How do I read a file into byte array using Apache Commons IO?

The following example shows you how to read file contents into byte array. We use the IOUtils class of the Apache Commons IO library.

package org.kodejava.commons.io;

import org.apache.commons.io.IOUtils;

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

public class FileToByteArray {
    public static void main(String[] args) {
        File file = new File("README.md");
        try {
            InputStream is = new FileInputStream(file);
            byte[] bytes = IOUtils.toByteArray(is);

            System.out.println("Byte array size: " + bytes.length);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.16.1</version>
</dependency>

Maven Central

How do I get the content of an InputStream as a String?

We can use the code below to convert the content of an InputStream into a String. At first, we use FileInputStream create to a stream to a file that going to be read. IOUtils.toString(InputStream input, String encoding) method gets the content of the InputStream and returns a string representation of it.

package org.kodejava.commons.io;

import org.apache.commons.io.IOUtils;

import java.io.InputStream;
import java.io.FileInputStream;
import java.nio.charset.StandardCharsets;

public class InputStreamToString {
    public static void main(String[] args) throws Exception {
        // Create an input stream for reading data.txt file content.
        try (InputStream is = new FileInputStream("data.txt")) {
            // Get the content of an input stream as a string using UTF-8
            // as the character encoding.
            String contents = IOUtils.toString(is, StandardCharsets.UTF_8);
            System.out.println(contents);
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.16.1</version>
</dependency>

Maven Central