Java: Convert InputStream to ByteArray

Approach 1: Read entire input stream to ByteArrayOutputStream.

public static byte[] getByteArray(InputStream inputStream) throws IOException {

         ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

         int nRead;

         byte[] data = new byte[16384];

         try {

                  while ((nRead = inputStream.read(data, 0, data.length)) != -1) {

                           byteArrayOutputStream.write(data, 0, nRead);

                  }

         } catch (IOException e) {

                  e.printStackTrace();

                  if (inputStream != null) {

                           inputStream.close();

                  }

         }

         return byteArrayOutputStream.toByteArray();

}

App.java

package com.sample.app;

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

public class App {

 public static byte[] getByteArray(InputStream inputStream) throws IOException {
  ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

  int nRead;
  byte[] data = new byte[16384];

  try {
   while ((nRead = inputStream.read(data, 0, data.length)) != -1) {
    byteArrayOutputStream.write(data, 0, nRead);
   }
  } catch (IOException e) {
   e.printStackTrace();
   if (inputStream != null) {
    inputStream.close();
   }
  }

  return byteArrayOutputStream.toByteArray();
 }

 public static void main(String args[]) throws IOException {
  FileInputStream fis = new FileInputStream(new File("/Users/krishna/Desktop/TODO.txt"));
  byte[] data = getByteArray(fis);
  
  System.out.println(new String(data));
 }
}

Approach 2: From Java9 onwards, inputstream class provides ‘readAllBytes’ method to get byte array from input stream.

public byte[] readAllBytes​()

public int readNBytes​(byte[] b, int off, int len)

Approach 3: Using DataInputStream.

byte[] bytes = new byte[(int) file.length()];

try (DataInputStream dataInputStream = new DataInputStream(new FileInputStream(file));) {

         dataInputStream.readFully(bytes);

         return bytes;

}

App.java

package com.sample.app;

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

public class App {

 public static byte[] getByteArray(File file) throws IOException {

  byte[] bytes = new byte[(int) file.length()];
  
  try (DataInputStream dataInputStream = new DataInputStream(new FileInputStream(file));) {
   dataInputStream.readFully(bytes);
   return bytes;
  }

 }

 public static void main(String args[]) throws IOException {
  byte[] data = getByteArray(new File("/Users/krishna/Desktop/TODO.txt"));

  System.out.println(new String(data));
 }
}

You may like

Miscellaneous

Interview Questions

Programming Questions

Pad integer with zeros

How to create ArrayList from Array

Get path to System desktop

How to get the current directory path?

Open a file