How to Copy a File in Java [Practical Examples]

Different methods to copy a file in Java

File handling is very important part of any application. Java provides several classes and methods to ease this task. The reading and writing operations are done easily with the help of this classes and methods.

The list below shows five different ways in which we can copy a file in Java.

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  • Using FileInputStream and FileOutputStream
  • Using Paths and Files
  • Using RandomAccessFile Class
  • Using FileChannel
  • Using Files.copy()

 

Using FileInputStream and FileOutputStream

This is a traditional approach to copy a file in Java. Firstly, we will create source file and destination file. Thereafter, we create InputStream from the source to read a file and write it to the destination file using OutputStream.

Example : In this example, content of test.txt will be copied to output.txt. Thereafter, we are reading the content of output file to verify the copy operation.

// Program to copy a file in Java
import java.io.*;

public class MyClass {

    public static void main(String[] args) {
        // Creating object of fileinputstream and fileoutputstream
        FileInputStream fin = new FileInputStream("test.txt");
        FileOutputStream fo = new FileOutputStream("output.txt");

        int c;
        // Reading file as a byte and writing to a output file
        while ((c = fin.read()) != -1) {
            fo.write(c);
        }

        System.out.println("File test.txt is copied successfully");
        fin.close();
        fo.close();

        //Reading a file to verify if content was copied
        System.out.println("-----Reading output file-----");
        File file = new File("output.txt");
        BufferedReader br = new BufferedReader(new FileReader(file));

        String st;
        while ((st = br.readLine()) != null)
            System.out.println(st);
    }

}

Output

File test.txt is copied successfully
-----Reading output file-----
Hello world
Welcome to the world of Java Programming

 

Using Paths and Files Class

In this approach we are using Paths class and Files class of java.nio.file package to copy a file. The Paths class consist of static methods that return a path by converting a path string to uri. Whereas, newInputStream method of Files class opens a file returning an input stream to read from the file. The newOutputStream method of Files class opens or creates a file returning an output stream that may be used to write bytes to the file.

Example : In this example, content of test.txt will be copied to output.txt. Thereafter, we are reading the content of output file to verify the copy operation.

// Program to copy a file in Java
import java.nio.file.Files;
import java.nio.file.Paths;
import java.io.*;

public class Main {

    public static void main(String[] args) throws IOException {
        var src = Paths.get("javademo/test.txt");
        var dest = Paths.get("javademo/output.txt");

        var fin = Files.newInputStream(src);
        var fo = Files.newOutputStream(dest);

        int c;
        // Reading file as a byte and writing to a output file
        while ((c = fin.read()) != -1) {
            fo.write(c);
        }

        System.out.println("File test.txt is copied successfully");
        fin.close();
        fo.close();

        //Reading a file to verify if content was copied
        System.out.println("-----Reading output file-----");
        File file = new File("output.txt");
        BufferedReader br = new BufferedReader(new FileReader(file));

        String st;
        while ((st = br.readLine()) != null)
            System.out.println(st);
    }

}

Output

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File test.txt is copied successfully
-----Reading output file-----
Hello world
Welcome to the world of Java Programming

 

Using RandomAccessFile Class

In this approach, we are using RandomAccessFile class of java.io package to copy a file. Here, it creates a random access file stream to read from, and optionally to write to, a file with the specified name. Thereafter, we are using read and write method to read from and write to a file respectively.

Example :In this example, content of test.txt will be copied to output.txt. Thereafter, we are reading the content of output file to verify the copy operation.

// Program to copy a file in Java
import java.io.RandomAccessFile;
import java.io.*;

public class MyClass {

    public static void main(String[] args) throws IOException {
        RandomAccessFile src = new RandomAccessFile("test.txt", "r");
        RandomAccessFile dest = new RandomAccessFile("output.txt", "rw");

        int c;
        // Reading file as a byte and writing to a output file
        while ((c = src.read()) != -1) {
            dest.write(c);
        }

        System.out.println("File test.txt is copied successfully");

        //Reading a file to verify if content was copied

        System.out.println("-----Reading output file-----");
        File file = new File("output.txt");
        BufferedReader br = new BufferedReader(new FileReader(file));

        String st;
        while ((st = br.readLine()) != null)
            System.out.println(st);
    }

}

Output

File test.txt is copied successfully
-----Reading output file-----
Java: write once, run away! –Brucee
If Java had true garbage collection, most programs would delete themselves upon execution. – Robert Sewell
Measuring programming progress by lines of code is like measuring aircraft building progress by weight. – Bill Gates

 

Using FileChannel Class

In this approach, we are using FileChannel Class of java.nio.channels package to copy a file. Here, we are creating a channel that cna be used for reading, writing, mapping and manipulating a file. Here, transferFrom method transfers bytes into this channel's file from the given readable byte channel. Alternatively, we can also use transferTo method to copy a file.

Example : In this example, content of test.txt will be copied to output.txt. Thereafter, we are reading the content of output file to verify the copy operation.

// Program to copy a file in Java
import java.nio.channels.FileChannel;
import java.io.*;

public class MyClass {

    public static void main(String[] args) throws IOException {
        FileChannel sf = new FileInputStream("test.txt").getChannel();
        FileChannel df = new FileOutputStream("output.txt").getChannel();

        df.transferFrom(sf, 0, sf.size());

        System.out.println("File test.txt is copied successfully");
        //Reading a file to verify if content was copied
        System.out.println("-----Reading output file-----");
        File file = new File("output.txt");
        BufferedReader br = new BufferedReader(new FileReader(file));

        String st;
        while ((st = br.readLine()) != null)
            System.out.println(st);
    }

}

Output

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File test.txt is copied successfully
-----Reading output file-----
Java: write once, run away! –Brucee
If Java had true garbage collection, most programs would delete themselves upon execution. – Robert Sewell
Measuring programming progress by lines of code is like measuring aircraft building progress by weight. – Bill Gates

 

Using Files.copy()

In this approach, we are using copy method of Files class of java.nio.file package to copy a file. Note that if output file is existing it will throw a FileAlreadyExists exception.

Example : In this example, content of test.txt will be copied to output.txt. Thereafter, we are reading the content of output file to verify the copy operation.

// Program to copy a file in Java
import java.nio.file.Files;
import java.io.*;

public class MyClass {

    public static void main(String[] args) throws IOException {
        File sf = new File("test.txt");
        File df = new File("output.txt");

        Files.copy(sf.toPath(), df.toPath());

        System.out.println("File test.txt is copied successfully");
        //Reading a file to verify if content was copied
        System.out.println("-----Reading output file-----");
        File file = new File("output.txt");
        BufferedReader br = new BufferedReader(new FileReader(file));

        String st;
        while ((st = br.readLine()) != null)
            System.out.println(st);
    }

}

Output

File test.txt is copied successfully
-----Reading output file-----
Java: write once, run away! –Brucee
If Java had true garbage collection, most programs would delete themselves upon execution. – Robert Sewell
Measuring programming progress by lines of code is like measuring aircraft building progress by weight. – Bill Gates

 

Summary

The knowledge of copying a file in Java is very useful while working on real time applications. In this tutorial, we covered five different approaches to copy a file in Java. As per the requirement of an application, we can choose an appropriate approach for copying. We learned in detail about this approaches with an example. All in all, this tutorial, covers everything that you need to know in order to have a clear view on copying a file in Java.

 

References

FileInputStream Class
FileOutputStream Class
Paths Class
Files Class
RandomAccessFile Class
FileChannel Class

 

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