Reading and Writing Images in Java using File streams

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In this article, we will learn how to read and write image objects using Java.

Reading Image:

To read an image, first create a java.io.File object.

File file = new File("location of image");

Create a byte array. This array will store image data, byte by byte. The size of this byte array will be the length of input file. i.e, file.length();

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

Create a FileInputStream object which will take file as a parameter. This object will read the image byte by byte and store it in the bytes array.

FileInputStream fis = new FileInputStream(file);

Read the bytes from FileInputStream object into the bytes array.

fis.read(bytes);

Close the FileInputStream

fis.close();

Complete Java code:

import java.io.File; import java.io.FileInputStream; import java.io.IOException; public class Example{ public static void main(String[] args) throws IOException{ File file = new File("Image location"); FileInputStream in = new FileInputStream(file); long size = file.length(); byte[] temp = new byte[(int)size]; in.read(temp); in.close(); } }

Writing Image to File :

We have loaded our image in the form of bytes array. This byte array can be written to file using FileOutputStream.
Create the file object for the new file.

File file = new File("new File location");

Create a FileOutputStream object and pass this file to it.

FileOutputStream fos = new FileOutputStream(file);

We will use bufferedOutputStream to wrap fos object as it is more efficient.

BufferedOutputStream bos = new BufferedOutputStream(fos);

Finally create a DataOutputStream object and pass bos to it.

DataOutputStream dos = new DataOutputStream(bos);

write the bytes array to dos and close it.

dos.write(bytes); dos.close();

Complete java code to write bytes array as new image file:

import java.io.BufferedOutputStream; import java.io.DataOutputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; public class temp{ public static void main(String[] args) throws IOException{ File file = new File("img.jpg"); // img.jpg can be any image file FileInputStream in = new FileInputStream(file); long size = file.length(); byte[] temp = new byte[(int)size]; in.read(temp); in.close(); // The img.jpg image data will be written in a new image File named "output.jpg" DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(new File("output.jpg")))); dos.write(temp); dos.close(); } }