In programmers life,We need to convert the files to byte array to sent over network.
There are different ways to convert file to byte array.

Table of Content :


Read file to byte[] array with FileInputStream


package com.javacodestuffs.io.files.convert.tobytes;

import java.io.File;
import java.io.FileInputStream;

public class ReadFileAsByteArray1 {
	public static void main(String[] args) {

		File file = new File("src/main/resources/abc.txt"); // this file we kept in classpath

		FileInputStream fileInputStream = null;
		byte[] bytes = new byte[(int) file.length()];
		try {
			// convert file into byte array

			fileInputStream = new FileInputStream(file);
			fileInputStream.read(bytes);
			fileInputStream.close();

			for (int i = 0; i < bytes.length; i++) {
				System.out.print((char) bytes[i]);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

output:

Hello World!!!

Read file to byte[] array with NIO 


package com.javacodestuffs.io.files.convert.tobytes;

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

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

			Path path = Paths.get("src/main/resources/abc.txt");
			byte[] data = Files.readAllBytes(path);
			System.out.println(data);
		}
	}
}

Read file to byte array using common.io's FileUtils

Using Apache commons IO's FileUtils and IOUtils class, we can convert or read file to byte array

Maven dependency

we need to include maven dependency in our maven project. 


<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.7</version>
</dependency>




import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;

public class ReadFileAsByteUsingApacheCommons {

	public static void main(String[] args) throws IOException {
		{
			// Using FileUtils.readFileToByteArray()
			File file1 = new File("src/main/resources/abc1.txt");
			File file2 = new File("src/main/resources/abc2.txt");

			FileInputStream fileInputStream = new FileInputStream(file1);

			byte[] bytes1 = FileUtils.readFileToByteArray(file2);

			// Using IOUtils.toByteArray
			byte[] bytes2 = IOUtils.toByteArray(fileInputStream);
           
           		System.out.println("printing the byte array content1:");
			for (int i = 0; i < bytes1.length; i++) {

				System.out.print((char) bytes1[i]);
			}
            
			System.out.println();
			System.out.println("printing the byte array content2:");
			for (int i = 0; i < bytes2.length; i++) {

				System.out.print((char) bytes2[i]);
			}

		}
	}
}

Read file to byte[] array using Google Guava

Another way to read files as byte array is use google Guava library.

Maven dependency 



<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>29.0-jre</version>
</dependency>




import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import com.google.common.io.ByteStreams;
import com.google.common.io.Files;

public class ReadFileAsByteUsingGuava {

	public static void main(String[] args) throws IOException {
		{
			// Using FileUtils.readFileToByteArray()
			File file1 = new File("src/main/resources/abc1.txt");
			File file2 = new File("src/main/resources/abc2.txt");
			
			//Using Files.toByteArray()
			byte[] bytes1 = Files.toByteArray(file1);

			//Using ByteStreams.toByteArray	
			FileInputStream fileInputStream = new FileInputStream(file2);
			byte[] bytes2 = ByteStreams.toByteArray(fileInputStream);
            
            ......
            .....

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In this article, we have seen Read file to byte[] array in Java. All source code in the article can be found in the GitHub repository.