example we are using the try-with-resource statement. This mean that the DirectoryStream will be closed appropriately when the process is done. This type of try statement is an improvement introduced in JDK 7.

How do I create and delete a file in JDK 7?

In this example you’ll learn how to create and delete a file. Using the new Files class helper from the JDK 7 you can create a file using the Files.createFile(Path) method. To delete a file you can use the Files.delete(Path) method.

Before create a file and delete a file we can check to see if the file is exist or not using the Files.exists(Path) method. In the code snippet below we’ll create a file when the file is not exist. And we’ll delete the file if the file is exist.

package org.kodejava.example.io;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class CreateDeleteFile {
    public static void main(String[] args) {
        try {
            // Create a config.cfg file under D:Temp directory.
            Path path = Paths.get("D:/Temp/config.cfg");
            if (!Files.exists(path)) {
                Files.createFile(path);
            }

            // Delete the path.cfg file specified by the Path.
            if (Files.exists(path)) {
                Files.delete(path);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

How to recursively list all text files in a directory?

In this example you’ll learn how to use the Files.walkFileTree() to walk through file tree. This method requires two parameters. The first parameter is the starting file, in this example we’ll start from drive D:. And the second parameter is the file visitor to invoke for each file. Here we’ll create a file visitor call FindTextFilesVisitor which extend the java.nio.file.SimpleFileVisitor.

To get all the text files (files end with .txt) we override the visitFile() defined by the SimpleFileVisitor. In this method we check if the file ends with .txt extension and print the file name when the extension match. And we continue to walk the file tree by returning FileVisitResult.CONTINUE.

package org.kodejava.example.io;

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

public class WalkFileTree {
    public static void main(String[] args) {
        try {
            Path startDir = Paths.get("D:/");
            Files.walkFileTree(startDir, new FindTextFilesVisitor());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * FindTextFilesVisitor.
     */
    static class FindTextFilesVisitor extends SimpleFileVisitor<Path> {
        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
            if (file.toString().endsWith(".txt")) {
                System.out.println(file.getFileName());
            }
            return FileVisitResult.CONTINUE;
        }
    }
}

Instead of listing files, you can modify the code snippet above for instance use it to delete all the files that ends with .bak. Simply change the extension and replace the print out statement with a file delete statement in the visitFile() method.

How do I create a java.nio.Path?

The following code snippet show you how to create a Path. A Path (java.nio.Path) in an interface that represent a location in a file system, such as C:/Windows/System32 or /usr/bin.

To create a Path we can use the java.nio.Paths.get(String first, String... more) methods. Below you can see how to create a Path by passing only the first string and by passing a first string plus some varargs string.

package org.kodejava.example.io;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class PathCreate {
    public static void main(String[] args) {
        // Create a Path that represents Windows installation location.
        Path windows = Paths.get("C:/Windows");

        // Check to see if the path represent a directory.
        if (Files.isDirectory(windows)) {
            // do something
        }

        // Create a Path that represent Windows programs installation location.
        Path programFiles = Paths.get("C:/Program Files");
        Files.isDirectory(programFiles);

        // Create a Path that represent the notepad.exe program
        Path notepad = Paths.get("C:/Windows", "System32", "notepad.exe");

        // Check to see if the path represent an executable file.
        if (Files.isExecutable(notepad)) {
            // do something
        }
    }
}

How do I use the DosFileAttributes class?

This example show you how to use the DosFileAttributes class to get file attribute that support DOS file system. This class extends the BasicFileAttributes class. Using the DosFileAttributes class we can read file attributes using isArchive(), isHidden(), isReadOnly() and isSystem() methods.

Let’s see the code snippet below:

package org.kodejava.example.io;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.DosFileAttributes;

public class DosFileAttributeExample {
    public static void main(String[] args) throws Exception {
        String path = "D:/resources/data.txt";

        Path file = Paths.get(path);
        DosFileAttributes attr = Files.readAttributes(file, DosFileAttributes.class);

        System.out.println("isArchive()  = " + attr.isArchive());
        System.out.println("isHidden()   = " + attr.isHidden());
        System.out.println("isReadOnly() = " + attr.isReadOnly());
        System.out.println("isSystem()   = " + attr.isSystem());
    }
}

The output of the code snippet:

isArchive()  = true
isHidden()   = false
isReadOnly() = true
isSystem()   = false

How do I write a text file in JDK 7?

In JDK 7 we can write all lines from a List of String into a file using the Files.write() method. We need to provide the Path of the file we want to write to, the List of strings and the charsets. Each line is a char sequence and is written to the file in sequence with each line terminated by the platform’s line separator.

Let’s see the code snippet below:

package org.kodejava.example.io;

import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

public class WriteTextFile {
    public static void main(String[] args) {
        Path file = Paths.get("D:/resources/data.txt");

        List<String> lines = new ArrayList<>();
        lines.add("Lorem Ipsum is simply dummy text of the printing ");
        lines.add("and typesetting industry. Lorem Ipsum has been the ");
        lines.add("industry's standard dummy text ever since the 1500s, ");
        lines.add("when an unknown printer took a galley of type and ");
        lines.add("scrambled it to make a type specimen book.");

        try {
            // Write lines of text to a file.
            Files.write(file, lines, StandardCharsets.UTF_8);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

This code snippet will create a file called data.txt under the resources folder. Please make sure that this folder is exist before you tried to run the code.

How do I read all lines from a file?

The java.nio.file.Files.readAllLines() method read all lines from a file. This method ensures that the file is closed when all bytes have been read or an I/O error, or other runtime exception, is thrown. Bytes from the file are decoded into characters using the specified charset.

Note that this method is intended for simple cases where it is convenient to read all lines in a single operation. It is not intended for reading in large files. This method is available in Java 7.

package org.kodejava.example.io;

import java.net.URI;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;

public class ReadFileAsListDemo {
    public static void main(String[] args) {
        ReadFileAsListDemo demo = new ReadFileAsListDemo();
        demo.readFileAsList();
    }

    private void readFileAsList() {
        String fileName = "/data.txt";

        try {
            URI uri = this.getClass().getResource(fileName).toURI();
            List<String> lines = Files.readAllLines(Paths.get(uri),
                Charset.defaultCharset());

            for (String line : lines) {
                System.out.println(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}